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') in jQuery? ⭐⭐⭐⭐ 4530 | **Answer:** 4531 | Read Full Answer on 👉 FullStack.Cafe 4532 | 4533 | #### Q22: What is the difference between event.PreventDefault and "return false"? ⭐⭐⭐⭐ 4534 | **Answer:** 4535 | Read Full Answer on 👉 FullStack.Cafe 4536 | 4537 | #### Q23: How do you attach a event to element which should be executed only once? ⭐⭐⭐⭐ 4538 | **Answer:** 4539 | Read Full Answer on 👉 FullStack.Cafe 4540 | 4541 | #### Q24: In what situation you would use multiple version of jQuery and how would you include them? ⭐⭐⭐⭐ 4542 | **Answer:** 4543 | Read Full Answer on 👉 FullStack.Cafe 4544 | 4545 | #### Q25: Is there any advantage of using $.ajax() for ajax call against $.get() or $.post()? ⭐⭐⭐⭐ 4546 | **Answer:** 4547 | Read Full Answer on 👉 FullStack.Cafe 4548 | 4549 | #### Q26: What are deferred and promise object in jQuery? ⭐⭐⭐⭐ 4550 | **Answer:** 4551 | Read Full Answer on 👉 FullStack.Cafe 4552 | 4553 | #### Q27: How can I get jQuery to perform a synchronous, rather than asynchronous, Ajax request? ⭐⭐⭐⭐ 4554 | **Answer:** 4555 | Read Full Answer on 👉 FullStack.Cafe 4556 | 4557 | #### Q28: What are the differences between JavaScript's window.onload and jQuery's $(document).ready() method? ⭐⭐⭐⭐ 4558 | **Answer:** 4559 | Read Full Answer on 👉 FullStack.Cafe 4560 | 4561 | #### Q29: Is there any significant difference between event.preventDefault() vs. return false to stop event propagation? ⭐⭐⭐⭐ 4562 | **Answer:** 4563 | Read Full Answer on 👉 FullStack.Cafe 4564 | 4565 | #### Q30: Is it possible to hold or delay document.ready execution for sometime? ⭐⭐⭐⭐⭐ 4566 | **Answer:** 4567 | Read Full Answer on 👉 FullStack.Cafe 4568 | 4569 | #### Q31: Is it possible to get value of multiple CSS properties in single statement? ⭐⭐⭐⭐⭐ 4570 | **Answer:** 4571 | Read Full Answer on 👉 FullStack.Cafe 4572 | 4573 | #### Q32: How can I implement my own $(document).ready functionality without using jQuery? ⭐⭐⭐⭐⭐ 4574 | **Answer:** 4575 | Read Full Answer on 👉 FullStack.Cafe 4576 | 4577 | ## [[⬆]](#toc) 33 Frequently Asked Node.js Interview Questions (2020 Update) 4578 | > Originally published on 👉 33 Frequently Asked Node.js Interview Questions (2020 Update) | FullStack.Cafe 4579 | 4580 | #### Q1: What is Node.js? ⭐ 4581 | **Answer:** 4582 | Node.js is a web application framework built on Google Chrome's JavaScript Engine (V8 Engine). 4583 | 4584 | Node.js comes with runtime environment on which a Javascript based script can be interpreted and executed (It is analogus to JVM to JAVA byte code). This runtime allows to execute a JavaScript code on any machine outside a browser. Because of this runtime of Node.js, JavaScript is now can be executed on server as well. 4585 | 4586 | *Node.js = Runtime Environment + JavaScript Library* 4587 | 4588 | **Source:** _tutorialspoint.com_ 4589 | 4590 | #### Q2: What do you mean by Asynchronous API? ⭐⭐ 4591 | **Answer:** 4592 | All APIs of Node.js library are aynchronous that is non-blocking. It essentially means a Node.js based server never waits for a API to return data. Server moves to next API after calling it and a notification mechanism of Events of Node.js helps server to get response from the previous API call. 4593 | 4594 | **Source:** _tutorialspoint.com_ 4595 | 4596 | #### Q3: What are the benefits of using Node.js? ⭐⭐ 4597 | **Answer:** 4598 | Following are main benefits of using Node.js 4599 | 4600 | * **Aynchronous and Event Driven** - All APIs of Node.js library are aynchronous that is non-blocking. It essentially means a Node.js based server never waits for a API to return data. Server moves to next API after calling it and a notification mechanism of Events of Node.js helps server to get response from the previous API call. 4601 | * **Very Fast** - Being built on Google Chrome's V8 JavaScript Engine, Node.js library is very fast in code execution. 4602 | * **Single Threaded but highly Scalable** - Node.js uses a single threaded model with event looping. Event mechanism helps server to respond in a non-bloking ways and makes server highly scalable as opposed to traditional servers which create limited threads to handle requests. Node.js uses a single threaded program and same program can services much larger number of requests than traditional server like Apache HTTP Server. 4603 | * **No Buffering** \- Node.js applications never buffer any data. These applications simply output the data in chunks. 4604 | 4605 | **Source:** _tutorialspoint.com_ 4606 | 4607 | #### Q4: What are the key features of Node.js? ⭐⭐ 4608 | **Answer:** 4609 | Let’s look at some of the key features of Node.js. 4610 | 4611 | * **Asynchronous event driven IO helps concurrent request handling –** All APIs of Node.js are asynchronous. This feature means that if a Node receives a request for some Input/Output operation, it will execute that operation in the background and continue with the processing of other requests. Thus it will not wait for the response from the previous requests. 4612 | * **Fast in Code execution –** Node.js uses the V8 JavaScript Runtime engine, the one which is used by Google Chrome. Node has a wrapper over the JavaScript engine which makes the runtime engine much faster and hence processing of requests within Node.js also become faster. 4613 | * **Single Threaded but Highly Scalable –** Node.js uses a single thread model for event looping. The response from these events may or may not reach the server immediately. However, this does not block other operations. Thus making Node.js highly scalable. Traditional servers create limited threads to handle requests while Node.js creates a single thread that provides service to much larger numbers of such requests. 4614 | * **Node.js library uses JavaScript –** This is another important aspect of Node.js from the developer’s point of view. The majority of developers are already well-versed in JavaScript. Hence, development in Node.js becomes easier for a developer who knows JavaScript. 4615 | * **There is an Active and vibrant community for the Node.js framework –** The active community always keeps the framework updated with the latest trends in the web development. 4616 | * **No Buffering –** Node.js applications never buffer any data. They simply output the data in chunks. 4617 | 4618 | **Source:** _techbeamers.com_ 4619 | 4620 | #### Q5: What is libuv? ⭐⭐ 4621 | **Answer:** 4622 | **libuv** is a C library that is used to abstract non-blocking I/O operations to a consistent interface across all supported platforms. It provides mechanisms to handle file system, DNS, network, child processes, pipes, signal handling, polling and streaming. It also includes a thread pool for offloading work for some things that can't be done asynchronously at the operating system level. 4623 | 4624 | **Source:** _nodejs.org_ 4625 | 4626 | #### Q6: What is a blocking code? ⭐⭐⭐ 4627 | **Answer:** 4628 | If application has to wait for some I/O operation in order to complete its execution any further then the code responsible for waiting is known as blocking code. 4629 | 4630 | **Source:** _tutorialspoint.com_ 4631 | 4632 | #### Q7: What is difference between synchronous and asynchronous method of fs module? ⭐⭐⭐ 4633 | **Answer:** 4634 | 4635 | Every method in `fs` module has synchronous as well as asynchronous form. Asynchronous methods takes a last parameter as completion function callback and first parameter of the callback function is error. It is preferred to use asynchronous method instead of synchronous method as former never block the program execution where the latter one does. 4636 | 4637 | **Source:** _tutorialspoint.com_ 4638 | 4639 | #### Q8: What is Chaining in Node? ⭐⭐⭐ 4640 | **Answer:** 4641 | **Chanining** is a mechanism to connect output of one stream to another stream and create a chain of multiple stream operations. It is normally used with piping operations. 4642 | 4643 | **Source:** _tutorialspoint.com_ 4644 | 4645 | #### Q9: What's the event loop? ⭐⭐⭐ 4646 | **Answer:** 4647 | **The event loop** is what allows Node.js to perform non-blocking I/O operations — despite the fact that JavaScript is single-threaded — by offloading operations to the system kernel whenever possible. 4648 | 4649 |

4650 |

4651 |

4652 | 4653 | Every I/O requires a callback - once they are done they are pushed onto the event loop for execution. Since most modern kernels are multi-threaded, they can handle multiple operations executing in the background. When one of these operations completes, the kernel tells Node.js so that the appropriate callback may be added to the poll queue to eventually be executed. 4654 | 4655 | **Source:** _blog.risingstack.com_ 4656 | 4657 | #### Q10: When should we use Node.js? ⭐⭐⭐ 4658 | **Answer:** 4659 | **Node.js** is well suited for applications that have a lot of concurrent connections and each _request only needs very few CPU cycles_, because the event loop (with all the other clients) is blocked during execution of a function. I believe Node.js is best suited for real-time applications: online games, collaboration tools, chat rooms, or anything where what one user (or robot? or sensor?) does with the application needs to be seen by other users immediately, without a page refresh. 4660 | 4661 | **Source:** _techbeamers.com_ 4662 | 4663 | #### Q11: How does Node.js handle child threads? ⭐⭐⭐ 4664 | **Answer:** 4665 | Node.js, in its essence, is a single thread process. It does not expose child threads and thread management methods to the developer. Technically, Node.js does spawn child threads for certain tasks such as asynchronous I/O, but these run behind the scenes and do not execute any application JavaScript code, nor block the main event loop. 4666 | 4667 | If threading support is desired in a Node.js application, there are tools available to enable it, such as the ChildProcess module. 4668 | 4669 | **Source:** _lazyquestion.com_ 4670 | 4671 | #### Q12: What is the preferred method of resolving unhandled exceptions in Node.js? ⭐⭐⭐ 4672 | **Answer:** 4673 | Unhandled exceptions in Node.js can be caught at the `Process` level by attaching a handler for `uncaughtException` event. 4674 | 4675 | ```js 4676 | process.on('uncaughtException', function(err) { 4677 | console.log('Caught exception: ' + err); 4678 | }); 4679 | ``` 4680 | However, `uncaughtException` is a very crude mechanism for exception handling and may be removed from Node.js in the future. An exception that has bubbled all the way up to the `Process` level means that your application, and Node.js may be in an undefined state, and the only sensible approach would be to restart everything. 4681 | 4682 | The preferred way is to add another layer between your application and the Node.js process which is called the [domain](http://nodejs.org/api/domain.html). 4683 | 4684 | Domains provide a way to handle multiple different I/O operations as a single group. So, by having your application, or part of it, running in a separate domain, you can safely handle exceptions at the domain level, before they reach the `Process` level. 4685 | 4686 | **Source:** _lazyquestion.com_ 4687 | 4688 | #### Q13: How to use Buffer in Node.js? ⭐⭐⭐ 4689 | **Answer:** 4690 | Buffer is used to process binary data, such as pictures, mp3, database files, etc. Buffer supports a variety of encoding and decoding, binary string conversion. 4691 | 4692 | **Source:** _github.com/jimuyouyou_ 4693 | 4694 | #### Q14: Rewrite promise-based Node.js applications to Async/Await ⭐⭐⭐ 4695 | **Details:** 4696 | Rewrite this code to Async/Await: 4697 | ```js 4698 | function asyncTask() { 4699 | return functionA() 4700 | .then((valueA) => functionB(valueA)) 4701 | .then((valueB) => functionC(valueB)) 4702 | .then((valueC) => functionD(valueC)) 4703 | .catch((err) => logger.error(err)) 4704 | } 4705 | ``` 4706 | 4707 | 4708 | **Answer:** 4709 | ```js 4710 | async function asyncTask() { 4711 | try { 4712 | const valueA = await functionA() 4713 | const valueB = await functionB(valueA) 4714 | const valueC = await functionC(valueB) 4715 | return await functionD(valueC) 4716 | } catch (err) { 4717 | logger.error(err) 4718 | } 4719 | } 4720 | ``` 4721 | 4722 | **Source:** _stackoverflow.com_ 4723 | 4724 | #### Q15: Are you familiar with differences between Node.js nodules and ES6 nodules? ⭐⭐⭐ 4725 | **Answer:** 4726 | The modules used in Node.js follow a module specification known as the **CommonJS** specification. The recent updates to the JavaScript programming language, in the form of ES6, specify changes to the language, adding things like new class syntax and a module system. This module system is different from Node.js modules. To import ES6 module, we'd use the ES6 `import` functionality. 4727 | 4728 | Now ES6 modules are incompatible with Node.js modules. This has to do with the way modules are loaded differently between the two formats. If you use a compiler like Babel, you can mix and match module formats. 4729 | 4730 | **Source:** _stackoverflow.com_ 4731 | 4732 | #### Q16: Name some of the events fired by streams. ⭐⭐⭐⭐ 4733 | **Answer:** 4734 | Read Full Answer on 👉 FullStack.Cafe 4735 | 4736 | #### Q17: What's a stub? Name a use case. ⭐⭐⭐⭐ 4737 | **Answer:** 4738 | Read Full Answer on 👉 FullStack.Cafe 4739 | 4740 | #### Q18: Is Node.js entirely based on a single-thread? ⭐⭐⭐⭐ 4741 | **Answer:** 4742 | Read Full Answer on 👉 FullStack.Cafe 4743 | 4744 | #### Q19: When to not use Node.js? ⭐⭐⭐⭐ 4745 | **Answer:** 4746 | Read Full Answer on 👉 FullStack.Cafe 4747 | 4748 | #### Q20: What are the timing features of Node.js? ⭐⭐⭐⭐ 4749 | **Answer:** 4750 | Read Full Answer on 👉 FullStack.Cafe 4751 | 4752 | #### Q21: How would you handle errors for async code in Node.js? ⭐⭐⭐⭐ 4753 | **Answer:** 4754 | Read Full Answer on 👉 FullStack.Cafe 4755 | 4756 | #### Q22: How do you convert an existing callback API to promises? ⭐⭐⭐⭐ 4757 | **Details:** 4758 | How to convert this callback code to Promise? Provide some examples. 4759 | ```js 4760 | function divisionAPI (number, divider, successCallback, errorCallback) { 4761 | if (divider == 0) { 4762 | return errorCallback( new Error("Division by zero") ) 4763 | } 4764 | successCallback( number / divider ) 4765 | } 4766 | ``` 4767 | 4768 | **Answer:** 4769 | Read Full Answer on 👉 FullStack.Cafe 4770 | 4771 | #### Q23: Can Node.js work without V8? ⭐⭐⭐⭐ 4772 | **Answer:** 4773 | Read Full Answer on 👉 FullStack.Cafe 4774 | 4775 | #### Q24: Is it possible to use "Class" in Node.js? ⭐⭐⭐⭐ 4776 | **Answer:** 4777 | Read Full Answer on 👉 FullStack.Cafe 4778 | 4779 | #### Q25: Can Node.js use other engines than V8? ⭐⭐⭐⭐⭐ 4780 | **Answer:** 4781 | Read Full Answer on 👉 FullStack.Cafe 4782 | 4783 | #### Q26: What is the difference between process.nextTick() and setImmediate() ? ⭐⭐⭐⭐⭐ 4784 | **Answer:** 4785 | Read Full Answer on 👉 FullStack.Cafe 4786 | 4787 | #### Q27: Explain what is Reactor Pattern in Node.js? ⭐⭐⭐⭐⭐ 4788 | **Answer:** 4789 | Read Full Answer on 👉 FullStack.Cafe 4790 | 4791 | #### Q28: Why should you separate Express 'app' and 'server'? ⭐⭐⭐⭐⭐ 4792 | **Answer:** 4793 | Read Full Answer on 👉 FullStack.Cafe 4794 | 4795 | #### Q29: How many threads does Node actually create? ⭐⭐⭐⭐⭐ 4796 | **Answer:** 4797 | Read Full Answer on 👉 FullStack.Cafe 4798 | 4799 | #### Q30: How V8 compiles JavaScript code? ⭐⭐⭐⭐⭐ 4800 | **Answer:** 4801 | Read Full Answer on 👉 FullStack.Cafe 4802 | 4803 | #### Q31: What is V8 Templates? ⭐⭐⭐⭐⭐ 4804 | **Answer:** 4805 | Read Full Answer on 👉 FullStack.Cafe 4806 | 4807 | #### Q32: Why Node.js devs tend to lean towards the Module Requiring vs Dependency Injection? ⭐⭐⭐⭐⭐ 4808 | **Answer:** 4809 | Read Full Answer on 👉 FullStack.Cafe 4810 | 4811 | #### Q33: What will happen when that code will be executed? ⭐⭐⭐⭐⭐ 4812 | **Details:** 4813 | 4814 | What will happen when that code will be executed? 4815 | ```js 4816 | var EventEmitter = require('events'); 4817 | 4818 | var crazy = new EventEmitter(); 4819 | 4820 | crazy.on('event1', function () { 4821 | console.log('event1 fired!'); 4822 | process.nextTick(function () { 4823 | crazy.emit('event2'); 4824 | }); 4825 | }); 4826 | 4827 | crazy.on('event2', function () { 4828 | console.log('event2 fired!'); 4829 | process.nextTick(function () { 4830 | crazy.emit('event3'); 4831 | }); 4832 | 4833 | }); 4834 | 4835 | crazy.on('event3', function () { 4836 | console.log('event3 fired!'); 4837 | process.nextTick(function () { 4838 | crazy.emit('event1'); 4839 | }); 4840 | }); 4841 | 4842 | crazy.emit('event1'); 4843 | ``` 4844 | 4845 | **Answer:** 4846 | Read Full Answer on 👉 FullStack.Cafe 4847 | 4848 | ## [[⬆]](#toc) 35 LINQ Interview Questions and Answers in 2019 4849 | > Originally published on 👉 35 LINQ Interview Questions and Answers in 2019 | FullStack.Cafe 4850 | 4851 | #### Q1: What is LINQ? ⭐ 4852 | **Answer:** 4853 | **LINQ** stands for Language INtegrated Query. LINQ allows us to write queries over local collection objects and remote data sources like SQL, XML documents etc. We can write LINQ query on any collection class which implements the `IEnumerable` interface. 4854 | 4855 | **Source:** _stackoverflow.com_ 4856 | 4857 | #### Q2: What are the types of LINQ? ⭐ 4858 | **Answer:** 4859 | * LINQ to Objects 4860 | * LINQ to XML 4861 | * LINQ to Dataset 4862 | * LINQ to SQL 4863 | * LINQ to Entities 4864 | 4865 | **Source:** _career.guru99.com_ 4866 | 4867 | #### Q3: Explain what is LINQ? Why is it required? ⭐ 4868 | **Answer:** 4869 | **Language Integrated Query** or **LINQ** is the collection of standard query operators which provides query facilities into.NET framework language like C#, VB.NET. LINQ is required as it bridges the gap between the world of data and the world of objects. 4870 | 4871 | **Source:** _career.guru99.com_ 4872 | 4873 | #### Q4: List out the three main components of LINQ? ⭐⭐ 4874 | **Answer:** 4875 | Three main components of LINQ are 4876 | 4877 | * Standard Query Operators 4878 | * Language Extensions 4879 | * LINQ Providers 4880 | 4881 | **Source:** _career.guru99.com_ 4882 | 4883 | #### Q5: What is Anonymous function? ⭐⭐ 4884 | **Answer:** 4885 | An Anonymous function is a special function which does not have any name. We just define their parameters and define the code into the curly braces. 4886 | 4887 | Consider: 4888 | ```csharp 4889 | delegate int func(int a, int b); 4890 | static void Main(string[] args) 4891 | { 4892 | func f1 = delegate(int a, int b) 4893 | { 4894 | return a + b; 4895 | }; 4896 | 4897 | Console.WriteLine(f1(1, 2)); 4898 | } 4899 | ``` 4900 | 4901 | **Source:** _stackoverflow.com_ 4902 | 4903 | #### Q6: What are Anonymous Types? ⭐⭐ 4904 | **Answer:** 4905 | Anonymous types are types that are generated by compiler at run time. When we create a anonymous type we do not specify a name. We just write properties names and their values. Compiler at runtime create these properties and assign values to them. 4906 | 4907 | ```csharp 4908 | var k = new { FirstProperty = "value1", SecondProperty = "value2" }; 4909 | Console.WriteLine(k.FirstProperty); 4910 | ``` 4911 | 4912 | Anonymous class is useful in LINQ queries to save our intermediate results. 4913 | 4914 | There are some restrictions on Anonymous types as well: 4915 | 4916 | * Anonymous types can not implement interfaces. 4917 | * Anonymous types can not specify any methods. 4918 | * We can not define static members. 4919 | * All defined properties must be initialized. 4920 | * We can only define public fields. 4921 | 4922 | **Source:** _stackoverflow.com_ 4923 | 4924 | #### Q7: What are Extension Methods? ⭐⭐ 4925 | **Answer:** 4926 | **Extension methods** are static functions of a static class. These methods can be invoked just like instance method syntax. These methods are useful when we can not want to modify the class. Consider: 4927 | 4928 | ```csharp 4929 | public static class StringMethods 4930 | { 4931 | public static bool IsStartWithLetterM(this string s) 4932 | { 4933 | return s.StartsWith("m"); 4934 | } 4935 | } 4936 | class Program 4937 | { 4938 | static void Main(string[] args) 4939 | { 4940 | string value = "malslfds"; 4941 | Console.WriteLine(value.IsStartWithLetterM()); //print true; 4942 | 4943 | Console.ReadLine(); 4944 | } 4945 | } 4946 | ``` 4947 | 4948 | **Source:** _stackoverflow.com_ 4949 | 4950 | #### Q8: Explain what is “LINQ to Objects”? ⭐⭐ 4951 | **Answer:** 4952 | When LINQ queries any `IEnumerable()` collection or IEnumerable directly without the use of an intermediate LINQ provider or API such as LINQ to SQL or LINQ to XML is referred as **LINQ to Objects**. 4953 | 4954 | **Source:** _career.guru99.com_ 4955 | 4956 | #### Q9: Explain what is the purpose of LINQ providers in LINQ? ⭐⭐ 4957 | **Answer:** 4958 | LINQ providers are set of classes that take an LINQ query which generates method that executes an equivalent query against a particular data source. 4959 | 4960 | **Source:** _career.guru99.com_ 4961 | 4962 | #### Q10: Mention what is the role of DataContext classes in LINQ? ⭐⭐ 4963 | **Answer:** 4964 | **DataContext** class acts as a bridge between SQL Server database and the LINQ to SQL. For accessing the database and also for changing the data in the database, it contains connections string and the functions. Essentially a DataContext class performs the following three tasks: 4965 | 4966 | * Create connection to database. 4967 | * It submits and retrieves object to database. 4968 | * Converts objects to SQL queries and vice versa. 4969 | 4970 | **Source:** _career.guru99.com_ 4971 | 4972 | #### Q11: In LINQ how will you find the index of the element using where() with Lambda Expressions? ⭐⭐ 4973 | **Answer:** 4974 | In order to find the index of the element use the overloaded version of `where()` with the lambda expression: 4975 | 4976 | ```csharp 4977 | where(( i, ix ) => i == ix); 4978 | ``` 4979 | 4980 | **Source:** _career.guru99.com_ 4981 | 4982 | #### Q12: Explain how LINQ is useful than Stored Procedures? ⭐⭐ 4983 | **Answer:** 4984 | * **Debugging:** It is difficult to debug a stored procedure but as LINQ is part of.NET, visual studio debugger can be used to debug the queries 4985 | * **Deployment:** For stored procedure, additional script should be provided but with LINQ everything gets compiled into single DLL hence deployment becomes easy 4986 | * **Type Safety:** LINQ is type safe, so queries errors are type checked at compile time 4987 | 4988 | **Source:** _career.guru99.com_ 4989 | 4990 | #### Q13: Explain why SELECT clause comes after FROM clause in LINQ? ⭐⭐ 4991 | **Answer:** 4992 | With other programming language and C#, LINQ is used, it requires all the variables to be declared first. “FROM” clause of LINQ query defines the range or conditions to select records. So, FROM clause must appear before SELECT in LINQ. 4993 | 4994 | **Source:** _career.guru99.com_ 4995 | 4996 | #### Q14: Could you compare Entity Framework vs LINQ to SQL vs ADO.NET with stored procedures? ⭐⭐⭐ 4997 | **Answer:** 4998 | **Stored procedures:** 4999 | 5000 | (++) 5001 | 5002 | - Great flexibility 5003 | - Full control over SQL 5004 | - The highest performance available 5005 | 5006 | (--) 5007 | 5008 | - Requires knowledge of SQL 5009 | - Stored procedures are out of source control (harder to test) 5010 | - Substantial amount of "repeating yourself" while specifying the same table and field names. The high chance of breaking the application after renaming a DB entity and missing some references to it somewhere. 5011 | - Slow development 5012 | 5013 | **ORM (EF, L2SQL, ADO.NET):** 5014 | 5015 | (++) 5016 | 5017 | - Rapid development 5018 | - Data access code now under source control 5019 | - You're isolated from changes in DB. If that happens you only need to update your model/mappings in one place. 5020 | 5021 | (--) 5022 | 5023 | - Performance may be worse 5024 | - No or little control over SQL the ORM produces (could be inefficient or worse buggy). Might need to intervene and replace it with custom stored procedures. That will render your code messy (some LINQ in code, some SQL in code and/or in the DB out of source control). 5025 | - As any abstraction can produce "high-level" developers having no idea how it works under the hood 5026 | 5027 | **Source:** _stackoverflow.com_ 5028 | 5029 | #### Q15: When trying to decide between using the Entity Framework and LINQ to SQL as an ORM, what's the difference? ⭐⭐⭐ 5030 | **Answer:** 5031 | * **LINQ to SQL** only supports 1 to 1 mapping of database tables, views, sprocs and functions available in Microsoft SQL Server. It's a great API to use for quick data access construction to relatively well designed SQL Server databases. LINQ2SQL was first released with C# 3.0 and .Net Framework 3.5. 5032 | 5033 | * **LINQ to Entities** (ADO.Net Entity Framework) is an ORM (Object Relational Mapper) API which allows for a broad definition of object domain models and their relationships to many different ADO.Net data providers. As such, you can mix and match a number of different database vendors, application servers or protocols to design an aggregated mash-up of objects which are constructed from a variety of tables, sources, services, etc. ADO.Net Framework was released with the .Net Framework 3.5 SP1. 5034 | 5035 | **Source:** _stackoverflow.com_ 5036 | 5037 | #### Q16: Using LINQ to remove elements from a List ⭐⭐⭐ 5038 | **Details:** 5039 | Given that `authorsList` is of type `List`, how can I delete the `Author` elements that are equalling to `Bob`? 5040 | 5041 | **Answer:** 5042 | Consider: 5043 | ```csharp 5044 | authorsList.RemoveAll(x => x.FirstName == "Bob"); 5045 | ``` 5046 | 5047 | **Source:** _stackoverflow.com_ 5048 | 5049 | #### Q17: What is the difference between First() and Take(1)? ⭐⭐⭐ 5050 | **Details:** 5051 | Consider: 5052 | ```csharp 5053 | var result = List.Where(x => x == "foo").First(); 5054 | var result = List.Where(x => x == "foo").Take(1); 5055 | ``` 5056 | 5057 | **Answer:** 5058 | The difference between `First()` and `Take()` is that `First()` returns the element itself, while `Take()` returns a sequence of elements that contains exactly one element. (If you pass 1 as the parameter). 5059 | 5060 | **Source:** _stackoverflow.com_ 5061 | 5062 | #### Q18: When to use First() and when to use FirstOrDefault() with LINQ? ⭐⭐⭐ 5063 | **Answer:** 5064 | * Use `First()` when you know or expect the sequence to have at least one element. In other words, when it is an exceptional occurrence that the sequence is empty. 5065 | * Use `FirstOrDefault()` when you know that you will need to check whether there was an element or not. In other words, when it is legal for the sequence to be empty. You should not rely on exception handling for the check. (It is bad practice and might hurt performance). 5066 | 5067 | `First()` will throw an exception if there's no row to be returned, while `FirstOrDefault()` will return the default value (NULL for all reference types) instead. 5068 | 5069 | **Source:** _stackoverflow.com_ 5070 | 5071 | #### Q19: Explain how standard query operators useful in LINQ? ⭐⭐⭐ 5072 | **Answer:** 5073 | A set of extension methods forming a query pattern is known as LINQ Standard Query Operators. As building blocks of LINQ query expressions, these operators offer a range of query capabilities like filtering, sorting, projection, aggregation, etc. 5074 | 5075 | LINQ standard query operators can be categorized into the following ones on the basis of their functionality. 5076 | 5077 | * Filtering Operators (Where, OfType) 5078 | * Join Operators (Join, GroupJoin) 5079 | * Projection Operations (Select, SelectMany) 5080 | * Sorting Operators (OrderBy, ThenBy, Reverse, ...) 5081 | * Grouping Operators (GroupBy, ToLookup) 5082 | * Conversions (Cast, ToArray, ToList, ...) 5083 | * Concatenation (Concat) 5084 | * Aggregation (Aggregate, Average, Count, Max, ...) 5085 | * Quantifier Operations (All, Any, Contains) 5086 | * Partition Operations (Skip, SkipWhile, Take, ...) 5087 | * Generation Operations (DefaultIfEmpty, Empty, Range, Repeat) 5088 | * Set Operations (Distinct, Except, ...) 5089 | * Equality (SequenceEqual) 5090 | * Element Operators (ElementAt, First, Last, ...) 5091 | 5092 | **Source:** _tutorialspoint.com_ 5093 | 5094 | #### Q20: What is Expression Trees and how they used in LINQ? ⭐⭐⭐ 5095 | **Answer:** 5096 | An **Expression Tree** is a data structure that contains Expressions, which is basically code. So it is a tree structure that represents a calculation you may make in code. These pieces of code can then be executed by "running" the expression tree over a set of data. 5097 | 5098 | In LINQ, expression trees are used to represent structured queries that target sources of data that implement `IQueryable`. For example, the LINQ provider implements the `IQueryable` interface for querying relational data stores. The C# compiler compiles queries that target such data sources into code that builds an expression tree at runtime. The query provider can then traverse the expression tree data structure and translate it into a query language appropriate for the data source. 5099 | 5100 | **Source:** _docs.microsoft.com_ 5101 | 5102 | #### Q21: Could you explian what is the exact deference between deferred execution and Lazy evaluation in C#? ⭐⭐⭐ 5103 | **Answer:** 5104 | In practice, they mean essentially the same thing. However, it's preferable to use the term deferred. 5105 | 5106 | * Lazy means "don't do the work until you absolutely have to." 5107 | * Deferred means "don't compute the result until the caller actually uses it." 5108 | 5109 | When the caller decides to use the result of an evaluation (i.e. start iterating through an `IEnumerable`), that is precisely the point at which the "work" needs to be done (such as issuing a query to the database). 5110 | 5111 | The term _deferred_ is more specific/descriptive as to what's actually going on. When I say that I am lazy, it means that I avoid doing unnecessary work; it's ambiguous as to what that really implies. However, when I say that execution/evaluation is deferred, it essentially means that I am not giving you the real result at all, but rather a ticket you can use to claim the result. I defer actually going out and getting that result until you claim it. 5112 | 5113 | **Source:** _stackoverflow.com_ 5114 | 5115 | #### Q22: Explain what are LINQ compiled queries? ⭐⭐⭐ 5116 | **Answer:** 5117 | There may be scenario where we need to execute a particular query many times and repeatedly. LINQ allows us to make this task very easy by enabling us to create a query and make it compiled always. Benefits of Compiled Queries: 5118 | 5119 | * Query does need to compiled each time so execution of the query is fast. 5120 | * Query is compiled once and can be used any number of times. 5121 | * Query does need to be recompiled even if the parameter of the query is being changed. 5122 | 5123 | Consider: 5124 | ```csharp 5125 | static class MyCompliedQueries { 5126 | public static Func > CompliedQueryForPerson = 5127 | CompiledQuery.Compile((DataClasses1DataContext context) = >from c in context.Persons select c); 5128 | } 5129 | ``` 5130 | 5131 | **Source:** _career.guru99.com_ 5132 | 5133 | #### Q23: Get the indexes of top n items where item value = true ⭐⭐⭐ 5134 | **Details:** 5135 | I have a `List`. I need to get the indexes of top n items where item `value = true`. 5136 | 5137 | ```csharp 5138 | 10011001000 5139 | 5140 | TopTrueIndexes(3) = The first 3 indexes where bits are true are 0, 3, 4 5141 | TopTrueIndexes(4) = The first 4 indexes where bits are true are 0, 3, 4, 7 5142 | ``` 5143 | 5144 | 5145 | **Answer:** 5146 | Assuming you have some easily-identifiable condition, you can do something like this, which will work for any `IEnumerable`: 5147 | ```csharp 5148 | var query = source.Select((value, index) => new { value, index }) 5149 | .Where(x => x.value => Condition(value)) 5150 | .Select(x => x.index) 5151 | .Take(n); 5152 | ``` 5153 | The important bits are that you use the overload of `Select` to get index/value pairs before the Where, and then another Select to get just the indexes after the Where... and use Take to only get the first n results. 5154 | 5155 | **Source:** _stackoverflow.com_ 5156 | 5157 | #### Q24: Define what is Let clause? ⭐⭐⭐ 5158 | **Answer:** 5159 | In a query expression, it is sometimes useful to store the result of a sub-expression in order to use it in subsequent clauses. You can do this with the `let` keyword, which creates a new range variable and initializes it with the result of the expression you supply. 5160 | 5161 | Consider: 5162 | ```csharp 5163 | var names = new string[] { "Dog", "Cat", "Giraffe", "Monkey", "Tortoise" }; 5164 | var result = 5165 | from animalName in names 5166 | let nameLength = animalName.Length 5167 | where nameLength > 3 5168 | orderby nameLength 5169 | select animalName; 5170 | ``` 5171 | 5172 | **Source:** _career.guru99.com_ 5173 | 5174 | #### Q25: Explain what is the difference between Skip() and SkipWhile() extension method? ⭐⭐⭐ 5175 | **Answer:** 5176 | * **Skip()** **:** It will take an integer argument and from the given `IEnumerable` it skips the top `n` numbers 5177 | * **SkipWhile ():** It will continue to skip the elements as far as the input condition is `true`. It will return all remaining elements if the condition is `false`. 5178 | 5179 | **Source:** _career.guru99.com_ 5180 | 5181 | #### Q26: Explain what is lambda expressions in LINQ? ⭐⭐⭐ 5182 | **Answer:** 5183 | **Lambda expression** is referred as a unique function use to form delegates or expression tree types, where right side is the output and left side is the input to the method. For writing LINQ queries particularly, Lambda expression is used. 5184 | 5185 | **Source:** _career.guru99.com_ 5186 | 5187 | #### Q27: Name some advantages of LINQ over Stored Procedures ⭐⭐⭐⭐ 5188 | **Answer:** 5189 | Read Full Answer on 👉 FullStack.Cafe 5190 | 5191 | #### Q28: What are the benefits of a Deferred Execution in LINQ? ⭐⭐⭐⭐ 5192 | **Answer:** 5193 | Read Full Answer on 👉 FullStack.Cafe 5194 | 5195 | #### Q29: When should I use a CompiledQuery? ⭐⭐⭐⭐ 5196 | **Answer:** 5197 | Read Full Answer on 👉 FullStack.Cafe 5198 | 5199 | #### Q30: What is an equivalent to the "let" keyword in chained LINQ extension method calls? ⭐⭐⭐⭐ 5200 | **Answer:** 5201 | Read Full Answer on 👉 FullStack.Cafe 5202 | 5203 | #### Q31: Can you provide a concise distinction between anonymous method and lambda expressions? ⭐⭐⭐⭐⭐ 5204 | **Answer:** 5205 | Read Full Answer on 👉 FullStack.Cafe 5206 | 5207 | #### Q32: Name some disadvantages of LINQ over sprocs ⭐⭐⭐⭐⭐ 5208 | **Answer:** 5209 | Read Full Answer on 👉 FullStack.Cafe 5210 | 5211 | #### Q33: What is the difference between Select and SelectMany? ⭐⭐⭐⭐⭐ 5212 | **Answer:** 5213 | Read Full Answer on 👉 FullStack.Cafe 5214 | 5215 | #### Q34: What is the difference between returning IQueryable vs. IEnumerable? ⭐⭐⭐⭐⭐ 5216 | **Details:** 5217 | What is the difference between returning `IQueryable` vs. `IEnumerable`? 5218 | 5219 | ```csharp 5220 | IQueryable < Customer > custs = from c in db.Customers 5221 | where c.City == "" 5222 | select c; 5223 | 5224 | IEnumerable < Customer > custs = from c in db.Customers 5225 | where c.City == "" 5226 | select c; 5227 | ``` 5228 | 5229 | Will both be deferred execution and when should one be preferred over the other? 5230 | 5231 | **Answer:** 5232 | Read Full Answer on 👉 FullStack.Cafe 5233 | 5234 | #### Q35: Why use .AsEnumerable() rather than casting to IEnumerable? ⭐⭐⭐⭐⭐ 5235 | **Answer:** 5236 | Read Full Answer on 👉 FullStack.Cafe 5237 | 5238 | ## [[⬆]](#toc) 35 Microservices Interview Questions You Most Likely Can't Answer 5239 | > Originally published on 👉 35 Microservices Interview Questions You Most Likely Can't Answer | FullStack.Cafe 5240 | 5241 | #### Q1: What is meant by Continuous Integration? ⭐ 5242 | **Answer:** 5243 | *Continuous Integration (CI)* is a development practice that requires developers to integrate code into a shared repository several times a day. Each check-in is then verified by an automated build, allowing teams to detect problems early. 5244 | 5245 | **Source:** _edureka.co_ 5246 | 5247 | #### Q2: What does Containerization mean? ⭐⭐ 5248 | **Answer:** 5249 | *Containerisation* is a type of *virtualization* strategy that emerged as an alternative to traditional hypervisor-based virtualization. 5250 | 5251 | In containerization, the operating system is shared by the different containers rather than cloned for each virtual machine. For example Docker provides a container virtualization platform that serves as a good alternative to hypervisor-based arrangements. 5252 | 5253 | **Source:** _linoxide.com_ 5254 | 5255 | #### Q3: Explain Blue-Green Deployment Technique ⭐⭐⭐ 5256 | **Answer:** 5257 | **Blue-green deployment** is a technique that reduces downtime and risk by running two identical production environments called Blue and Green. At any time, only one of the environments is live, with the live environment serving all production traffic. For this example, Blue is currently live and Green is idle. 5258 | 5259 | As you prepare a new version of your software, deployment and the final stage of testing takes place in the environment that is not live: in this example, Green. Once you have deployed and fully tested the software in Green, you switch the router so all incoming requests now go to Green instead of Blue. Green is now live, and Blue is idle. 5260 | 5261 | This technique can eliminate downtime due to application deployment. In addition, blue-green deployment reduces risk: if something unexpected happens with your new version on Green, you can immediately roll back to the last version by switching back to Blue. 5262 | 5263 | **Source:** _cloudfoundry.org_ 5264 | 5265 | #### Q4: What's the difference between a blue/green deployment and a rolling deployment? ⭐⭐⭐ 5266 | **Answer:** 5267 | * In **Blue Green Deployment**, you have TWO complete environments. 5268 | One is Blue environment which is running and the Green environment to which you want to upgrade. Once you swap the environment from blue to green, the traffic is directed to your new green environment. You can delete or save your old blue environment for backup until the green environment is stable. 5269 | 5270 | * In **Rolling Deployment**, you have only ONE complete environment. The code is deployed in the subset of instances of the same environment and moves to another subset after completion. 5271 | 5272 | **Source:** _stackoverflow.com_ 5273 | 5274 | #### Q5: What are the differences between continuous integration, continuous delivery, and continuous deployment? ⭐⭐⭐ 5275 | **Answer:** 5276 | * Developers practicing **continuous integration** merge their changes back to the main branch as often as possible. By doing so, you avoid the integration hell that usually happens when people wait for release day to merge their changes into the release branch. 5277 | * **Continuous delivery** is an extension of continuous integration to make sure that you can release new changes to your customers quickly in a sustainable way. This means that on top of having automated your testing, you also have automated your release process and you can deploy your application at any point of time by clicking on a button. 5278 | * **Continuous deployment** goes one step further than continuous delivery. With this practice, every change that passes all stages of your production pipeline is released to your customers. There's no human intervention, and only a failed test will prevent a new change to be deployed to production. 5279 | 5280 | **Source:** _atlassian.com_ 5281 | 5282 | #### Q6: What do you know about serverless model? ⭐⭐⭐ 5283 | **Answer:** 5284 | **Serverless** refers to a model where the existence of servers is hidden from developers. It means you no longer have to deal with capacity, deployments, scaling and fault tolerance and OS. It will essentially reducing maintenance efforts and allow developers to quickly focus on developing codes. 5285 | 5286 | Examples are: 5287 | * Amazon AWS Lambda 5288 | * Azure Functions 5289 | 5290 | **Source:** _linoxide.com_ 5291 | 5292 | #### Q7: How is container different from a virtual machine? ⭐⭐⭐⭐ 5293 | **Answer:** 5294 | Read Full Answer on 👉 FullStack.Cafe 5295 | 5296 | #### Q8: What is Canary Releasing? ⭐⭐⭐⭐⭐ 5297 | **Answer:** 5298 | Read Full Answer on 👉 FullStack.Cafe 5299 | 5300 | #### Q9: What is Docker? ⭐ 5301 | **Answer:** 5302 | * Docker is a containerization platform which packages your application and all its dependencies together in the form of containers so as to ensure that your application works seamlessly in any environment be it development or test or production. 5303 | * Docker containers, wrap a piece of software in a complete filesystem that contains everything needed to run: code, runtime, system tools, system libraries etc. anything that can be installed on a server. 5304 | * This guarantees that the software will always run the same, regardless of its environment. 5305 | 5306 | **Source:** _edureka.co_ 5307 | 5308 | #### Q10: How virtualization works at low level? ⭐⭐⭐⭐ 5309 | **Answer:** 5310 | Read Full Answer on 👉 FullStack.Cafe 5311 | 5312 | #### Q11: What is Paravirtualization? ⭐⭐⭐⭐ 5313 | **Answer:** 5314 | Read Full Answer on 👉 FullStack.Cafe 5315 | 5316 | #### Q12: Define Microservice Architecture ⭐⭐ 5317 | **Answer:** 5318 | **Microservices**, aka **_Microservice Architecture_**, is an architectural style that structures an application as a collection of small autonomous services, modeled around a **business domain.** 5319 | 5320 | **Source:** _lambdatest.com_ 5321 | 5322 | #### Q13: What are the features of Microservices? ⭐⭐⭐ 5323 | **Answer:** 5324 | * **Decoupling** – Services within a system are largely decoupled. So the application as a whole can be easily built, altered, and scaled 5325 | * **Componentization** – Microservices are treated as independent components that can be easily replaced and upgraded 5326 | * **Business Capabilities** – Microservices are very simple and focus on a single capability 5327 | * **Autonomy** – Developers and teams can work independently of each other, thus increasing speed 5328 | * **Continous** **Delivery** – Allows frequent releases of software, through systematic automation of software creation, testing, and approval 5329 | * **Responsibility** – Microservices do not focus on applications as projects. Instead, they treat applications as products for which they are responsible 5330 | * **Decentralized Governance** – The focus is on using the right tool for the right job. That means there is no standardized pattern or any technology pattern. Developers have the freedom to choose the best useful tools to solve their problems 5331 | * **Agility** – Microservices support agile development. Any new feature can be quickly developed and discarded again 5332 | 5333 | **Source:** _lambdatest.com_ 5334 | 5335 | #### Q14: How does Microservice Architecture work? ⭐⭐⭐ 5336 | **Answer:** 5337 | * **Clients** – Different users from various devices send requests. 5338 | * **Identity Providers** – Authenticates user or clients identities and issues security tokens. 5339 | * **API Gateway** – Handles client requests. 5340 | * **Static Content** – Houses all the content of the system. 5341 | * **Management** – Balances services on nodes and identifies failures. 5342 | * **Service Discovery** – A guide to find the route of communication between microservices. 5343 | * **Content Delivery Networks** – Distributed network of proxy servers and their data centers. 5344 | * **Remote Service** – Enables the remote access information that resides on a network of IT devices. 5345 | 5346 | 5347 |

5348 |

5349 |

5350 | 5351 | 5352 | **Source:** _edureka.co_ 5353 | 5354 | #### Q15: What is the difference between Monolithic, SOA and Microservices Architecture? ⭐⭐⭐ 5355 | **Answer:** 5356 | * **Monolithic Architecture** is similar to a big container wherein all the software components of an application are assembled together and tightly packaged. 5357 | * A **Service-Oriented Architecture** is a collection of services which communicate with each other. The communication can involve either simple data passing or it could involve two or more services coordinating some activity. 5358 | * **Microservice Architecture** is an architectural style that structures an application as a collection of small autonomous services, modeled around a business domain. 5359 | 5360 | **Source:** _edureka.co_ 5361 | 5362 | #### Q16: What are main differences between Microservices and Monolithic Architecture? ⭐⭐⭐ 5363 | **Answer:** 5364 | **Microservices** 5365 | * Service Startup is fast 5366 | * Microservices are loosely coupled architecture. 5367 | * Changes done in a single data model does not affect other Microservices. 5368 | * Microservices focuses on products, not projects 5369 | 5370 | **Monolithic Architecture** 5371 | * Service startup takes time 5372 | * Monolithic architecture is mostly tightly coupled. 5373 | * Any changes in the data model affect the entire database 5374 | * Monolithic put emphasize over the whole project 5375 | 5376 | **Source:** _edureka.co_ 5377 | 5378 | #### Q17: What are the standard patterns of orchestrating microservices? ⭐⭐⭐ 5379 | **Answer:** 5380 | As we start to model more and more complex logic, we have to deal with the problem of managing business processes that stretch across the boundary of individual services. 5381 | 5382 | * With **orchestration**, we rely on a central brain to guide and drive the process, much like the conductor in an orchestra. The orchestration style corresponds more to the SOA idea of orchestration/task services. For example we could wrap the business flow in its own service. Where the proxy orchestrates the interaction between the microservices like shown in the below picture. 5383 | 5384 | * With **choreography**, we inform each part of the system of its job, and let it work out the details, like dancers all find‐ ing their way and reacting to others around them in a ballet. The choreography style corresponds to the dumb pipes and smart endpoints mentioned by Martin Fowler's. That approach is also called the **domain approach** and is using domain events, where each service publish events regarding what have happened and other services can subscribe to those events. 5385 | 5386 | 5387 | **Source:** _stackoverflow.com_ 5388 | 5389 | #### Q18: What are smart endpoints and dumb pipes? ⭐⭐⭐ 5390 | **Answer:** 5391 | * **Smart endpoints** just meaning actual business rules and any other validations happens behind those endpoints which are not visible to anyone to the consumers of those endpoints think of it as a place where actual Magic happens. 5392 | 5393 | * **Dumb pipelines** means any communication means where no further actions e.g validations are taken place, it simply carries the data across that particular channel and it may also be replaceable if need be. The infrastructure chosen is typically dumb (dumb as in acts as a message router only). It just means that routing is the only function the pipes should be doing. 5394 | 5395 | **Source:** _stackoverflow.com_ 5396 | 5397 | #### Q19: Whether do you find GraphQL the right fit for designing microservice architecture? ⭐⭐⭐ 5398 | **Answer:** 5399 | _GraphQL and microservices are a perfect fit_, because GraphQL hides the fact that you have a microservice architecture from the clients. From a backend perspective, you want to split everything into microservices, but from a frontend perspective, you would like all your data to come from a single API. Using GraphQL is the best way I know of that lets you do both. It lets you split up your backend into microservices, while still providing a single API to all your application, and allowing joins across data from different services. 5400 | 5401 | 5402 |

5403 |

5404 |

The hero's birthday is {{ birthday | date }}

5483 | ``` 5484 | In this page, you'll use pipes to transform a component's birthday property into a human-friendly date. 5485 | 5486 | **Source:** _angular.io_ 5487 | 5488 | #### Q2: What is the minimum definition of a component? ⭐⭐ 5489 | **Answer:** 5490 | The absolute minimal configuration for a `@Component` in Angular is a template. Both template properties are set to optional because you have to define either `template` or `templateUrl`. 5491 | 5492 | When you don't define them, you will get an exception like this: 5493 | ```sh 5494 | No template specified for component 'ComponentName' 5495 | ``` 5496 | A selector property is not required, as you can also use your components in a route. 5497 | 5498 | **Source:** _stackoverflow.com_ 5499 | 5500 | #### Q3: What's the difference between an Angular component and module? ⭐⭐ 5501 | **Answer:** 5502 | *Components* control views (html). They also communicate with other components and services to bring functionality to your app. 5503 | 5504 | *Modules* consist of one or more components. They do not control any html. Your modules declare which components can be used by components belonging to other modules, which classes will be injected by the dependency injector and which component gets bootstrapped. Modules allow you to manage your components to bring modularity to your app. 5505 | 5506 | **Source:** _stackoverflow.com_ 5507 | 5508 | #### Q4: How can I select an element in a component template? ⭐⭐ 5509 | **Answer:** 5510 | You can get a handle to the DOM element via ElementRef by injecting it into your component's constructor: 5511 | 5512 | ```js 5513 | constructor(myElement: ElementRef) { ... } 5514 | ``` 5515 | 5516 | **Source:** _medium.com_ 5517 | 5518 | #### Q5: What is an observer? ⭐⭐ 5519 | **Answer:** 5520 | Observer is an interface for a consumer of push-based notifications delivered by an Observable. It has below structure, 5521 | ```javascript 5522 | interface Observer { 5523 | closed?: boolean; 5524 | next: (value: T) => void; 5525 | error: (err: any) => void; 5526 | complete: () => void; 5527 | } 5528 | ``` 5529 | A handler that implements the Observer interface for receiving observable notifications will be passed as a parameter for observable as below, 5530 | ```javascript 5531 | myObservable.subscribe(myObserver); 5532 | ``` 5533 | **Note:** If you don't supply a handler for a notification type, the observer ignores notifications of that type. 5534 | 5535 | **Source:** _github.com/sudheerj_ 5536 | 5537 | #### Q6: What is an observable? ⭐⭐ 5538 | **Answer:** 5539 | An Observable is a unique Object similar to a Promise that can help manage async code. Observables are not part of the JavaScript language so we need to rely on a popular Observable library called RxJS. 5540 | The observables are created using new keyword. Let see the simple example of observable, 5541 | ```javascript 5542 | import { Observable } from 'rxjs'; 5543 | 5544 | const observable = new Observable(observer => { 5545 | setTimeout(() => { 5546 | observer.next('Hello from a Observable!'); 5547 | }, 2000); 5548 | });` 5549 | ``` 5550 | 5551 | **Source:** _github.com/sudheerj_ 5552 | 5553 | #### Q7: What is TestBed? ⭐⭐⭐ 5554 | **Answer:** 5555 | The **Angular Test Bed (ATB)** is a higher level *Angular Only* testing framework that allows us to easily test behaviours that depend on the Angular Framework. 5556 | 5557 | We still write our tests in Jasmine and run using Karma but we now have a slightly easier way to create components, handle injection, test asynchronous behaviour and interact with our application. 5558 | 5559 | The TestBed creates a dynamically-constructed Angular test module that emulates an Angular `@NgModule`. 5560 | 5561 | **Source:** _angular.io_ 5562 | 5563 | #### Q8: What is Redux and how does it relate to an Angular app? ⭐⭐⭐ 5564 | **Answer:** 5565 | **Redux** is a way to manage application state and improve maintainability of asynchronicity in your application by providing a single source of truth for the application state, and a unidirectional flow of data change in the application. `ngrx/store` is one implementation of Redux principles. 5566 | 5567 | **Source:** _github.com/WebPredict_ 5568 | 5569 | #### Q9: What are the Core Dependencies of Angular 7? ⭐⭐⭐ 5570 | **Answer:** 5571 | There are two types of core dependencies, RxJS and TypeScript. 5572 | 5573 | * **RxJS 6.3** - RxJS version 6.3 is used by Angular 7. It has no changes in the version from Angular 6 5574 | 5575 | * **TypeScript 3.1** - TypeScript version 3.1 is used by Angular 7. It is the upgrade from the version 2.9 of Angular 6. 5576 | 5577 | **Source:** _onlineinterviewquestions.com_ 5578 | 5579 | #### Q10: Why Incremental DOM Has Low Memory Footprint? ⭐⭐⭐ 5580 | **Answer:** 5581 | Virtual DOM creates a whole tree from scratch every time you rerender. 5582 | 5583 | Incremental DOM, on the other hand, doesn’t need any memory to rerender the view if it doesn’t change the DOM. We only have to allocate the memory when the DOM nodes are added or removed. And the size of the allocation is proportional to the size of the DOM change. 5584 | 5585 | **Source:** _blog.nrwl.io_ 5586 | 5587 | #### Q11: What are the ways to control AOT compilation? ⭐⭐⭐ 5588 | **Answer:** 5589 | You can control your app compilation in two ways 5590 | 1. By providing template compiler options in the `tsconfig.json` file 5591 | 2. By configuring Angular metadata with decorators 5592 | 5593 | **Source:** _github.com/sudheerj_ 5594 | 5595 | #### Q12: What is activated route? ⭐⭐⭐ 5596 | **Answer:** 5597 | **ActivatedRoute** contains the information about a route associated with a component loaded in an outlet. It can also be used to traverse the router state tree. The ActivatedRoute will be injected as a router service to access the information. In the below example, you can access route path and parameters, 5598 | 5599 | ```js 5600 | @Component({ 5601 | ... 5602 | }) 5603 | class MyComponent { 5604 | constructor(route: ActivatedRoute) { 5605 | const id: Observable < string > = route.params.pipe(map(p => p.id)); 5606 | const url: Observable < string > = route.url.pipe(map(segments => segments.join(''))); 5607 | // route.data includes both `data` and `resolve` 5608 | const user = route.data.pipe(map(d => d.user)); 5609 | } 5610 | } 5611 | ``` 5612 | 5613 | 5614 | **Source:** _github.com/sudheerj_ 5615 | 5616 | #### Q13: What is router outlet? ⭐⭐⭐ 5617 | **Answer:** 5618 | The **RouterOutlet** is a directive from the router library and it acts as a placeholder that marks the spot in the template where the router should display the components for that outlet. Router outlet is used as a component, 5619 | ```html 5620 | 5621 | 5622 | ``` 5623 | 5624 | **Source:** _github.com/sudheerj_ 5625 | 5626 | #### Q14: What are the utility functions provided by RxJS? ⭐⭐⭐ 5627 | **Answer:** 5628 | The RxJS library also provides below utility functions for creating and working with observables. 5629 | 1. Converting existing code for async operations into observables 5630 | 2. Iterating through the values in a stream 5631 | 3. Mapping values to different types 5632 | 4. Filtering streams 5633 | 5. Composing multiple streams 5634 | 5635 | **Source:** _github.com/sudheerj_ 5636 | 5637 | #### Q15: What is multicasting? ⭐⭐⭐ 5638 | **Answer:** 5639 | **Multi-casting** is the practice of broadcasting to a list of multiple subscribers in a single execution. Let's demonstrate the multi-casting feature, 5640 | ```javascript 5641 | var source = Rx.Observable.from([1, 2, 3]); 5642 | var subject = new Rx.Subject(); 5643 | var multicasted = source.multicast(subject); 5644 | 5645 | // These are, under the hood, `subject.subscribe({...})`: 5646 | multicasted.subscribe({ 5647 | next: (v) => console.log('observerA: ' + v) 5648 | }); 5649 | multicasted.subscribe({ 5650 | next: (v) => console.log('observerB: ' + v) 5651 | }); 5652 | 5653 | // This is, under the hood, `s 5654 | ``` 5655 | 5656 | **Source:** _github.com/sudheerj_ 5657 | 5658 | #### Q16: What is subscribing? ⭐⭐⭐ 5659 | **Answer:** 5660 | An Observable instance begins publishing values only when someone subscribes to it. So you need to subscribe by calling the **subscribe()** method of the instance, passing an observer object to receive the notifications. 5661 | 5662 | Let's take an example of creating and subscribing to a simple observable, with an observer that logs the received message to the console. 5663 | ```javascript 5664 | Creates an observable sequence of 5 integers, starting from 1 5665 | const source = range(1, 5); 5666 | 5667 | // Create observer object 5668 | const myObserver = { 5669 | next: x => console.log('Observer got a next value: ' + x), 5670 | error: err => console.error('Observer got an error: ' + err), 5671 | complete: () => console.log('Observer got a complete notification'), 5672 | }; 5673 | 5674 | // Execute with the observer object and Prints out each item 5675 | myObservable.subscribe(myObserver); 5676 | // => Observer got a next value: 1 5677 | // => Observer got a next value: 2 5678 | // => Observer got a next value: 3 5679 | // => Observer got a next value: 4 5680 | // => Observer got a next value: 5 5681 | // => Observer got a complete notification 5682 | ``` 5683 | 5684 | **Source:** _github.com/sudheerj_ 5685 | 5686 | #### Q17: How to set headers for every request in Angular? ⭐⭐⭐⭐ 5687 | **Answer:** 5688 | Read Full Answer on 👉 FullStack.Cafe 5689 | 5690 | #### Q18: Why would you use renderer methods instead of using native element methods? ⭐⭐⭐⭐ 5691 | **Answer:** 5692 | Read Full Answer on 👉 FullStack.Cafe 5693 | 5694 | #### Q19: What is Zone in Angular? ⭐⭐⭐⭐ 5695 | **Answer:** 5696 | Read Full Answer on 👉 FullStack.Cafe 5697 | 5698 | #### Q20: What does a just-in-time (JIT) compiler do (in general)? ⭐⭐⭐⭐ 5699 | **Answer:** 5700 | Read Full Answer on 👉 FullStack.Cafe 5701 | 5702 | #### Q21: What is ngUpgrage? ⭐⭐⭐⭐ 5703 | **Answer:** 5704 | Read Full Answer on 👉 FullStack.Cafe 5705 | 5706 | #### Q22: Why would you use lazy loading modules in Angular app? ⭐⭐⭐⭐ 5707 | **Answer:** 5708 | Read Full Answer on 👉 FullStack.Cafe 5709 | 5710 | #### Q23: What is Ivy Renderer? Is it supported by Angular 7? ⭐⭐⭐⭐ 5711 | **Answer:** 5712 | Read Full Answer on 👉 FullStack.Cafe 5713 | 5714 | #### Q24: What is incremental DOM? How is it different from virtual DOM? ⭐⭐⭐⭐ 5715 | **Answer:** 5716 | Read Full Answer on 👉 FullStack.Cafe 5717 | 5718 | #### Q25: What are the advantages with AOT? ⭐⭐⭐⭐ 5719 | **Answer:** 5720 | Read Full Answer on 👉 FullStack.Cafe 5721 | 5722 | #### Q26: Do I need to bootstrap custom elements? ⭐⭐⭐⭐ 5723 | **Answer:** 5724 | Read Full Answer on 👉 FullStack.Cafe 5725 | 5726 | #### Q27: What is the difference between pure and impure pipe? ⭐⭐⭐⭐ 5727 | **Answer:** 5728 | Read Full Answer on 👉 FullStack.Cafe 5729 | 5730 | #### Q28: What is the difference between BehaviorSubject vs Observable? ⭐⭐⭐⭐⭐ 5731 | **Answer:** 5732 | Read Full Answer on 👉 FullStack.Cafe 5733 | 5734 | #### Q29: What is the Angular equivalent to an AngularJS "$watch"? ⭐⭐⭐⭐⭐ 5735 | **Answer:** 5736 | Read Full Answer on 👉 FullStack.Cafe 5737 | 5738 | #### Q30: Name some differences between SystemJS vs WebPack? ⭐⭐⭐⭐⭐ 5739 | **Answer:** 5740 | Read Full Answer on 👉 FullStack.Cafe 5741 | 5742 | #### Q31: Just-in-Time (JiT) vs Ahead-of-Time (AoT) compilation. Explain the difference. ⭐⭐⭐⭐⭐ 5743 | **Answer:** 5744 | Read Full Answer on 👉 FullStack.Cafe 5745 | 5746 | #### Q32: Why angular uses url segment? ⭐⭐⭐⭐⭐ 5747 | **Answer:** 5748 | Read Full Answer on 👉 FullStack.Cafe 5749 | 5750 | #### Q33: Why did the Google team go with incremental DOM instead of virtual DOM? ⭐⭐⭐⭐⭐ 5751 | **Answer:** 5752 | Read Full Answer on 👉 FullStack.Cafe 5753 | 5754 | #### Q34: Why Incremental DOM is Tree Shakable? ⭐⭐⭐⭐⭐ 5755 | **Answer:** 5756 | Read Full Answer on 👉 FullStack.Cafe 5757 | 5758 | #### Q35: What's new in Angular 7? ⭐⭐⭐⭐⭐ 5759 | **Answer:** 5760 | Read Full Answer on 👉 FullStack.Cafe 5761 | 5762 | ## [[⬆]](#toc) 37 ASP.NET Interview Questions You Must Know 5763 | > Originally published on 👉 37 ASP.NET Interview Questions You Must Know | FullStack.Cafe 5764 | 5765 | #### Q1: What is ViewData? ⭐ 5766 | **Answer:** 5767 | Viewdata contains the key, value pairs as dictionary and this is derived from class — “ViewDataDictionary“. In action method we are setting the value for viewdata and in view the value will be fetched by typecasting. 5768 | 5769 | **Source:** _medium.com_ 5770 | 5771 | #### Q2: What is ASP.Net? ⭐ 5772 | **Answer:** 5773 | It is a framework developed by Microsoft on which we can develop new generation web sites using web forms(aspx), MVC, HTML, Javascript, CSS etc. Its successor of Microsoft Active Server Pages(ASP). Currently there is ASP.NET 4.0, which is used to develop web sites. There are various page extensions provided by Microsoft that are being used for web site development. Eg: aspx, asmx, ascx, ashx, cs, vb, html, XML etc. 5774 | 5775 | 5776 | **Source:** _guru99.com_ 5777 | 5778 | #### Q3: What is ASP.NET Core? ⭐⭐ 5779 | **Answer:** 5780 | ASP.NET Core is a brand new cross-platform web framework built with .NET Core framework. It is not an update to existing ASP.NET framework. It is a complete rewrite of the ASP.NET framework. It works with both .NET Core and .NET Framework. 5781 | 5782 | Main characterestics of ASP.NET Core: 5783 | 5784 | * DI Container which is quite simple and built-in. You can extend it with other popular DI containers 5785 | * Built-in and extensible structured logging. You can redirect output to as many sources as you want (file, Azure, AWS, console) 5786 | * Extensible strongly typed configuration, which can also be used to reload at run-time 5787 | * Kestrel – new, cross-platform and super fast web server which can stand alone without IIS, Nginx or Apache 5788 | * New, fully async pipeline. It is easily configured via middleware 5789 | * ASP.NET All meta package which improves development speed, and enables you to reference all Microsoft packages for ASP.NET Core and it will deploy only those that are being used by your code 5790 | * There is no _web.config_. We now use _appsettings.json_ file in combination with other sources of configuration (command line args, environment variables, etc.) 5791 | * There is no _Global._asax – We have _Startup.cs_ which is used to set up Middleware and services for DI Container. 5792 | 5793 | **Source:** _talkingdotnet.com_ 5794 | 5795 | #### Q4: Can ASP.NET Core work with the .NET framework? ⭐⭐ 5796 | **Answer:** 5797 | Yes. This might surprise many, but ASP.NET Core works with .NET framework and this is officially supported by Microsoft. 5798 | 5799 | ASP.NET Core works with: 5800 | 5801 | * .NET Core framework 5802 | * .NET framework 5803 | 5804 | **Source:** _talkingdotnet.com_ 5805 | 5806 | #### Q5: Explain startup process in ASP.NET Core? ⭐⭐ 5807 | **Answer:** 5808 | Everything starts from Program.cs 5809 | ```csharp 5810 | public static void Main(string[] args) 5811 | { 5812 | BuildWebHost(args).Run(); 5813 | } 5814 | 5815 | public static IWebHost BuildWebHost(string[] args) => 5816 | WebHost.CreateDefaultBuilder(args) 5817 | .UseStartup() 5818 | .Build(); 5819 | ``` 5820 | 5821 | CreateDefaultBuilder extension method will create a default configuration which will look first into `appsettings.json` files then will look for Environment variables and at the end, it will use command line arguments. 5822 | 5823 | This part will also set up default logger sources (debug and console) and load the settings for logging from appsettings.json. 5824 | 5825 | After the `CreateDefaultBuilder` finishes, then `Startup` class is executed. First, the constructor code is executed. After that, services are added to DI container via `AddServices` method that lives in Startup class. After that, an order of middleware that will handle every incoming request is set up. 5826 | 5827 | **Source:** _codingblast.com_ 5828 | 5829 | #### Q6: What is the difference between ASP.NET and ASP.NET MVC? ⭐⭐ 5830 | **Answer:** 5831 | ASP.NET, at its most basic level, provides a means for you to provide general HTML markup combined with server side "controls" within the event-driven programming model that can be leveraged with VB, C#, and so on. You define the page(s) of a site, drop in the controls, and provide the programmatic plumbing to make it all work. 5832 | 5833 | ASP.NET MVC is an application framework based on the Model-View-Controller architectural pattern. This is what might be considered a "canned" framework for a specific way of implementing a web site, with a page acting as the "controller" and dispatching requests to the appropriate pages in the application. The idea is to "partition" the various elements of the application, eg business rules, presentation rules, and so on. 5834 | 5835 | Think of the former as the "blank slate" for implementing a site architecture you've designed more or less from the ground up. MVC provides a mechanism for designing a site around a pre-determined "pattern" of application access, if that makes sense. There's more technical detail to it than that, to be sure, but that's the nickel tour for the purposes of the question. 5836 | 5837 | **Source:** _stackoverflow.com_ 5838 | 5839 | #### Q7: What is a postback? ⭐⭐ 5840 | **Answer:** 5841 | A **postback** originates from the client browser. Usually one of the controls on the page will be manipulated by the user (a button clicked or dropdown changed, etc), and this control will initiate a postback. The state of this control, plus all other controls on the page (known as the View State) is Posted Back to the web server. 5842 | 5843 | **Source:** _stackoverflow.com_ 5844 | 5845 | #### Q8: What is ViewState? ⭐⭐ 5846 | **Answer:** 5847 | **View State** is the method to preserve the Value of the Page and Controls between round trips. It is a Page-Level State Management technique. View State is turned on by default and normally serializes the data in every control on the page regardless of whether it is actually used during a post-back. 5848 | 5849 | A web application is stateless. That means that a new instance of a page is created every time when we make a request to the server to get the page and after the round trip our page has been lost immediately 5850 | 5851 | **Source:** _c-sharpcorner.com_ 5852 | 5853 | #### Q9: What exactly is an application pool? What is its purpose? ⭐⭐ 5854 | **Answer:** 5855 | **Application pools** allow you to isolate your applications from one another, even if they are running on the same server. This way, if there is an error in one app, it won't take down other applications. 5856 | 5857 | Additionally, applications pools allow you to separate different apps which require different levels of security. 5858 | 5859 | **Source:** _stackoverflow.com_ 5860 | 5861 | #### Q10: Explain Middleware in ASP.NET Core? ⭐⭐⭐ 5862 | **Answer:** 5863 | Middleware is actually sequential series of delegates (piece of code), that can either short-circuit or pass on the HTTP request to next delegate. These are known as middleware, a concept well known to people who worked with Node.js. 5864 | 5865 | Piece of your middleware can do one of the following: 5866 | 5867 | * Handle an incoming HTTP request by generating an HTTP response (maybe your authentication or authorization middleware will stop the request early and immediately create response) 5868 | * Process the incoming request, change it and pass it to the next middleware in the pipeline 5869 | * Process the outgoing response, change it and pass it on to next middleware in the pipeline or directly to the ASP.NET Core web server 5870 | 5871 | **Source:** _talkingdotnet.com_ 5872 | 5873 | #### Q11: What are the different types of caching? ⭐⭐⭐ 5874 | **Answer:** 5875 | ASP.NET has 3 kinds of caching : 5876 | 5877 | 1. Output Caching, 5878 | 2. Fragment Caching, 5879 | 3. Data Caching. 5880 | 5881 | **Source:** _guru99.com_ 5882 | 5883 | #### Q12: How long the items in ViewState exists? ⭐⭐⭐ 5884 | **Answer:** 5885 | They exist for the life of the current page. 5886 | 5887 | **Source:** _guru99.com_ 5888 | 5889 | #### Q13: In which event of page cycle is the ViewState available? ⭐⭐⭐ 5890 | **Answer:** 5891 | After the Init() and before the Page_Load(). 5892 | 5893 | **Source:** _guru99.com_ 5894 | 5895 | #### Q14: What are the sub types of ActionResult? ⭐⭐⭐ 5896 | **Answer:** 5897 | ActionResult is used to represent the action method result. Below are the subtypes of ActionResult: 5898 | 5899 | * ViewResult 5900 | * PartialViewResult 5901 | * RedirectToRouteResult 5902 | * RedirectResult 5903 | * JavascriptResult 5904 | * JSONResult 5905 | * FileResult 5906 | * HTTPStatusCodeResult 5907 | 5908 | **Source:** _medium.com_ 5909 | 5910 | #### Q15: What is the difference between Server.Transfer and Response.Redirect? ⭐⭐⭐ 5911 | **Answer:** 5912 | In Server.Transfer page processing transfers from one page to the other page without making a round-trip back to the client's browser. This provides a faster response with a little less overhead on the server. The clients url history list or current url Server does not update in case of Server.Transfer. 5913 | 5914 | Response.Redirect is used to redirect the user's browser to another page or site. It performs trip back to the client where the client's browser is redirected to the new page. The user's browser history list is updated to reflect the new address. 5915 | 5916 | **Source:** _guru99.com_ 5917 | 5918 | #### Q16: How can we prevent browser from caching an ASPX page? ⭐⭐⭐ 5919 | **Answer:** 5920 | We can SetNoStore on HttpCachePolicy object exposed by the Response object's Cache property: 5921 | 5922 | ```csharp 5923 | Response.Cache.SetNoStore(); 5924 | Response.Write(DateTime.Now.ToLongTimeString ()); 5925 | ``` 5926 | 5927 | **Source:** _guru99.com_ 5928 | 5929 | #### Q17: What are the event handlers that we can have in Global.asax file? ⭐⭐⭐ 5930 | **Answer:** 5931 | * **Application Events:** Application_Start , Application_End, Application_AcquireRequestState, Application_AuthenticateRequest, Application_AuthorizeRequest, Application_BeginRequest, Application_Disposed, Application_EndRequest, Application_Error, Application_PostRequestHandlerExecute, Application_PreRequestHandlerExecute,Application_PreSendRequestContent, Application_PreSendRequestHeaders, Application_ReleaseRequestState, Application_ResolveRequestCache, Application_UpdateRequestCache 5932 | 5933 | * **Session Events:** Session_Start,Session_End 5934 | 5935 | **Source:** _guru99.com_ 5936 | 5937 | #### Q18: In which event are the controls fully loaded? ⭐⭐⭐ 5938 | **Answer:** 5939 | **Page load** event. 5940 | 5941 | **Source:** _guru99.com_ 5942 | 5943 | #### Q19: What is ViewState? How is it encoded? Is it encrypted? Who uses ViewState? ⭐⭐⭐ 5944 | **Answer:** 5945 | **View state** is a kind of hash map (or at least you can think of it that way) that ASP.NET uses to store all the temporary information about a page - like what options are currently chosen in each select box, what values are there in each text box, which panel are open, etc. You can also use it to store any arbitrary information. 5946 | 5947 | The entire map is serialized and encoded and kept in a _hidden variable_ (__VIEWSTATE form field) that's posted back to the server whenever you take any action on the page that requires a server round trip. This is how you can access the values on the controls from the server code. If you change any value in the server code, that change is made in the view state and sent back to the browser. 5948 | 5949 | Just be careful about how much information you store in the view state, though... it can quickly become bloated and slow to transfer each time to the server and back. 5950 | 5951 | It's not encrypted at all. Just base encoded, which easily reversible. 5952 | 5953 | **Source:** _stackoverflow.com_ 5954 | 5955 | #### Q20: What exactly is the difference between .NET Core and ASP.NET Core? ⭐⭐⭐ 5956 | **Answer:** 5957 | **.NET Core** is a runtime. It can execute applications that are built for it. 5958 | 5959 | **ASP.NET Core** is a collection of libraries that form a Framework for building web applications. ASP.NET Core libraries can be used on both .NET Core and the "Full .NET Framework" (what has shipped with windows for many years). 5960 | 5961 | **Source:** _stackoverflow.com_ 5962 | 5963 | #### Q21: What are the different Session state management options available in ASP.NET? ⭐⭐⭐⭐ 5964 | **Answer:** 5965 | Read Full Answer on 👉 FullStack.Cafe 5966 | 5967 | #### Q22: What is the difference between web config and machine config? ⭐⭐⭐⭐ 5968 | **Answer:** 5969 | Read Full Answer on 👉 FullStack.Cafe 5970 | 5971 | #### Q23: List the major built-in objects in ASP.NET? ⭐⭐⭐⭐ 5972 | **Answer:** 5973 | Read Full Answer on 👉 FullStack.Cafe 5974 | 5975 | #### Q24: What are the different types of cookies in ASP.NET? ⭐⭐⭐⭐ 5976 | **Answer:** 5977 | Read Full Answer on 👉 FullStack.Cafe 5978 | 5979 | #### Q25: What is Katana? ⭐⭐⭐⭐ 5980 | **Answer:** 5981 | Read Full Answer on 👉 FullStack.Cafe 5982 | 5983 | #### Q26: How to choose between ASP.NET 4.x and ASP.NET Core? ⭐⭐⭐⭐ 5984 | **Answer:** 5985 | Read Full Answer on 👉 FullStack.Cafe 5986 | 5987 | #### Q27: What is an HttpHandler in ASP.NET? Why and how is it used? ⭐⭐⭐⭐ 5988 | **Answer:** 5989 | Read Full Answer on 👉 FullStack.Cafe 5990 | 5991 | #### Q28: What is the difference between and ? ⭐⭐⭐⭐ 5992 | **Answer:** 5993 | Read Full Answer on 👉 FullStack.Cafe 5994 | 5995 | #### Q29: What is HttpModule in ASP.Net? ⭐⭐⭐⭐ 5996 | **Answer:** 5997 | Read Full Answer on 👉 FullStack.Cafe 5998 | 5999 | #### Q30: Name some ASP.NET WebForms disadvantages over MVC? ⭐⭐⭐⭐⭐ 6000 | **Answer:** 6001 | Read Full Answer on 👉 FullStack.Cafe 6002 | 6003 | #### Q31: What exactly is OWIN and what problems does it solve? ⭐⭐⭐⭐⭐ 6004 | **Answer:** 6005 | Read Full Answer on 👉 FullStack.Cafe 6006 | 6007 | #### Q32: Are static class instances unique to a request or a server in ASP.NET? ⭐⭐⭐⭐⭐ 6008 | **Details:** 6009 | On an ASP.NET website, are static classes unique to each web request, or are they instantiated whenever needed and GCed whenever the GC decides to disposed of them? 6010 | 6011 | **Answer:** 6012 | Read Full Answer on 👉 FullStack.Cafe 6013 | 6014 | #### Q33: What are the Advantages of Using ASP.NET Web API? ⭐⭐ 6015 | **Answer:** 6016 | Using ASP.NET Web API has a number of advantages, but core of the advantages are: 6017 | 6018 | * It works the HTTP way using standard HTTP verbs like `GET`, `POST`, `PUT`, `DELETE`, etc. for all CRUD operations 6019 | * Complete support for routing 6020 | * Response generated in JSON or XML format using `MediaTypeFormatter` 6021 | * It has the ability to be hosted in IIS as well as self-host outside of IIS 6022 | * Supports Model binding and Validation 6023 | * Support for OData 6024 | 6025 | **Source:** _codeproject.com_ 6026 | 6027 | #### Q34: Compare WCF vs ASP.NET Web API? ⭐⭐⭐ 6028 | **Answer:** 6029 | * **Windows Communication Foundation** is designed to exchange standard SOAP-based messages using variety of transport protocols like HTTP, TCP, NamedPipes or MSMQ, etc. 6030 | * On the other hand, **ASP.NET API** is a framework for building non-SOAP based services over HTTP only. 6031 | 6032 | **Source:** _codeproject.com_ 6033 | 6034 | #### Q35: What's the difference between REST & RESTful? ⭐⭐⭐ 6035 | **Answer:** 6036 | * Representational state transfer (REST) is a style of software architecture. As described in a dissertation by Roy Fielding, REST is an "architectural style" that basically exploits the existing technology and protocols of the Web. 6037 | * RESTful is typically used to refer to web services implementing such an architecture. 6038 | 6039 | **Source:** _stackoverflow.com_ 6040 | 6041 | #### Q36: What's the difference between OpenID and OAuth? ⭐⭐⭐⭐ 6042 | **Answer:** 6043 | Read Full Answer on 👉 FullStack.Cafe 6044 | 6045 | #### Q37: Explain the difference between WCF, Web API, WCF REST and Web Service? ⭐⭐⭐⭐⭐ 6046 | **Answer:** 6047 | Read Full Answer on 👉 FullStack.Cafe 6048 | 6049 | ## [[⬆]](#toc) 39 Advanced React Interview Questions You Must Clarify (2020 Update) 6050 | > Originally published on 👉 39 Advanced React Interview Questions You Must Clarify (2020 Update) | FullStack.Cafe 6051 | 6052 | #### Q1: What is virtual DOM? ⭐ 6053 | **Answer:** 6054 | **The virtual DOM (VDOM)** is an in-memory representation of Real DOM. The representation of a UI is kept in memory and synced with the “real” DOM. It’s a step that happens between the render function being called and the displaying of elements on the screen. This entire process is called reconciliation. 6055 | 6056 | **Source:** _github.com/sudheerj_ 6057 | 6058 | #### Q2: What are the differences between a class component and functional component? ⭐⭐ 6059 | **Answer:** 6060 | - **Class components** allows you to use additional features such as local state and lifecycle hooks. Also, to enable your component to have direct access to your store and thus holds state. 6061 | 6062 | - When your component just receives props and renders them to the page, this is a **stateless component**, for which a pure function can be used. These are also called dumb components or presentational components. 6063 | 6064 | **Source:** _github.com/Pau1fitz_ 6065 | 6066 | #### Q3: What are refs used for in React? ⭐⭐ 6067 | **Answer:** 6068 | *Refs* are an escape hatch which allow you to get direct access to a DOM element or an instance of a component. In order to use them you add a ref attribute to your component whose value is a callback function which will receive the underlying DOM element or the mounted instance of the component as its first argument. 6069 | 6070 | ```js 6071 | class UnControlledForm extends Component { 6072 | handleSubmit = () => { 6073 | console.log("Input Value: ", this.input.value) 6074 | } 6075 | render () { 6076 | return ( 6077 | 6083 | ) 6084 | } 6085 | } 6086 | ``` 6087 | Above notice that our input field has a ref attribute whose value is a function. That function receives the actual DOM element of input which we then put on the instance in order to have access to it inside of the handleSubmit function. 6088 | 6089 | It’s often misconstrued that you need to use a class component in order to use refs, but refs can also be used with functional components by leveraging closures in JavaScript. 6090 | 6091 | ```js 6092 | function CustomForm ({handleSubmit}) { 6093 | let inputElement 6094 | return ( 6095 | 6101 | ) 6102 | } 6103 | ``` 6104 | 6105 | **Source:** _github.com/Pau1fitz_ 6106 | 6107 | #### Q4: Describe how events are handled in React. ⭐⭐ 6108 | **Answer:** 6109 | In order to solve cross browser compatibility issues, your event handlers in React will be passed instances of SyntheticEvent, which is React’s cross-browser wrapper around the browser’s native event. These synthetic events have the same interface as native events you’re used to, except they work identically across all browsers. 6110 | 6111 | What’s mildly interesting is that React doesn’t actually attach events to the child nodes themselves. React will listen to all events at the top level using a single event listener. This is good for performance and it also means that React doesn’t need to worry about keeping track of event listeners when updating the DOM. 6112 | 6113 | **Source:** _tylermcginnis.com_ 6114 | 6115 | #### Q5: What is the difference between state and props? ⭐⭐ 6116 | **Answer:** 6117 | Both **props** and **state** are plain JavaScript objects. While both of them hold information that influences the output of render, they are different in their functionality with respect to component. i.e, 6118 | * Props get passed to the component similar to function parameters 6119 | * state is managed within the component similar to variables declared within a function. 6120 | 6121 | **Source:** _https://github.com/sudheerj_ 6122 | 6123 | #### Q6: How to create refs? ⭐⭐ 6124 | **Answer:** 6125 | **Refs** are created using `React.createRef()` method and attached to React elements via the ref attribute. In order to use refs throughout the component, just assign the ref to the instance property with in constructor. 6126 | ```js 6127 | class MyComponent extends React.Component { 6128 | constructor(props) { 6129 | super(props); 6130 | this.myRef = React.createRef(); 6131 | } 6132 | render() { 6133 | return

; 6134 | } 6135 | } 6136 | ``` 6137 | And: 6138 | ```js 6139 | class UserForm extends Component { 6140 | handleSubmit = () => { 6141 | console.log("Input Value is: ", this.input.value) 6142 | } 6143 | render () { 6144 | return ( 6145 | 6151 | ) 6152 | } 6153 | } 6154 | ``` 6155 | We can also use it in functional components with the help of closures. 6156 | 6157 | **Source:** _github.com/sudheerj_ 6158 | 6159 | #### Q7: What are Higher-Order components? ⭐⭐ 6160 | **Answer:** 6161 | A higher-order component **(HOC)** is a function that takes a component and returns a new component. Basically, it’s a pattern that is derived from React’s compositional nature 6162 | We call them as **“pure’ components”** because they can accept any dynamically provided child component but they won’t modify or copy any behavior from their input components. 6163 | ```js 6164 | const EnhancedComponent = higherOrderComponent(WrappedComponent); 6165 | ``` 6166 | HOC can be used for many use cases as below, 6167 | 6168 | 1. Code reuse, logic and bootstrap abstraction 6169 | 2. Render High jacking 6170 | 3. State abstraction and manipulation 6171 | 4. Props manipulation 6172 | 6173 | **Source:** _github.com/sudheerj_ 6174 | 6175 | #### Q8: What is the purpose of using super constructor with props argument? ⭐⭐ 6176 | **Answer:** 6177 | A child class constructor cannot make use of **this** reference until `super()` method has been called. The same applies for ES6 sub-classes as well. The main reason of passing props parameter to super() call is to access this.props in your child constructors. 6178 | 6179 | **Passing props:** 6180 | ```js 6181 | class MyComponent extends React.Component { 6182 | constructor(props) { 6183 | super(props); 6184 | console.log(this.props); // Prints { name: 'sudheer',age: 30 } 6185 | } 6186 | } 6187 | ``` 6188 | **Not passing props:** 6189 | ```js 6190 | class MyComponent extends React.Component { 6191 | constructor(props) { 6192 | super(); 6193 | console.log(this.props); // Prints undefined 6194 | // But Props parameter is still available 6195 | console.log(props); // Prints { name: 'sudheer',age: 30 } 6196 | } 6197 | 6198 | render() { 6199 | // No difference outside constructor 6200 | console.log(this.props) // Prints { name: 'sudheer',age: 30 } 6201 | } 6202 | } 6203 | ``` 6204 | 6205 | The above code snippets reveals that this.props behavior is different only with in the constructor. It would be same outside the constructor. 6206 | 6207 | **Source:** _github.com/sudheerj_ 6208 | 6209 | #### Q9: What are controlled components? ⭐⭐⭐ 6210 | **Answer:** 6211 | In HTML, form elements such as ``, `

`, and `<select>` typically maintain their own state and update it based on user input. When a user submits a form the values from the aforementioned elements are sent with the form. With React it works differently. The component containing the form will keep track of the value of the input in it's state and will re-render the component each time the callback function e.g. `onChange` is fired as the state will be updated. An input form element whose value is controlled by React in this way is called a **controlled component**.
 6212 | 
 6213 | **Source:** _github.com/Pau1fitz_
 6214 | 
 6215 | #### Q10: What is equivalent of the following using React.createElement? ⭐⭐⭐
 6216 | **Answer:**
 6217 | **Question**:
 6218 | 
 6219 | ```js
 6220 | const element = (
 6221 |   <h1 className="greeting">
 6222 |     Hello, world!
 6223 |   </h1>
 6224 | );
 6225 | ```
 6226 | What is equivalent of the following using `React.createElement`?
 6227 | 
 6228 | **Answer**:
 6229 | 
 6230 | ```js
 6231 | const element = React.createElement(
 6232 |   'h1',
 6233 |   {className: 'greeting'},
 6234 |   'Hello, world!'
 6235 | );
 6236 | ```
 6237 | 
 6238 | **Source:** _github.com/Pau1fitz_
 6239 | 
 6240 | #### Q11: What can you tell me about JSX? ⭐⭐⭐
 6241 | **Answer:**
 6242 | When Facebook first released React to the world, they also introduced a new dialect of JavaScript called JSX that embeds raw HTML templates inside JavaScript code. JSX code by itself cannot be read by the browser; it must be transpiled into traditional JavaScript using tools like Babel and webpack. While many developers understandably have initial knee-jerk reactions against it, JSX (in tandem with ES2015) has become the defacto method of defining React components.
 6243 | 
 6244 | ```js
 6245 | class MyComponent extends React.Component {
 6246 |   render() {
 6247 |     let props = this.props;  
 6248 |     return (
 6249 |       <div className="my-component">
 6250 |       <a href={props.url}>{props.name}</a>
 6251 |       </div>
 6252 |     );
 6253 |   }
 6254 | }
 6255 | ```
 6256 | 
 6257 | **Source:** _codementor.io_
 6258 | 
 6259 | #### Q12: Given the code defined above, can you identify two problems? ⭐⭐⭐
 6260 | **Answer:**
 6261 | Take a look at the code below:
 6262 | 
 6263 | ```js
 6264 | class MyComponent extends React.Component {
 6265 |   constructor(props) {
 6266 |     // set the default internal state
 6267 |     this.state = {
 6268 |       clicks: 0
 6269 |     };
 6270 |   }
 6271 | 
 6272 |   componentDidMount() {
 6273 |     this.refs.myComponentDiv.addEventListener('click', this.clickHandler);
 6274 |   }
 6275 | 
 6276 |   componentWillUnmount() {
 6277 |     this.refs.myComponentDiv.removeEventListener('click', this.clickHandler);
 6278 |   }
 6279 | 
 6280 |   clickHandler() {
 6281 |     this.setState({
 6282 |       clicks: this.clicks + 1
 6283 |     });
 6284 |   }
 6285 | 
 6286 |   render() {
 6287 |     let children = this.props.children;
 6288 | 
 6289 |     return (
 6290 |       <div className="my-component" ref="myComponentDiv">
 6291 |       <h2>My Component ({this.state.clicks} clicks})</h2>
 6292 |       <h3>{this.props.headerText}</h3>
 6293 |     {children}
 6294 |     </div>
 6295 |     );
 6296 |   }
 6297 | }
 6298 | 
 6299 | ```
 6300 | Given the code defined above, can you identify two problems?
 6301 | 
 6302 | **Answer:**
 6303 | 1.  The constructor does not pass its props to the super class. It should include the following line:
 6304 | 
 6305 | ```js
 6306 | constructor(props) {
 6307 |   super(props);
 6308 |   // ...
 6309 | }
 6310 |   ```  
 6311 | 
 6312 | 2.  The event listener (when assigned via `addEventListener()`) is not properly scoped because [ES2015 doesn’t provide autobinding](https://facebook.github.io/react/docs/reusable-components.html#no-autobinding). Therefore the developer can re-assign `clickHandler` in the constructor to include the correct binding to this:
 6313 | 
 6314 | ```js
 6315 | constructor(props) {
 6316 |   super(props);
 6317 |   this.clickHandler = this.clickHandler.bind(this);
 6318 |   // ...
 6319 | }
 6320 | ```
 6321 | 
 6322 | **Source:** _codementor.io_
 6323 | 
 6324 | #### Q13: Why should not we update the state directly? ⭐⭐⭐
 6325 | **Answer:**
 6326 | If you try to update state directly then it won’t re-render the component.
 6327 | 
 6328 | ```js
 6329 |     //Wrong
 6330 |     This.state.message =”Hello world”;
 6331 | ```
 6332 | 
 6333 | Instead use `setState()` method. It schedules an update to a component’s state object. When state changes, the component responds by re-rendering
 6334 | 
 6335 | ```js
 6336 |     //Correct
 6337 |     This.setState({message: ‘Hello World’});
 6338 | ```
 6339 | 
 6340 | **Note:** The only place you can assign the state is constructor.
 6341 | 
 6342 | 
 6343 | **Source:** _https://github.com/sudheerj_
 6344 | 
 6345 | #### Q14: What are the different phases of ReactJS component lifecycle? ⭐⭐⭐
 6346 | **Answer:**
 6347 | There are four different phases of React component’s lifecycle:
 6348 | 1. **Initialization:** In this phase react component prepares setting up the initial state and default props.
 6349 | 2. **Mounting:** The react component is ready to mount in the browser DOM. This phase covers **componentWillMount** and **componentDidMount** lifecycle methods.
 6350 | 3. **Updating:** In this phase, the component get updated in two ways, sending the new props and updating the state. This phase covers **shouldComponentUpdate, componentWillUpdate and componentDidUpdate** lifecycle methods.
 6351 | 4. **Unmounting:** In this last phase, the component is not needed and get unmounted from the browser DOM. This phase include **componentWillUnmount** lifecycle method.
 6352 | 
 6353 | <div class="text-center">
 6354 | <img src="https://github.com/sudheerj/reactjs-interview-questions/raw/master/images/phases.png" class="img-fluid"/>
 6355 | </div>
 6356 | 
 6357 | **Source:** _github.com/sudheerj_
 6358 | 
 6359 | #### Q15: What are the lifecycle methods of ReactJS? ⭐⭐⭐
 6360 | **Answer:**
 6361 | -	**componentWillMount:** Executed before rendering and is used for App level configuration in your root component.
 6362 | -	**componentDidMount:** Executed after first rendering and here all AJAX requests, DOM or state updates, and set up eventListeners should occur.
 6363 | -	**componentWillReceiveProps:** Executed when particular prop updates to trigger state transitions.
 6364 | -	**shouldComponentUpdate:** Determines if the component will be updated or not. By default it returns true. If you are sure that the component doesn't need to render after state or props are updated, you can return false value. It is a great place to improve performance as it allows you to prevent a rerender if component receives new prop.
 6365 | -	**componentWillUpdate:** Executed before re-rendering the component when there are pros & state changes confirmed by shouldComponentUpdate  which returns true.
 6366 | -	**componentDidUpdate:** Mostly it is used to update the DOM in response to prop or state changes.
 6367 | -   **componentWillUnmount:** It will be used to cancel any outgoing network requests, or remove all event listeners associated with the component.
 6368 | 
 6369 | 
 6370 | **Source:** _github.com/sudheerj_
 6371 | 
 6372 | #### Q16: What do these three dots (...) in React do? ⭐⭐⭐
 6373 | **Details:**
 6374 | What does the ... do in this React (using JSX) code and what is it called?
 6375 | 
 6376 | ```html
 6377 | <Modal {...this.props} title='Modal heading' animation={fal
 6378 | ```
 6379 | 
 6380 | **Answer:**
 6381 | That's property spread notation. It was added in ES2018 (spread for arrays/iterables was earlier, ES2015).
 6382 | 
 6383 | For instance, if this.props contained a: 1 and b: 2, then
 6384 | ```html
 6385 | <Modal {...this.props} title='Modal heading' animation={false}>
 6386 | ```
 6387 | would be the same as:
 6388 | ```html
 6389 | <Modal a={this.props.a} b={this.props.b} title='Modal heading' animation={false}>
 6390 | ```
 6391 | 
 6392 | Spread notation is handy not only for that use case, but for creating a new object with most (or all) of the properties of an existing object — which comes up a lot when you're updating state, since you can't modify state directly:
 6393 | 
 6394 | ```js
 6395 | this.setState(prevState => {
 6396 |     return {foo: {...prevState.foo, a: "updated"}};
 6397 | });
 6398 | ```
 6399 | 
 6400 | **Source:** _stackoverflow.com_
 6401 | 
 6402 | #### Q17: What are advantages of using React Hooks? ⭐⭐⭐
 6403 | **Answer:**
 6404 | Primarily, hooks in general enable the extraction and reuse of stateful logic that is common across multiple components without the burden of higher order components or render props. Hooks allow to easily manipulate the state of our functional component without needing to convert them into class components.
 6405 | 
 6406 | Hooks don’t work inside classes (because they let you use React without classes). By using them, we can totally avoid using lifecycle methods, such as `componentDidMount`, `componentDidUpdate`, `componentWillUnmount`. Instead, we will use built-in hooks like `useEffect` .
 6407 | 
 6408 | **Source:** _hackernoon.com_
 6409 | 
 6410 | #### Q18: What are React Hooks? ⭐⭐⭐
 6411 | **Answer:**
 6412 | **Hooks** are a new addition in React 16.8. They let you use state and other React features without writing a class. With Hooks, you can extract stateful logic from a component so it can be tested independently and reused. Hooks allow you to reuse stateful logic without changing your component hierarchy. This makes it easy to share Hooks among many components or with the community.
 6413 | 
 6414 | **Source:** _reactjs.org_
 6415 | 
 6416 | #### Q19: What is useState() in React? ⭐⭐⭐
 6417 | **Details:**
 6418 | Explain what is the use of `useState(0)` there:
 6419 | ```js
 6420 | ...
 6421 | const [count, setCounter] = useState(0);
 6422 | const [moreStuff, setMoreStuff] = useState(...);
 6423 | ...
 6424 | 
 6425 | const setCount = () => {
 6426 |     setCounter(count + 1);
 6427 |     setMoreStuff(...);
 6428 |     ...
 6429 | };
 6430 | ```
 6431 | 
 6432 | **Answer:**
 6433 | `useState` is one of build-in react hooks. `useState(0)` returns a tuple where the first parameter count is the current state of the counter and setCounter is the method that will allow us to update the counter's state. 
 6434 | 
 6435 | We can use the `setCounter` method to update the state of count anywhere - In this case we are using it inside of the setCount function where we can do more things; the idea with hooks is that we are able to keep our code more functional and avoid class based components if not desired/needed.
 6436 | 
 6437 | **Source:** _stackoverflow.com_
 6438 | 
 6439 | #### Q20: What is StrictMode in React? ⭐⭐⭐
 6440 | **Answer:**
 6441 | React's StrictMode is sort of a helper component that will help you write better react components, you can wrap a set of components with `<StrictMode />` and it'll basically:
 6442 | 
 6443 | * Verify that the components inside are following some of the recommended practices and warn you if not in the console.
 6444 | * Verify the deprecated methods are not being used, and if they're used strict mode will warn you in the console.
 6445 | * Help you prevent some side effects by identifying potential risks.
 6446 | 
 6447 | **Source:** _stackoverflow.com_
 6448 | 
 6449 | #### Q21: Why do class methods need to be bound to a class instance? ⭐⭐⭐
 6450 | **Answer:**
 6451 | In JavaScript, the value of `this` changes depending on the current context. Within React class component methods, developers normally expect this to refer to the current instance of a component, so it is necessary to _bind_ these methods to the instance. Normally this is done in the constructor—for example:
 6452 | 
 6453 | ```js
 6454 | class SubmitButton extends React.Component {
 6455 |   constructor(props) {
 6456 |     super(props);
 6457 |     this.state = {
 6458 |       isFormSubmitted: false
 6459 |     };
 6460 |     this.handleSubmit = this.handleSubmit.bind(this);
 6461 |   }
 6462 | 
 6463 |   handleSubmit() {
 6464 |     this.setState({
 6465 |       isFormSubmitted: true
 6466 |     });
 6467 |   }
 6468 | 
 6469 |   render() {
 6470 |     return (
 6471 |       <button onClick={this.handleSubmit}>Submit</button>
 6472 |     )
 6473 |   }
 6474 | }
 6475 | ```
 6476 | 
 6477 | **Source:** _toptal.com_
 6478 | 
 6479 | #### Q22: What is prop drilling and how can you avoid it? ⭐⭐⭐
 6480 | **Answer:**
 6481 | When building a React application, there is often the need for a deeply nested component to use data provided by another component that is much higher in the hierarchy. The simplest approach is to simply pass a prop from each component to the next in the hierarchy from the source component to the deeply nested component. This is called **prop drilling**.
 6482 | 
 6483 | The primary disadvantage of prop drilling is that components that should not otherwise be aware of the data become unnecessarily complicated and are harder to maintain.
 6484 | 
 6485 | To avoid prop drilling, a common approach is to use React context. This allows a `Provider` component that supplies data to be defined, and allows nested components to consume context data via either a `Consumer` component or a `useContext` hook.
 6486 | 
 6487 | **Source:** _toptal.com_
 6488 | 
 6489 | #### Q23: Describe Flux vs MVC? ⭐⭐⭐⭐
 6490 | **Answer:**
 6491 | Read Full Answer on 👉 <a href='https://www.fullstack.cafe\blog\react-js-interview-questions'>FullStack.Cafe</a>
 6492 | 
 6493 | #### Q24: What is the difference between a controlled component and an uncontrolled component? ⭐⭐⭐⭐
 6494 | **Answer:**
 6495 | Read Full Answer on 👉 <a href='https://www.fullstack.cafe\blog\react-js-interview-questions'>FullStack.Cafe</a>
 6496 | 
 6497 | #### Q25: What is wrong with this code? ⭐⭐⭐⭐
 6498 | **Answer:**
 6499 | Read Full Answer on 👉 <a href='https://www.fullstack.cafe\blog\react-js-interview-questions'>FullStack.Cafe</a>
 6500 | 
 6501 | #### Q26: What is the React context? ⭐⭐⭐⭐
 6502 | **Answer:**
 6503 | Read Full Answer on 👉 <a href='https://www.fullstack.cafe\blog\react-js-interview-questions'>FullStack.Cafe</a>
 6504 | 
 6505 | #### Q27: What is React Fiber? ⭐⭐⭐⭐
 6506 | **Answer:**
 6507 | Read Full Answer on 👉 <a href='https://www.fullstack.cafe\blog\react-js-interview-questions'>FullStack.Cafe</a>
 6508 | 
 6509 | #### Q28: How to apply validation on Props in ReactJS? ⭐⭐⭐⭐
 6510 | **Answer:**
 6511 | Read Full Answer on 👉 <a href='https://www.fullstack.cafe\blog\react-js-interview-questions'>FullStack.Cafe</a>
 6512 | 
 6513 | #### Q29: What is the difference between ReactJS and Angular? ⭐⭐⭐⭐
 6514 | **Answer:**
 6515 | Read Full Answer on 👉 <a href='https://www.fullstack.cafe\blog\react-js-interview-questions'>FullStack.Cafe</a>
 6516 | 
 6517 | #### Q30: What is the difference between using constructor vs getInitialState in React? ⭐⭐⭐⭐
 6518 | **Answer:**
 6519 | Read Full Answer on 👉 <a href='https://www.fullstack.cafe\blog\react-js-interview-questions'>FullStack.Cafe</a>
 6520 | 
 6521 | #### Q31: When is it important to pass props to super(), and why? ⭐⭐⭐⭐
 6522 | **Answer:**
 6523 | Read Full Answer on 👉 <a href='https://www.fullstack.cafe\blog\react-js-interview-questions'>FullStack.Cafe</a>
 6524 | 
 6525 | #### Q32: How to conditionally add attributes to React components? ⭐⭐⭐⭐
 6526 | **Details:**
 6527 | Is there a way to only add attributes to a React component if a certain condition is met?
 6528 | 
 6529 | **Answer:**
 6530 | Read Full Answer on 👉 <a href='https://www.fullstack.cafe\blog\react-js-interview-questions'>FullStack.Cafe</a>
 6531 | 
 6532 | #### Q33: Do Hooks replace render props and higher-order components? ⭐⭐⭐⭐
 6533 | **Answer:**
 6534 | Read Full Answer on 👉 <a href='https://www.fullstack.cafe\blog\react-js-interview-questions'>FullStack.Cafe</a>
 6535 | 
 6536 | #### Q34: How would you go about investigating slow React application rendering? ⭐⭐⭐⭐
 6537 | **Answer:**
 6538 | Read Full Answer on 👉 <a href='https://www.fullstack.cafe\blog\react-js-interview-questions'>FullStack.Cafe</a>
 6539 | 
 6540 | #### Q35: When would you use StrictMode component in React? ⭐⭐⭐⭐
 6541 | **Answer:**
 6542 | Read Full Answer on 👉 <a href='https://www.fullstack.cafe\blog\react-js-interview-questions'>FullStack.Cafe</a>
 6543 | 
 6544 | #### Q36: What is a pure function? ⭐⭐⭐⭐⭐
 6545 | **Answer:**
 6546 | Read Full Answer on 👉 <a href='https://www.fullstack.cafe\blog\react-js-interview-questions'>FullStack.Cafe</a>
 6547 | 
 6548 | #### Q37: How does React renderer work exactly when we call setState?  ⭐⭐⭐⭐⭐
 6549 | **Answer:**
 6550 | Read Full Answer on 👉 <a href='https://www.fullstack.cafe\blog\react-js-interview-questions'>FullStack.Cafe</a>
 6551 | 
 6552 | #### Q38: What is the key architectural difference between a JavaScript library such as React and a JavaScript framework such as Angular? ⭐⭐⭐⭐⭐
 6553 | **Answer:**
 6554 | Read Full Answer on 👉 <a href='https://www.fullstack.cafe\blog\react-js-interview-questions'>FullStack.Cafe</a>
 6555 | 
 6556 | #### Q39: How to avoid the need for binding in React? ⭐⭐⭐⭐⭐
 6557 | **Answer:**
 6558 | Read Full Answer on 👉 <a href='https://www.fullstack.cafe\blog\react-js-interview-questions'>FullStack.Cafe</a>
 6559 | 
 6560 | ## [[⬆]](#toc) <a name=40AdvancedOOPInterviewQuestionsandAnswers[2019Update]>40 Advanced OOP Interview Questions and Answers [2019 Update]</a>
 6561 | > Originally published on 👉 <a href='https://www.fullstack.cafe\blog\csharp-object-oriented-programming-interview-questions'>40 Advanced OOP Interview Questions and Answers [2019 Update] | FullStack.Cafe</a>
 6562 | 
 6563 | #### Q1: What is inheritance? ⭐
 6564 | **Answer:**
 6565 | **Inheritance** allows us to define a class in terms of another class, which makes it easier to create and maintain an application. This also provides an opportunity to reuse the code functionality and speeds up implementation time.
 6566 | 
 6567 | When creating a class, instead of writing completely new data members and member functions, the programmer can designate that the new class should inherit the members of an existing class. This existing class is called the base class, and the new class is referred to as the derived class.
 6568 | 
 6569 | The idea of inheritance implements the IS-A relationship. For example, mammal IS A animal, dog IS-A mammal hence dog IS-A animal as well, and so on.
 6570 | 
 6571 | **Source:** _tutorialspoint.com_
 6572 | 
 6573 | #### Q2: What is object-oriented programming (OOP)? ⭐
 6574 | **Answer:**
 6575 | OOP is a technique to develop logical modules, such as classes that contain properties, methods, fields, and events. An object is created in the program to represent a class. Therefore, an object encapsulates all the features, such as data and behavior that are associated to a class. OOP allows developers to develop modular programs and assemble them as software. Objects are used to access data and behaviors of different software modules, such as classes, namespaces, and sharable assemblies. .NET Framework supports only OOP languages, such as Visual Basic .NET, Visual C#, and Visual C++.
 6576 | 
 6577 | **Source:** _indiabix.com_
 6578 | 
 6579 | #### Q3: What is encapsulation? ⭐⭐
 6580 | **Answer:**
 6581 | **Encapsulation** is defined _as the process of enclosing one or more items within a physical or logical package_. Encapsulation, in object oriented programming methodology, prevents access to implementation details.
 6582 | 
 6583 | **Source:** _tutorialspoint.com_
 6584 | 
 6585 | #### Q4: What is polymorphism? ⭐⭐
 6586 | **Answer:**
 6587 | The word polymorphism means having many forms. In object-oriented programming paradigm, polymorphism is often expressed as _one interface, multiple functions_.
 6588 | 
 6589 | 
 6590 | **Source:** _tutorialspoint.com_
 6591 | 
 6592 | #### Q5: What is the difference between procedural and object-oriented programming? ⭐⭐
 6593 | **Answer:**
 6594 | Procedural programming is based upon the modular approach in which the larger programs are broken into procedures. Each procedure is a set of instructions that are executed one after another. On the other hand, OOP is based upon objects. An object consists of various elements, such as methods and variables.  
 6595 |   
 6596 | Access modifiers are not used in procedural programming, which implies that the entire data can be accessed freely anywhere in the program. In OOP, you can specify the scope of a particular data by using access modifiers - _public_, _private_, _internal_, _protected_, and _protected_ internal.
 6597 | 
 6598 | **Source:** _indiabix.com_
 6599 | 
 6600 | #### Q6: Explain the concept of constructor? ⭐⭐
 6601 | **Answer:**
 6602 | **Constructor** is a special method of a class, which is called automatically when the instance of a class is created. It is created with the same name as the class and initializes all class members, whenever you access the class. The main features of a constructor are as follows:
 6603 | * Constructors do not have any return type.
 6604 | * Constructors can be overloaded.
 6605 | * It is not mandatory to declare a constructor; it is invoked automatically by .NET Framework.
 6606 | 
 6607 | **Source:** _indiabix.com_
 6608 | 
 6609 | #### Q7: Why is the virtual keyword used in code? ⭐⭐
 6610 | **Answer:**
 6611 | The `virtual` keyword is used while defining a class to specify that the methods and the properties of that class can be overridden in derived classes.
 6612 | 
 6613 | **Source:** _indiabix.com_
 6614 | 
 6615 | #### Q8: What is the difference between a class and a structure? ⭐⭐
 6616 | **Answer:**
 6617 | **Class**:
 6618 | * A class is a reference type.
 6619 | * While instantiating a class, CLR allocates memory for its instance in heap.
 6620 | * Classes support inheritance.
 6621 | * Variables of a class can be assigned as null.
 6622 | * Class can contain constructor/destructor.
 6623 | 
 6624 | **Structure**:
 6625 | * A structure is a value type.
 6626 | * In structure, memory is allocated on stack.
 6627 | * Structures do not support inheritance.
 6628 | * Structure members cannot have null values.
 6629 | * Structure does not require constructor/destructor and members can be initialiazed automatically.
 6630 | 
 6631 | **Source:** _indiabix.com_
 6632 | 
 6633 | #### Q9: What is the relationship between a class and an object? ⭐⭐
 6634 | **Answer:**
 6635 | A class acts as a blue-print that defines the properties, states, and behaviors that are common to a number of objects. An object is an instance of the class. For example, you have a class called _Vehicle_ and _Car_ is the object of that class. You can create any number of objects for the class named _Vehicle_, such as _Van_, _Truck_, and _Auto_.  
 6636 |       
 6637 | The _new_ operator is used to create an object of a class. When an object of a class is instantiated, the system allocates memory for every data member that is present in the class.
 6638 | 
 6639 | **Source:** _indiabix.com_
 6640 | 
 6641 | #### Q10: When should I use a struct instead of a class? ⭐⭐⭐
 6642 | **Answer:**
 6643 | Do not define a structure unless the type has all of the following characteristics:
 6644 |  
 6645 | * It logically represents a single value, similar to primitive types (integer, double, and so on).
 6646 | * It has an instance size smaller than 16 bytes.
 6647 | * It is immutable.
 6648 | * It will not have to be boxed frequently.
 6649 | 
 6650 | **Source:** _stackoverflow.com_
 6651 | 
 6652 | #### Q11: What is polymorphism, what is it for, and how is it used? ⭐⭐⭐
 6653 | **Answer:**
 6654 | Polymorphism describes a pattern in object oriented programming in which classes have different functionality while sharing a common interface.
 6655 | 
 6656 | The beauty of polymorphism is that the code working with the different classes does not need to know which class it is using since they’re all used the same way. A real world analogy for polymorphism is a button. Everyone knows how to use a button: you simply apply pressure to it. What a button “does,” however, depends on what it is connected to and the context in which it is used — but the result does not affect how it is used. If your boss tells you to press a button, you already have all the information needed to perform the task.
 6657 | 
 6658 | **Source:** _stackoverflow.com_
 6659 | 
 6660 | #### Q12: What do you mean by data encapsulation? ⭐⭐⭐
 6661 | **Answer:**
 6662 | **Data encapsulation** is a concept of binding data and code in single unit called object and hiding all the implementation details of a class from the user. It prevents unauthorized access of data and restricts the user to use the necessary data only.
 6663 | 
 6664 | **Source:** _indiabix.com_
 6665 | 
 6666 | #### Q13: What are abstract classes? What are the distinct characteristics of an abstract class? ⭐⭐⭐
 6667 | **Answer:**
 6668 | An abstract class is a class that cannot be instantiated and is always used as a base class.  
 6669 | The following are the characteristics of an abstract class:  
 6670 | 
 6671 | *   You cannot instantiate an abstract class directly. This implies that you cannot create an object of the abstract class; it must be inherited.
 6672 | *   You can have abstract as well as non-abstract members in an abstract class.
 6673 | *   You must declare at least one abstract method in the abstract class.
 6674 | *   An abstract class is always public.
 6675 | *   An abstract class is declared using the _abstract_ keyword.
 6676 |   
 6677 | The basic purpose of an abstract class is to provide a common definition of the base class that multiple derived classes can share.
 6678 | 
 6679 | **Source:** _indiabix.com_
 6680 | 
 6681 | #### Q14: What are similarities between a class and a structure? ⭐⭐⭐
 6682 | **Answer:**
 6683 | The following are some of the similarities between a class and a structure:  
 6684 |     
 6685 | *   Access specifiers, such as _public_, _private_, and _protected_, are identically used in structures and classes to restrict the access of their data and methods outside their body.
 6686 | *   The access level for class members and struct members, including nested classes and structs, is private by default. Private nested types are not accessible from outside the containing type.
 6687 | *   Both can have constructors, methods, properties, fields, constants, enumerations, events, and event handlers.
 6688 | *   Both structures and classes can implement interfaces to use multiple-inheritance in code.
 6689 | *   Both structures and classes can have constructors with parameter.
 6690 | *   Both structures and classes can have delegates and events.
 6691 |     
 6692 | 
 6693 | **Source:** _indiabix.com_
 6694 | 
 6695 | #### Q15: How can you prevent a class from overriding in C#? ⭐⭐⭐
 6696 | **Answer:**
 6697 | You can prevent a class from overriding in C# by using the `sealed` keyword.
 6698 | 
 6699 | **Source:** _indiabix.com_
 6700 | 
 6701 | #### Q16: How is method overriding different from method overloading? ⭐⭐⭐
 6702 | **Answer:**
 6703 | * **Overriding** involves the creation of two or more methods with the same name and same signature in different classes (one of them should be parent class and other should be child). 
 6704 | * **Overloading** is a concept of using a method at different places with same name and different signatures within the same class.
 6705 | 
 6706 | **Source:** _indiabix.com_
 6707 | 
 6708 | #### Q17: Can you specify the accessibility modifier for methods inside the interface? ⭐⭐⭐
 6709 | **Answer:**
 6710 | All the methods inside an interface are always `public`, by default. You cannot specify any other access modifier for them.
 6711 | 
 6712 | **Source:** _indiabix.com_
 6713 | 
 6714 | #### Q18: Is it possible for a class to inherit the constructor of its base class? ⭐⭐⭐
 6715 | **Answer:**
 6716 | No, a class cannot inherit the constructor of its base class.
 6717 | 
 6718 | **Source:** _indiabix.com_
 6719 | 
 6720 | #### Q19: What is the difference between cohesion and coupling? ⭐⭐⭐⭐
 6721 | **Answer:**
 6722 | Read Full Answer on 👉 <a href='https://www.fullstack.cafe\blog\csharp-object-oriented-programming-interview-questions'>FullStack.Cafe</a>
 6723 | 
 6724 | #### Q20: What's the advantage of using getters and setters - that only get and set - instead of simply using public fields for those variables? ⭐⭐⭐⭐
 6725 | **Answer:**
 6726 | Read Full Answer on 👉 <a href='https://www.fullstack.cafe\blog\csharp-object-oriented-programming-interview-questions'>FullStack.Cafe</a>
 6727 | 
 6728 | #### Q21: What exactly is the difference between an interface and abstract class? ⭐⭐⭐⭐
 6729 | **Answer:**
 6730 | Read Full Answer on 👉 <a href='https://www.fullstack.cafe\blog\csharp-object-oriented-programming-interview-questions'>FullStack.Cafe</a>
 6731 | 
 6732 | #### Q22: What is Coupling in OOP? ⭐⭐⭐⭐
 6733 | **Answer:**
 6734 | Read Full Answer on 👉 <a href='https://www.fullstack.cafe\blog\csharp-object-oriented-programming-interview-questions'>FullStack.Cafe</a>
 6735 | 
 6736 | #### Q23: What is Cohesion in OOP? ⭐⭐⭐⭐
 6737 | **Answer:**
 6738 | Read Full Answer on 👉 <a href='https://www.fullstack.cafe\blog\csharp-object-oriented-programming-interview-questions'>FullStack.Cafe</a>
 6739 | 
 6740 | #### Q24: Explain the concept of destructor? ⭐⭐⭐⭐
 6741 | **Answer:**
 6742 | Read Full Answer on 👉 <a href='https://www.fullstack.cafe\blog\csharp-object-oriented-programming-interview-questions'>FullStack.Cafe</a>
 6743 | 
 6744 | #### Q25: Differentiate between an abstract class and an interface. ⭐⭐⭐⭐
 6745 | **Answer:**
 6746 | Read Full Answer on 👉 <a href='https://www.fullstack.cafe\blog\csharp-object-oriented-programming-interview-questions'>FullStack.Cafe</a>
 6747 | 
 6748 | #### Q26: What is a static constructor? ⭐⭐⭐⭐
 6749 | **Answer:**
 6750 | Read Full Answer on 👉 <a href='https://www.fullstack.cafe\blog\csharp-object-oriented-programming-interview-questions'>FullStack.Cafe</a>
 6751 | 
 6752 | #### Q27: Explain different types of inheritance. ⭐⭐⭐⭐
 6753 | **Answer:**
 6754 | Read Full Answer on 👉 <a href='https://www.fullstack.cafe\blog\csharp-object-oriented-programming-interview-questions'>FullStack.Cafe</a>
 6755 | 
 6756 | #### Q28: Does .NET support multiple inheritance? ⭐⭐⭐⭐
 6757 | **Answer:**
 6758 | Read Full Answer on 👉 <a href='https://www.fullstack.cafe\blog\csharp-object-oriented-programming-interview-questions'>FullStack.Cafe</a>
 6759 | 
 6760 | #### Q29: Can you declare an overridden method to be static if the original method is not static? ⭐⭐⭐⭐
 6761 | **Answer:**
 6762 | Read Full Answer on 👉 <a href='https://www.fullstack.cafe\blog\csharp-object-oriented-programming-interview-questions'>FullStack.Cafe</a>
 6763 | 
 6764 | #### Q30: Why Doesn't C# Allow Static Methods to Implement an Interface? ⭐⭐⭐⭐⭐
 6765 | **Answer:**
 6766 | Read Full Answer on 👉 <a href='https://www.fullstack.cafe\blog\csharp-object-oriented-programming-interview-questions'>FullStack.Cafe</a>
 6767 | 
 6768 | #### Q31: What is the difference between a mixin and inheritance? ⭐⭐⭐⭐⭐
 6769 | **Answer:**
 6770 | Read Full Answer on 👉 <a href='https://www.fullstack.cafe\blog\csharp-object-oriented-programming-interview-questions'>FullStack.Cafe</a>
 6771 | 
 6772 | #### Q32: In terms that an OOP programmer would understand (without any functional programming background), what is a monad? ⭐⭐⭐⭐⭐
 6773 | **Answer:**
 6774 | Read Full Answer on 👉 <a href='https://www.fullstack.cafe\blog\csharp-object-oriented-programming-interview-questions'>FullStack.Cafe</a>
 6775 | 
 6776 | #### Q33: What is LSP (Liskov Substitution Principle) and what are some examples of its use (good and bad)? ⭐⭐⭐⭐⭐
 6777 | **Answer:**
 6778 | Read Full Answer on 👉 <a href='https://www.fullstack.cafe\blog\csharp-object-oriented-programming-interview-questions'>FullStack.Cafe</a>
 6779 | 
 6780 | #### Q34: Could you elaborate Polymorphism vs Overriding vs Overloading? ⭐⭐⭐⭐⭐
 6781 | **Answer:**
 6782 | Read Full Answer on 👉 <a href='https://www.fullstack.cafe\blog\csharp-object-oriented-programming-interview-questions'>FullStack.Cafe</a>
 6783 | 
 6784 | #### Q35: What does it mean to “program to an interface”? ⭐⭐⭐⭐⭐
 6785 | **Answer:**
 6786 | Read Full Answer on 👉 <a href='https://www.fullstack.cafe\blog\csharp-object-oriented-programming-interview-questions'>FullStack.Cafe</a>
 6787 | 
 6788 | #### Q36: Can you provide a simple explanation of methods vs. functions in OOP context? ⭐⭐⭐⭐⭐
 6789 | **Answer:**
 6790 | Read Full Answer on 👉 <a href='https://www.fullstack.cafe\blog\csharp-object-oriented-programming-interview-questions'>FullStack.Cafe</a>
 6791 | 
 6792 | #### Q37: Why prefer composition over inheritance? What trade-offs are there for each approach? When should you choose inheritance over composition? ⭐⭐⭐⭐⭐
 6793 | **Answer:**
 6794 | Read Full Answer on 👉 <a href='https://www.fullstack.cafe\blog\csharp-object-oriented-programming-interview-questions'>FullStack.Cafe</a>
 6795 | 
 6796 | #### Q38: What is the difference between association, aggregation and composition? ⭐⭐⭐⭐⭐
 6797 | **Answer:**
 6798 | Read Full Answer on 👉 <a href='https://www.fullstack.cafe\blog\csharp-object-oriented-programming-interview-questions'>FullStack.Cafe</a>
 6799 | 
 6800 | #### Q39: Can you declare a private class in a namespace? ⭐⭐⭐⭐⭐
 6801 | **Answer:**
 6802 | Read Full Answer on 👉 <a href='https://www.fullstack.cafe\blog\csharp-object-oriented-programming-interview-questions'>FullStack.Cafe</a>
 6803 | 
 6804 | #### Q40: You have defined a destructor in a class that you have developed by using the C# programming language, but the destructor never executed. Why did the destructor not execute? ⭐⭐⭐⭐⭐
 6805 | **Answer:**
 6806 | Read Full Answer on 👉 <a href='https://www.fullstack.cafe\blog\csharp-object-oriented-programming-interview-questions'>FullStack.Cafe</a>
 6807 | 
 6808 | ## [[⬆]](#toc) <a name=40CommonADO.NETInterviewQuestionstoKnowin2019>40 Common ADO.NET Interview Questions to Know in 2019</a>
 6809 | > Originally published on 👉 <a href='https://www.fullstack.cafe\blog\ado-net-interview-questions'>40 Common ADO.NET Interview Questions to Know in 2019 | FullStack.Cafe</a>
 6810 | 
 6811 | #### Q1: What is ADO.NET? ⭐
 6812 | **Answer:**
 6813 | **ADO** stands for Active Data Object and ADO.NET is a set of .NET libraries for ADO.
 6814 | NET is a collection of managed libraries used by .NET applications for data source communication using a driver or provider:
 6815 | 
 6816 | *   Enterprise applications handle a large amount of data. This data is primarily stored in relational databases, such as Oracle, SQL Server, and Access and so on. These databases use Structured Query Language (SQL) for retrieval of data.  
 6817 | *   To access enterprise data from a .NET application, an interface was needed. This interface acts as a bridge between an RDBMS system and a .NET application. ADO.NET is such an interface that is created to connect .NET applications to RDBMS systems.  
 6818 | *   In the .NET framework, Microsoft introduced a new version of Active X Data Objects (ADO) called ADO.NET. Any .NET application, either Windows based or web based, can interact with the database using a rich set of classes of the ADO.NET library. Data can be accessed from any database using connected or disconnected architecture.
 6819 | 
 6820 | **Source:** _c-sharpcorner.com_
 6821 | 
 6822 | #### Q2: What do you understand by DataRelation class? ⭐⭐
 6823 | **Answer:**
 6824 | The **DataRelation** is a class of disconnected architecture in the .NET framework. It is found in the System.Data namespace. It represents a relationship between database tables and correlates tables on the basis of matching column.
 6825 | 
 6826 | **Source:** _c-sharpcorner.com_
 6827 | 
 6828 | #### Q3: Describe when you would use the DataView in ADO.NET? ⭐⭐
 6829 | **Answer:**
 6830 | A **DataView** enables you to create different views of the data stored in a DataTable, a capability that is often used in data binding applications. Using a DataView, you can expose the data in a table with different sort orders, and you can filter the data by row state or based on a filter expression. A DataView provides a dynamic view of data whose content, ordering, and membership reflect changes to the underlying DataTable as they occur. This is different from the Select method of the DataTable, which returns a DataRow array from a table per particular filter and/or sort order and whose content reflects changes to the underlying table, but whose membership and ordering remain static. The dynamic capabilities of the DataView make it ideal for data-binding applications.
 6831 | 
 6832 | **Source:** _stackoverflow.com_
 6833 | 
 6834 | #### Q4: What is the SqlCommandBuilder? ⭐⭐
 6835 | **Answer:**
 6836 | **CommandBuilder** helps you to generate update, delete, and insert commands on a single database table for a data adapter. Similar to other objects, each data provider has a command builder class. The OleDbCommandBuilder, SqlCommonBuilder, and OdbcCommandBuilder classes represent the CommonBuilder object in the OleDb, Sql, and ODBC data providers.
 6837 | 
 6838 | **Source:** _c-sharpcorner.com_
 6839 | 
 6840 | #### Q5: What is the basic difference between ADO.NET and Entity Framework? ⭐⭐
 6841 | **Answer:**
 6842 | ADO.NET Entity Framework is an ORM (object-relational mapping) which creates a higher abstract object model over ADO.NET components. ADO.NET is a layer closer to the database (datatables, datasets and etc...). The main and the only benefit of EF is it auto-generates code for the Model (middle layer), Data Access Layer, and mapping code, thus reducing a lot of development time. Consider the following example:
 6843 | 
 6844 | **ADO.NET**:
 6845 | ```csharp
 6846 | DataTable table = adoDs.Tables[0];
 6847 | for (int j = 0; j < table.Rows.Count; j++)
 6848 | {
 6849 |     DataRow row = table.Rows[j];
 6850 | 
 6851 |     // Get the values of the fields
 6852 |     string CustomerName =
 6853 |         (string)row["Customername"];
 6854 |     string CustomerCode =
 6855 |         (string)row["CustomerCode"];
 6856 | }
 6857 | ```
 6858 | 
 6859 | **EF**:
 6860 | ```csharp
 6861 | foreach (Customer objCust in obj.Customers)
 6862 | {}
 6863 | ```
 6864 | 
 6865 | **Source:** _stackoverflow.com_
 6866 | 
 6867 | #### Q6: What is SqlCommand Object? ⭐⭐
 6868 | **Answer:**
 6869 | The **SqlCommand** carries the SQL statement that needs to be executed on the database. SqlCommand carries the command in the CommandText property and this property will be used when the SqlCommand calls any of its execute methods.
 6870 | 
 6871 | *   The Command Object uses the connection object to execute SQL queries.
 6872 | *   The queries can be in the form of Inline text, Stored Procedures or direct Table access.
 6873 | *   An important feature of Command object is that it can be used to execute queries and Stored Procedures with Parameters.
 6874 | *   If a select query is issued, the result set it returns is usually stored in either a DataSet or a DataReader object.
 6875 | 
 6876 | The three important methods exposed by the SqlCommand object is shown below:
 6877 | 
 6878 | *   ExecuteScalar
 6879 | *   ExecuteNonQuery
 6880 | *   ExecuteReader
 6881 | 
 6882 | **Source:** _c-sharpcorner.com_
 6883 | 
 6884 | #### Q7: What is Connection Pooling in ADO.NET? ⭐⭐
 6885 | **Answer:**
 6886 | ADO.NET uses a technique called **connection pooling**, which minimizes the cost of repeatedly opening and closing connections. Connection pooling reuses existing active connections with the same connection string instead of creating new connections when a request is made to the database. It involves the use of a connection manager that is responsible for maintaining a list, or pool, of available connections for a given connection string. Several pools exist if different connection strings ask for connection pooling.
 6887 | 
 6888 | **Source:** _c-sharpcorner.com_
 6889 | 
 6890 | #### Q8: How can you define the DataSet structure? ⭐⭐
 6891 | **Answer:**
 6892 | A **DataSet** object falls in disconnected components series. The `DataSet` consists of a collection of tables, rows, columns and relationships.
 6893 | 
 6894 | `DataSet` contains a collection of `DataTables` and the `DataTable` contains a collection of `DataRows`, `DataRelations`, and `DataColumns`. A `DataTable` maps to a table in the database.
 6895 | 
 6896 | **Source:** _c-sharpcorner.com_
 6897 | 
 6898 | #### Q9: What are the ADO.NET components? ⭐⭐
 6899 | **Answer:**
 6900 | ADO.NET components categorized in three modes: 
 6901 | * disconnected, 
 6902 | * common or shared and 
 6903 | * the .NET data providers.
 6904 | 
 6905 | The disconnected components build the basic ADO.NET architecture. You can use these components (or classes) with or without data providers. For example, you can use a `DataTable` object with or without providers and shared or common components are the base classes for data providers. Shared or common components are the base classes for data providers and shared by all data providers. The data provider components are specifically designed to work with different kinds of data sources. For example, ODBC data providers work with ODBC data sources and OleDb data providers work with OLE-DB data sources.
 6906 | 
 6907 | **Source:** _c-sharpcorner.com_
 6908 | 
 6909 | #### Q10: What is exactly meaning of disconnected and connected approach in ADO.NET? ⭐⭐
 6910 | **Answer:**
 6911 | In short:
 6912 | * **Disconnected** = Make Connection , Fetch Data , Close Connection
 6913 | * **Connected** = Make Connection , Keep Connection alive , Close Connection when close is called.
 6914 | 
 6915 | The ADO.net architecture, in which connection must be kept open till the end to retrieve and access data from database is called as _connected architecture_. Connected architecture is built on the these types - `connection`, `command`, `datareader`
 6916 | 
 6917 | The ADO.net architecture, in which connection will be kept open only till the data retrieved from database, and later can be accessed even when connection to database is closed is called as _disconnected architecture_. Disconnected architecture of ADO.net is built on these types - `connection`, `dataadapter`, `commandbuilder` and `dataset` and `dataview`. 
 6918 | 
 6919 | **Source:** _stackoverflow.com_
 6920 | 
 6921 | #### Q11: Mention what is the difference between ADO.NET and classic ADO? ⭐⭐⭐
 6922 | **Answer:**
 6923 | *   In NET, we have data-set while ADO we have record-set
 6924 | *   In record-set we can only have one table and to insert more than one table you have to do inner join. While the dataset in ADO.NET can have multiple tables
 6925 | *   In NET, all data persist in XML while in classic ADO the data persists in binary format also
 6926 | 
 6927 | **Source:** _career.guru99.com_
 6928 | 
 6929 | #### Q12: Could you explain me some of the main differences between Connection-oriented access and connectionless access in ADO.NET? ⭐⭐⭐
 6930 | **Answer:**
 6931 | * **Connection Oriented means** : connection is exist throw out your process.
 6932 | Example : using DataReader in Ado.Net you can get data as connection oriented database connection type.
 6933 | * **Connection Less means** : Your connection is not available throw out your whole process.
 6934 | Example: using DataAdapter in Ado.Net you can get data as connection less database connection type.
 6935 | 
 6936 | **Source:** _stackoverflow.com_
 6937 | 
 6938 | #### Q13: What is the difference between Integrated Security = True and Integrated Security = SSPI? ⭐⭐⭐
 6939 | **Answer:**
 6940 | To connect to the database server is recommended to use Windows Authentication, commonly known as _integrated security_. To specify the Windows authentication, you can use any of the following two key-value pairs with the data provider. NET Framework for SQL Server:
 6941 | 
 6942 | ```sh
 6943 | Integrated Security = true;
 6944 | Integrated Security = SSPI;
 6945 | ```
 6946 | 
 6947 | However, only the second works with the data provider *.NET Framework OleDb*. If you set `Integrated Security = true` for ConnectionString an exception is thrown.
 6948 | 
 6949 | **Source:** _stackoverflow.com_
 6950 | 
 6951 | #### Q14: What is Unit Of Work? ⭐⭐⭐
 6952 | **Answer:**
 6953 | **Unit of Work** is referred to as a single transaction that involves multiple operations of insert/update/delete and so on kinds. To say it in simple words, it means that for a specific user action (say registration on a website), all the transactions like insert/update/delete and so on are done in one single transaction, rather than doing multiple database transactions. 
 6954 | 
 6955 | **Source:** _c-sharpcorner.com_
 6956 | 
 6957 | #### Q15: How could you control connection pooling behavior?  ⭐⭐⭐
 6958 | **Answer:**
 6959 | You can manage connection pools using certain keywords in your connection string. The important ones include the following:
 6960 | * ConnectionTimeout -- this is used to specify the wait period (in seconds) when a new database connection is requested for. The default value is 15.
 6961 | * MinPoolSize -- this represents the minimum number of connections in the pool.
 6962 | * MaxPoolSize -- this represents the maximum number of connections in the pool. The default value is 100.
 6963 | * Pooling -- this controls if connection pooling is turned on or off and can have a value of true of false. When this is set to true, the requested connection is retrieved from the appropriate connection pool.
 6964 | 
 6965 | **Source:** _infoworld.com_
 6966 | 
 6967 | #### Q16: What are the differences between using SqlDataAdapter vs SqlDataReader for getting data from a DB? ⭐⭐⭐
 6968 | **Answer:**
 6969 | **SqlDataReader**:
 6970 | 
 6971 |  * Holds the connection open until you are finished (don't forget to close it or use using).
 6972 |  * Can typically only be iterated over once
 6973 |  * Is not as useful for updating back to the database
 6974 | 
 6975 | On the other hand, it:
 6976 | 
 6977 |  * Only has one record in memory at a time rather than an entire result set (this can be huge)
 6978 |  * Is about as fast as you can get for that one iteration
 6979 |  * Allows you start processing results sooner (once the first record is available)
 6980 | 
 6981 | **SqlDataAdapter/DataSet**:
 6982 | 
 6983 |  * Lets you close the connection as soon it's done loading data, and may even close it for you automatically
 6984 |  * All of the results are available in memory
 6985 |  * You can iterate over it as many times as you need, or even look up a specific record by index
 6986 |  * Has some built-in faculties for updating back to the database
 6987 |  
 6988 | At the cost of:
 6989 | 
 6990 |  * _Much_ higher memory use
 6991 |  * You wait until all the data is loaded before using any of it
 6992 |  
 6993 | So really it depends on what you're doing, but I tend to prefer a DataReader until I need something that's only supported by a dataset.  SqlDataReader is perfect for the common data access case of binding to a read-only grid.
 6994 | 
 6995 | **Source:** _stackoverflow.com_
 6996 | 
 6997 | #### Q17: What is the difference between DataView, DataTable and DataSet? ⭐⭐⭐
 6998 | **Answer:**
 6999 | * A **DataTable** is a collection of DataRows whose DataColumns satisfy a particular schema and may be subject to certain Constraints. As such, it is normally used as an 'in memory' representation of the rows, columns and constraints of a relational database table.
 7000 | * A **DataSet** is a collection of DataTables and DataRelations between them. As such, it can be used to represent all the tables within a relational database file and the parent/child relationships between them.
 7001 | * A **DataView** is a customized view of a DataTable for sorting, filtering, searching, editing, and navigation. It corresponds to a view (i.e. a virtual table produced by a query) in a relational database.
 7002 | 
 7003 | **Source:** _c-sharpcorner.com_
 7004 | 
 7005 | #### Q18: What is the difference between ExecuteScalar, ExecuteReader and ExecuteNonQuery? ⭐⭐⭐
 7006 | **Answer:**
 7007 |   * `ExecuteScalar` is typically used when your query returns a single value.  If it returns more, then the result is the first column of the first row. An example might be `SELECT @@IDENTITY AS 'Identity'`.
 7008 |   * `ExecuteReader` is used for any result set with multiple rows/columns (e.g., `SELECT col1, col2 from sometable`).
 7009 |   * `ExecuteNonQuery` is typically used for SQL statements without results (e.g., UPDATE, INSERT, etc.).
 7010 | 
 7011 | **Source:** _stackoverflow.com_
 7012 | 
 7013 | #### Q19: What is the difference between OLE DB and ODBC data sources? ⭐⭐⭐⭐
 7014 | **Answer:**
 7015 | Read Full Answer on 👉 <a href='https://www.fullstack.cafe\blog\ado-net-interview-questions'>FullStack.Cafe</a>
 7016 | 
 7017 | #### Q20: What is the difference between ADODB, OLEDB and ADO.NET? ⭐⭐⭐⭐
 7018 | **Answer:**
 7019 | Read Full Answer on 👉 <a href='https://www.fullstack.cafe\blog\ado-net-interview-questions'>FullStack.Cafe</a>
 7020 | 
 7021 | #### Q21: How could you monitor connection pooling behavior? ⭐⭐⭐⭐
 7022 | **Answer:**
 7023 | Read Full Answer on 👉 <a href='https://www.fullstack.cafe\blog\ado-net-interview-questions'>FullStack.Cafe</a>
 7024 | 
 7025 | #### Q22: Can you explain the difference between a DataReader, a DataAdapter, a Dataset, and a DataView? ⭐⭐⭐⭐
 7026 | **Answer:**
 7027 | Read Full Answer on 👉 <a href='https://www.fullstack.cafe\blog\ado-net-interview-questions'>FullStack.Cafe</a>
 7028 | 
 7029 | #### Q23: Where should I use disconnected architecture approach? ⭐⭐⭐⭐
 7030 | **Answer:**
 7031 | Read Full Answer on 👉 <a href='https://www.fullstack.cafe\blog\ado-net-interview-questions'>FullStack.Cafe</a>
 7032 | 
 7033 | #### Q24: Where should I use connected architecture approach? ⭐⭐⭐⭐
 7034 | **Answer:**
 7035 | Read Full Answer on 👉 <a href='https://www.fullstack.cafe\blog\ado-net-interview-questions'>FullStack.Cafe</a>
 7036 | 
 7037 | #### Q25: Is there anything faster than SqlDataReader in .NET? ⭐⭐⭐⭐
 7038 | **Answer:**
 7039 | Read Full Answer on 👉 <a href='https://www.fullstack.cafe\blog\ado-net-interview-questions'>FullStack.Cafe</a>
 7040 | 
 7041 | #### Q26: Is it necessary to manually close and dispose of SqlDataReader? ⭐⭐⭐⭐
 7042 | **Answer:**
 7043 | Read Full Answer on 👉 <a href='https://www.fullstack.cafe\blog\ado-net-interview-questions'>FullStack.Cafe</a>
 7044 | 
 7045 | #### Q27: What's better: DataSet or DataReader? ⭐⭐⭐⭐
 7046 | **Answer:**
 7047 | Read Full Answer on 👉 <a href='https://www.fullstack.cafe\blog\ado-net-interview-questions'>FullStack.Cafe</a>
 7048 | 
 7049 | #### Q28: Could you explain some benefits of Repository Pattern? ⭐⭐⭐⭐
 7050 | **Answer:**
 7051 | Read Full Answer on 👉 <a href='https://www.fullstack.cafe\blog\ado-net-interview-questions'>FullStack.Cafe</a>
 7052 | 
 7053 | #### Q29: Name types of transactions in ADO.NET ⭐⭐⭐⭐
 7054 | **Answer:**
 7055 | Read Full Answer on 👉 <a href='https://www.fullstack.cafe\blog\ado-net-interview-questions'>FullStack.Cafe</a>
 7056 | 
 7057 | #### Q30: Name some problems that could occur with connection pooling ⭐⭐⭐⭐⭐
 7058 | **Answer:**
 7059 | Read Full Answer on 👉 <a href='https://www.fullstack.cafe\blog\ado-net-interview-questions'>FullStack.Cafe</a>
 7060 | 
 7061 | #### Q31: What are the advantages of using Stored Procedures? ⭐⭐⭐
 7062 | **Answer:**
 7063 | * Stored procedure can reduced network traffic and latency, boosting application performance.
 7064 | * Stored procedure execution plans can be reused, staying cached in SQL Server's memory, reducing server overhead.
 7065 | * Stored procedures help promote code reuse.
 7066 | * Stored procedures can encapsulate logic. You can change stored procedure code without affecting clients.
 7067 | * Stored procedures provide better security to your data.	
 7068 | 	
 7069 | 
 7070 | **Source:** _github.com/dhaval1406_
 7071 | 
 7072 | #### Q32: What is Denormalization? ⭐⭐⭐
 7073 | **Answer:**
 7074 | It is the process of improving the performance of the database by _adding_ redundant data.
 7075 | 
 7076 | **Source:** _github.com/dhaval1406_
 7077 | 
 7078 | #### Q33: Define ACID Properties ⭐⭐⭐
 7079 | **Answer:**
 7080 | * **Atomicity**: It ensures all-or-none rule for database modifications.
 7081 | * **Consistency**: Data values are consistent across the database.
 7082 | * **Isolation**: Two transactions are said to be independent of one another.
 7083 | * **Durability**: Data is not lost even at the time of server failure.
 7084 | 
 7085 | **Source:** _github.com/chetansomani_
 7086 | 
 7087 | #### Q34: How do I UPDATE from a SELECT in SQL Server? ⭐⭐⭐
 7088 | **Answer:**
 7089 | ```sql
 7090 | UPDATE
 7091 |     Table_A
 7092 | SET
 7093 |     Table_A.col1 = Table_B.col1,
 7094 |     Table_A.col2 = Table_B.col2
 7095 | FROM
 7096 |     Some_Table AS Table_A
 7097 |     INNER JOIN Other_Table AS Table_B
 7098 |         ON Table_A.id = Table_B.id
 7099 | WHERE
 7100 |     Table_A.col3 = 'cool'
 7101 | ```
 7102 | or using `MERGE`:
 7103 | ```sql
 7104 | MERGE INTO YourTable T
 7105 |    USING other_table S 
 7106 |       ON T.id = S.id
 7107 |          AND S.tsql = 'cool'
 7108 | WHEN MATCHED THEN
 7109 |    UPDATE 
 7110 |       SET col1 = S.col1, 
 7111 |           col2 = S.col2;
 7112 | ```
 7113 | 
 7114 | **Source:** _github.com/chetansomani_
 7115 | 
 7116 | #### Q35: Discuss INNER JOIN ON vs WHERE clause ⭐⭐⭐
 7117 | **Details:**
 7118 | You can do:
 7119 | ```sql
 7120 | SELECT
 7121 |     table1.this, table2.that, table2.somethingelse
 7122 | FROM
 7123 |     table1, table2
 7124 | WHERE
 7125 |     table1.foreignkey = table2.primarykey
 7126 |     AND (some other conditions)
 7127 | ```
 7128 | Or else:
 7129 | ```sql
 7130 | SELECT
 7131 |     table1.this, table2.that, table2.somethingelse
 7132 | FROM
 7133 |     table1 INNER JOIN table2
 7134 |     ON table1.foreignkey = table2.primarykey
 7135 | WHERE
 7136 |     (some other conditions)
 7137 | ```
 7138 | What syntax would you choose and why?
 7139 | 
 7140 | **Answer:**
 7141 | `INNER JOIN` is ANSI syntax which you should use. INNER JOIN helps human readability, and that's a top priority. It can also be easily replaced with an OUTER JOIN whenever a need arises.
 7142 | 
 7143 | Implicit joins (with multiple `FROM` tables) become much much more confusing, hard to read, and hard to maintain once you need to start adding more tables to your query. 
 7144 | 
 7145 | **Source:** _stackoverflow.com_
 7146 | 
 7147 | #### Q36: How to generate row number in SQL Without ROWNUM ⭐⭐⭐⭐
 7148 | **Answer:**
 7149 | Read Full Answer on 👉 <a href='https://www.fullstack.cafe\blog\ado-net-interview-questions'>FullStack.Cafe</a>
 7150 | 
 7151 | #### Q37: How does truncate and delete operation effect Identity? ⭐⭐⭐⭐
 7152 | **Answer:**
 7153 | Read Full Answer on 👉 <a href='https://www.fullstack.cafe\blog\ado-net-interview-questions'>FullStack.Cafe</a>
 7154 | 
 7155 | #### Q38: What is Optimistic Locking and Pessimistic locking? ⭐⭐⭐⭐⭐
 7156 | **Answer:**
 7157 | Read Full Answer on 👉 <a href='https://www.fullstack.cafe\blog\ado-net-interview-questions'>FullStack.Cafe</a>
 7158 | 
 7159 | #### Q39: How does database indexing work? ⭐⭐⭐⭐⭐
 7160 | **Answer:**
 7161 | Read Full Answer on 👉 <a href='https://www.fullstack.cafe\blog\ado-net-interview-questions'>FullStack.Cafe</a>
 7162 | 
 7163 | #### Q40: What are some other types of indexes? ⭐⭐⭐⭐⭐
 7164 | **Answer:**
 7165 | Read Full Answer on 👉 <a href='https://www.fullstack.cafe\blog\ado-net-interview-questions'>FullStack.Cafe</a>
 7166 | 
 7167 | ## [[⬆]](#toc) <a name=42AdvancedJavaInterviewQuestionsForSeniorDevelopers>42 Advanced Java Interview Questions For Senior Developers</a>
 7168 | > Originally published on 👉 <a href='https://www.fullstack.cafe\blog\advanced-java-interview-questions'>42 Advanced Java Interview Questions For Senior Developers | FullStack.Cafe</a>
 7169 | 
 7170 | #### Q1: What is the difference between an Interface and an Abstract class?  ⭐⭐
 7171 | **Answer:**
 7172 | Java provides and supports the creation both of **abstract** classes and **interfaces**. Both implementations share some common characteristics, but they differ in the following features:
 7173 | 
 7174 | * All methods in an interface are implicitly abstract. On the other hand, an abstract class may contain both abstract and non-abstract methods.
 7175 | * A class may implement a number of Interfaces, but can extend only one abstract class.
 7176 | * In order for a class to implement an interface, it must implement all its declared methods. However, a class may not implement all declared methods of an abstract class. Though, in this case, the sub-class must also be declared as abstract.
 7177 | * Abstract classes can implement interfaces without even providing the implementation of interface methods.
 7178 | * Variables declared in a Java interface is by default final. An abstract class may contain non-final variables.
 7179 | * Members of a Java interface are public by default. A member of an abstract class can either be private, protected or public.
 7180 | * An interface is absolutely abstract and cannot be instantiated. An abstract class also cannot be instantiated, but can be invoked if it contains a main method.
 7181 | 
 7182 | **Source:** _github.com/snowdream_
 7183 | 
 7184 | #### Q2: What differences exist between HashMap and Hashtable?  ⭐⭐
 7185 | **Answer:**
 7186 | There are several differences between `HashMap` and `Hashtable` in Java:
 7187 | 
 7188 |  1. `Hashtable` is synchronized, whereas `HashMap` is not. This makes `HashMap` better for non-threaded applications, as unsynchronized Objects typically perform better than synchronized ones.
 7189 | 
 7190 |  2. `Hashtable` does not allow `null` keys or values.  `HashMap` allows one `null` key and any number of `null` values.
 7191 | 
 7192 |  3. One of HashMap's subclasses is `LinkedHashMap`, so in the event that you'd want predictable iteration order (which is insertion order by default), you could easily swap out the `HashMap` for a `LinkedHashMap`.  This wouldn't be as easy if you were using `Hashtable`.
 7193 | 
 7194 | **Source:** _stackoverflow.com_
 7195 | 
 7196 | #### Q3: What is the difference between Exception and Error in java? ⭐⭐
 7197 | **Answer:**
 7198 | * An **Error** "indicates serious problems that a reasonable application should not try to catch."
 7199 | * An **Exception** "indicates conditions that a reasonable application might want to catch."
 7200 | 
 7201 | **Source:** _github.com/snowdream_
 7202 | 
 7203 | #### Q4: How does Garbage Collection prevent a Java application from going out of memory? ⭐⭐
 7204 | **Answer:**
 7205 | It doesn’t! Garbage Collection simply cleans up unused memory when an object goes out of scope and is no longer needed. However an application could create a huge number of large objects that causes an `OutOfMemoryError`.
 7206 | 
 7207 | **Source:** _codementor.io_
 7208 | 
 7209 | #### Q5: What is reflection and why is it useful? ⭐⭐
 7210 | **Answer:**
 7211 | The name **reflection** is used to describe code which is able to inspect other code in the same system (or itself) and to make modifications at runtime.
 7212 | 
 7213 | For example, say you have an object of an unknown type in Java, and you would like to call a 'doSomething' method on it if one exists. Java's static typing system isn't really designed to support this unless the object conforms to a known interface, but using reflection, your code can look at the object and find out if it has a method called 'doSomething' and then call it if you want to.
 7214 | 
 7215 | ```java
 7216 | Method method = foo.getClass().getMethod("doSomething", null);
 7217 | method.invoke(foo, null);
 7218 | ```
 7219 | 
 7220 | **Source:** _stackoverflow.com_
 7221 | 
 7222 | #### Q6: What is Function Overriding and Overloading in Java? ⭐⭐
 7223 | **Answer:**
 7224 | * Method **overloading** in Java occurs when two or more methods in the same class have the exact same name, but different parameters. 
 7225 | 
 7226 | ```java
 7227 | class Dog{
 7228 |     public void bark(){
 7229 |         System.out.println("woof ");
 7230 |     }
 7231 |  
 7232 |     //overloading method
 7233 |     public void bark(int num){
 7234 |     	for(int i=0; i<num; i++)
 7235 |     		System.out.println("woof ");
 7236 |     }
 7237 | }
 7238 | ```
 7239 | 
 7240 | * On the other hand, method **overriding** is defined as the case when a child class redefines the same method as a parent class. Overridden methods must have the same name, argument list, and return type. The overriding method may not limit the access of the method it overrides.
 7241 | 
 7242 | ```java
 7243 | class Dog{
 7244 |     public void bark(){
 7245 |         System.out.println("woof ");
 7246 |     }
 7247 | }
 7248 | class Hound extends Dog{
 7249 |     public void sniff(){
 7250 |         System.out.println("sniff ");
 7251 |     }
 7252 |  
 7253 |     public void bark(){
 7254 |         System.out.println("bowl");
 7255 |     }
 7256 | }
 7257 |  
 7258 | public class OverridingTest{
 7259 |     public static void main(String [] args){
 7260 |         Dog dog = new Hound();
 7261 |         dog.bark();
 7262 |     }
 7263 | }
 7264 | ```
 7265 | 
 7266 | 
 7267 | **Source:** _github.com/snowdream_
 7268 | 
 7269 | #### Q7: How can I synchornize two Java processes? ⭐⭐⭐
 7270 | **Answer:**
 7271 | It is not possible to do something like you want in Java. Different Java applications will use different JVM's fully separating themselves into different 'blackbox'es. However, you have 2 options:
 7272 | 
 7273 | * Use sockets (or channels). Basically one application will open the listening socket and start waiting until it receives some signal. The other application will connect there, and send signals when it had completed something. I'd say this is a preferred way used in 99.9% of applications.
 7274 | * You can call `winapi` from Java (on windows).
 7275 | 
 7276 | **Source:** _stackoverflow.com_
 7277 | 
 7278 | #### Q8: What is difference between fail-fast and fail-safe?  ⭐⭐⭐
 7279 | **Answer:**
 7280 | The [Iterator's](http://docs.oracle.com/javase/7/docs/api/java/util/Iterator.html)  fail-safe property works with the clone of the underlying collection and thus, it is not affected by any modification in the collection. All the collection classes in java.util package are fail-fast, while the collection classes in java.util.concurrent are fail-safe. Fail-fast iterators throw a [ConcurrentModificationException](http://examples.javacodegeeks.com/java-basics/exceptions/java-util-concurrentmodificationexception-how-to-handle-concurrent-modification-exception/), while fail-safe iterator never throws such an exception.
 7281 | 
 7282 | **Source:** _github.com/snowdream_
 7283 | 
 7284 | #### Q9: What is the tradeoff between using an unordered array versus an ordered array?  ⭐⭐⭐
 7285 | **Answer:**
 7286 | The major advantage of an ordered array is that the search times have time complexity of O(log n), compared to that of an unordered array, which is O (n). The disadvantage of an ordered array is that the insertion operation has a time complexity of O(n), because the elements with higher values must be moved to make room for the new element. Instead, the insertion operation for an unordered array takes constant time of O(1).
 7287 | 
 7288 | **Source:** _github.com/snowdream_
 7289 | 
 7290 | #### Q10: What is structure of Java Heap? ⭐⭐⭐
 7291 | **Answer:**
 7292 | The JVM has a heap that is the runtime data area from which memory for all class instances and arrays is allocated. It is created at the JVM start-up. Heap memory for objects is reclaimed by an automatic memory management system which is known as a garbage collector. Heap memory consists of live and dead objects. Live objects are accessible by the application and will not be a subject of garbage collection. Dead objects are those which will never be accessible by the application, but have not been collected by the garbage collector yet. Such objects occupy the heap memory space until they are eventually collected by the garbage collector.
 7293 | 
 7294 | **Source:** _github.com/snowdream_
 7295 | 
 7296 | #### Q11: What is the difference between throw and throws? ⭐⭐⭐
 7297 | **Answer:**
 7298 | The `throw` keyword is used to explicitly raise a exception within the program. On the contrary, the `throws` clause is used to indicate those exceptions that are not handled by a method. Each method must explicitly specify which exceptions does not handle, so the callers of that method can guard against possible exceptions. Finally, multiple exceptions are separated by a comma.
 7299 | 
 7300 | **Source:** _github.com/snowdream_
 7301 | 
 7302 | #### Q12: Is Java “pass-by-reference” or “pass-by-value”? ⭐⭐⭐
 7303 | **Answer:**
 7304 | Java is always **pass-by-value**. Unfortunately, when we pass the value of an object, we are passing the _reference_ to it. There is no such thing as "pass-by-reference" in Java. This is confusing to beginners.
 7305 | 
 7306 | The key to understanding this is that something like
 7307 | ```java
 7308 | Dog myDog;
 7309 | ```
 7310 | is not a Dog; it's actually a `pointer` to a Dog.
 7311 | 
 7312 | So when you have
 7313 | ```java
 7314 | Dog myDog = new Dog("Rover");
 7315 | foo(myDog);
 7316 | ```
 7317 | you're essentially passing the address of the created `Dog` object to the `foo` method.
 7318 | 
 7319 | **Source:** _stackoverflow.com_
 7320 | 
 7321 | #### Q13: What is a JavaBean exactly? ⭐⭐⭐
 7322 | **Answer:**
 7323 | Basically, a "Bean" follows the standart:
 7324 | 
 7325 | * is a **serializable** object (that is, it implements `java.io.Serializable`, and does so correctly), that
 7326 | * has "properties" whose getters and setters are just methods with certain names (like, say, getFoo() is the getter for the "Foo" property), and
 7327 | * has a public 0-arg constructor (so it can be created at will and configured by setting its properties).
 7328 | 
 7329 | There is no syntactic difference between a JavaBean and another class - a class is a JavaBean if it follows the standards.
 7330 | 
 7331 | **Source:** _stackoverflow.com_
 7332 | 
 7333 | #### Q14: Can == be used on enum? ⭐⭐⭐
 7334 | **Answer:**
 7335 | **Yes**: enums have tight instance controls that allows you to use == to compare instances. Here's the guarantee provided by the language specification.
 7336 | 
 7337 | **Source:** _stackoverflow.com_
 7338 | 
 7339 | #### Q15: What are the differences between == and equals? ⭐⭐⭐
 7340 | **Answer:**
 7341 | As a reminder, it needs to be said that generally, `==` is NOT a viable alternative to `equals`. When it is, however (such as with enum), there are two important differences to consider:
 7342 | 
 7343 | 1. `==` never throws `NullPointerException`
 7344 | 
 7345 | ```java
 7346 | enum Color { BLACK, WHITE };
 7347 | 
 7348 | Color nothing = null;
 7349 | if (nothing == Color.BLACK);      // runs fine
 7350 | if (nothing.equals(Color.BLACK)); // throws NullPointerEx
 7351 | ```
 7352 | 
 7353 | 2. `==` is subject to type compatibility check at compile time
 7354 | 
 7355 | ```java
 7356 | enum Color { BLACK, WHITE };
 7357 | enum Chiral { LEFT, RIGHT };
 7358 | 
 7359 | if (Color.BLACK.equals(Chiral.LEFT)); // compiles fine
 7360 | if (Color.BLACK == Chiral.LEFT);      // DOESN'T COMPILE!!! Incompatible types!
 7361 | ```
 7362 | 
 7363 | **Source:** _stackoverflow.com_
 7364 | 
 7365 | #### Q16: What is the main difference between StringBuffer and StringBuilder? ⭐⭐⭐
 7366 | **Answer:**
 7367 | * `StringBuffer` is synchronized, `StringBuilder` is not. When some thing is synchronized, then multiple threads can access, and modify it with out any problem or side effect. `StringBuffer` is synchronized, so you can use it with multiple threads with out any problem.
 7368 | 
 7369 | * `StringBuilder` is faster than `StringBuffer` because it's not synchronized. Using synchronized methods in a single thread is overkill.
 7370 | 
 7371 | 
 7372 | **Source:** _stackoverflow.com_
 7373 | 
 7374 | #### Q17: Why does Java have transient fields? ⭐⭐⭐
 7375 | **Answer:**
 7376 | The **transient** keyword in Java is used to indicate that a field should not be part of the serialization.
 7377 | 
 7378 | By default, all of object's variables get converted into a persistent state. In some cases, you may want to avoid persisting some variables because you don't have the need to persist those variables. So you can declare those variables as transient. If the variable is declared as **transient**, then it `will not be persisted`. 
 7379 | 
 7380 | **Source:** _stackoverflow.com_
 7381 | 
 7382 | #### Q18: What is static initializer? ⭐⭐⭐
 7383 | **Details:**
 7384 | 
 7385 | 
 7386 | 
 7387 | **Answer:**
 7388 | The static initializer is a `static {}` block of code inside java class, and run only one time before the constructor or main method is called. If you had to perform a complicated calculation to determine the value of x — or if its value comes from a database — a static initializer could be very useful.
 7389 | 
 7390 | 
 7391 | Consider:
 7392 | ```java
 7393 | class StaticInit {
 7394 |     public static int x;
 7395 |     static {
 7396 |         x = 32;
 7397 |     }
 7398 |     // other class members such as constructors and
 7399 |     // methods go here...
 7400 | }
 7401 | ```
 7402 | 
 7403 | **Source:** _stackoverflow.com_
 7404 | 
 7405 | #### Q19: Is there anything like static class in java? ⭐⭐⭐
 7406 | **Answer:**
 7407 | Java has **no way** of making a top-level class static but you can simulate a static class like this:
 7408 | 
 7409 | * Declare your class final - Prevents extension of the class since extending a static class makes no sense
 7410 | * Make the constructor private - Prevents instantiation by client code as it makes no sense to instantiate a static class
 7411 | * Make all the members and functions of the class static - Since the class cannot be instantiated no instance methods can be called or instance fields accessed
 7412 | * Note that the compiler will not prevent you from declaring an instance (non-static) member. The issue will only show up if you attempt to call the instance member
 7413 | 
 7414 | **Source:** _stackoverflow.com_
 7415 | 
 7416 | #### Q20: What do the ... dots in the method parameters mean? ⭐⭐⭐
 7417 | **Details:**
 7418 | What do the 3 dots in the following method mean?
 7419 | ```java
 7420 | public void myMethod(String... strings){
 7421 |     // method body
 7422 | }
 7423 | ```
 7424 | 
 7425 | **Answer:**
 7426 | That feature is called varargs, and it's a feature introduced in Java 5. It means that function can receive multiple `String` arguments:
 7427 | ```java
 7428 | myMethod("foo", "bar");
 7429 | myMethod("foo", "bar", "baz");
 7430 | myMethod(new String[]{"foo", "var", "baz"}); // you can eve
 7431 | ```
 7432 | Then, you can use the `String` var as an array:
 7433 | ```java
 7434 | public void myMethod(String... strings){
 7435 |     for(String whatever : strings){
 7436 |         // do what ever you want
 7437 |     }
 7438 | 
 7439 |     // the code above is is equivalent to
 7440 |     for( int i = 0; i < strings.length; i++){
 7441 |         // classical for. In this case you use strings[i]
 7442 |     }
 7443 | }
 7444 | ```
 7445 | 
 7446 | **Source:** _stackoverflow.com_
 7447 | 
 7448 | #### Q21: What is the JIT? ⭐⭐⭐
 7449 | **Answer:**
 7450 | The **JIT** is the JVM’s mechanism by which it can optimize code at runtime.
 7451 | 
 7452 | JIT means **Just In Time**. It is a central feature of any JVM. Among other optimizations, it can perform code inlining, lock coarsening or lock eliding, escape analysis etc.
 7453 | 
 7454 | The main benefit of the JIT is on the programmer’s side: code should be written so that it just works; if the code can be optimized at runtime, more often than not, the JIT will find a way.
 7455 | 
 7456 | **Source:** _codementor.io_
 7457 | 
 7458 | #### Q22: What is the difference between a synchronized method and a synchronized block? ⭐⭐⭐⭐
 7459 | **Answer:**
 7460 | Read Full Answer on 👉 <a href='https://www.fullstack.cafe\blog\advanced-java-interview-questions'>FullStack.Cafe</a>
 7461 | 
 7462 | #### Q23: What is the difference between Serial and Throughput Garbage collector? ⭐⭐⭐⭐
 7463 | **Answer:**
 7464 | Read Full Answer on 👉 <a href='https://www.fullstack.cafe\blog\advanced-java-interview-questions'>FullStack.Cafe</a>
 7465 | 
 7466 | #### Q24: Given two double values d1, d2, what is the most reliable way to test their equality?  ⭐⭐⭐⭐
 7467 | **Answer:**
 7468 | Read Full Answer on 👉 <a href='https://www.fullstack.cafe\blog\advanced-java-interview-questions'>FullStack.Cafe</a>
 7469 | 
 7470 | #### Q25: Explain Marshalling and demarshalling. ⭐⭐⭐⭐
 7471 | **Answer:**
 7472 | Read Full Answer on 👉 <a href='https://www.fullstack.cafe\blog\advanced-java-interview-questions'>FullStack.Cafe</a>
 7473 | 
 7474 | #### Q26: Why is char[] preferred over String for passwords? ⭐⭐⭐⭐
 7475 | **Details:**
 7476 | Why does `String` pose a threat to security when it comes to passwords? It feels inconvenient to use `char[]`?
 7477 | 
 7478 | **Answer:**
 7479 | Read Full Answer on 👉 <a href='https://www.fullstack.cafe\blog\advanced-java-interview-questions'>FullStack.Cafe</a>
 7480 | 
 7481 | #### Q27: When to use LinkedList over ArrayList in Java? ⭐⭐⭐⭐
 7482 | **Answer:**
 7483 | Read Full Answer on 👉 <a href='https://www.fullstack.cafe\blog\advanced-java-interview-questions'>FullStack.Cafe</a>
 7484 | 
 7485 | #### Q28: What is Double Brace initialization in Java? ⭐⭐⭐⭐
 7486 | **Answer:**
 7487 | Read Full Answer on 👉 <a href='https://www.fullstack.cafe\blog\advanced-java-interview-questions'>FullStack.Cafe</a>
 7488 | 
 7489 | #### Q29: Is it possible to call one constructor from another in Java? ⭐⭐⭐⭐
 7490 | **Details:**
 7491 | Is it possible to call a constructor from another (within the same class, not from a subclass)? If yes how?
 7492 | 
 7493 | **Answer:**
 7494 | Read Full Answer on 👉 <a href='https://www.fullstack.cafe\blog\advanced-java-interview-questions'>FullStack.Cafe</a>
 7495 | 
 7496 | #### Q30: Does Java support default parameter values? ⭐⭐⭐⭐
 7497 | **Answer:**
 7498 | Read Full Answer on 👉 <a href='https://www.fullstack.cafe\blog\advanced-java-interview-questions'>FullStack.Cafe</a>
 7499 | 
 7500 | #### Q31: Explain a use case for the Builder Design Pattern ⭐⭐⭐⭐
 7501 | **Answer:**
 7502 | Read Full Answer on 👉 <a href='https://www.fullstack.cafe\blog\advanced-java-interview-questions'>FullStack.Cafe</a>
 7503 | 
 7504 | #### Q32: Is null check needed before calling instanceof? ⭐⭐⭐⭐
 7505 | **Details:**
 7506 | Will 
 7507 | 
 7508 | ```java
 7509 | null instanceof SomeClass
 7510 | ```
 7511 | return `false` or throw a `NullPointerException`?
 7512 | 
 7513 | **Answer:**
 7514 | Read Full Answer on 👉 <a href='https://www.fullstack.cafe\blog\advanced-java-interview-questions'>FullStack.Cafe</a>
 7515 | 
 7516 | #### Q33: What exactly is marker interface in Java? ⭐⭐⭐⭐
 7517 | **Answer:**
 7518 | Read Full Answer on 👉 <a href='https://www.fullstack.cafe\blog\advanced-java-interview-questions'>FullStack.Cafe</a>
 7519 | 
 7520 | #### Q34: What does 'synchronized' mean? ⭐⭐⭐⭐⭐
 7521 | **Answer:**
 7522 | Read Full Answer on 👉 <a href='https://www.fullstack.cafe\blog\advanced-java-interview-questions'>FullStack.Cafe</a>
 7523 | 
 7524 | #### Q35: Why ArrayList are preferable in many more use-cases than LinkedList? ⭐⭐⭐⭐⭐
 7525 | **Answer:**
 7526 | Read Full Answer on 👉 <a href='https://www.fullstack.cafe\blog\advanced-java-interview-questions'>FullStack.Cafe</a>
 7527 | 
 7528 | #### Q36: What's wrong with Double Brace initialization in Java? ⭐⭐⭐⭐⭐
 7529 | **Answer:**
 7530 | Read Full Answer on 👉 <a href='https://www.fullstack.cafe\blog\advanced-java-interview-questions'>FullStack.Cafe</a>
 7531 | 
 7532 | #### Q37: Provide some examples when a finally block won't be executed in Java? ⭐⭐⭐⭐⭐
 7533 | **Answer:**
 7534 | Read Full Answer on 👉 <a href='https://www.fullstack.cafe\blog\advanced-java-interview-questions'>FullStack.Cafe</a>
 7535 | 
 7536 | #### Q38: Explain what will the code return ⭐⭐⭐⭐⭐
 7537 | **Details:**
 7538 | Consider:
 7539 | ```java
 7540 | try { return true; } finally { return false; }
 7541 | ```
 7542 | 
 7543 | **Answer:**
 7544 | Read Full Answer on 👉 <a href='https://www.fullstack.cafe\blog\advanced-java-interview-questions'>FullStack.Cafe</a>
 7545 | 
 7546 | #### Q39: What is an efficient way to implement a singleton pattern in Java? ⭐⭐⭐⭐⭐
 7547 | **Answer:**
 7548 | Read Full Answer on 👉 <a href='https://www.fullstack.cafe\blog\advanced-java-interview-questions'>FullStack.Cafe</a>
 7549 | 
 7550 | #### Q40: What's the difference between SoftReference and WeakReference in Java? ⭐⭐⭐⭐⭐
 7551 | **Answer:**
 7552 | Read Full Answer on 👉 <a href='https://www.fullstack.cafe\blog\advanced-java-interview-questions'>FullStack.Cafe</a>
 7553 | 
 7554 | #### Q41: Why isn’t String‘s .length() accurate? ⭐⭐⭐⭐⭐
 7555 | **Answer:**
 7556 | Read Full Answer on 👉 <a href='https://www.fullstack.cafe\blog\advanced-java-interview-questions'>FullStack.Cafe</a>
 7557 | 
 7558 | #### Q42: Compare volatile vs static variables in Java ⭐⭐⭐⭐⭐
 7559 | **Answer:**
 7560 | Read Full Answer on 👉 <a href='https://www.fullstack.cafe\blog\advanced-java-interview-questions'>FullStack.Cafe</a>
 7561 | 
 7562 | ## [[⬆]](#toc) <a name=45ImportantPHPInterviewQuestionsThatMayLandYouaJob>45 Important PHP Interview Questions That May Land You a Job</a>
 7563 | > Originally published on 👉 <a href='https://www.fullstack.cafe\blog\php-interview-questions'>45 Important PHP Interview Questions That May Land You a Job | FullStack.Cafe</a>
 7564 | 
 7565 | #### Q1: What is the difference between == and ===? ⭐
 7566 | **Answer:**
 7567 | * The operator `==` casts between two different types if they are different
 7568 | * The `===` operator performs a '_typesafe comparison_'
 7569 | 
 7570 | That means that it will only return true if both operands have the same type and the same value.
 7571 | 
 7572 | ```php
 7573 | 1 === 1: true
 7574 | 1 == 1: true
 7575 | 1 === "1": false // 1 is an integer, "1" is a string
 7576 | 1 == "1": true // "1" gets casted to an integer, which is 1
 7577 | "foo" === "foo": true // both operands are strings and have the same value
 7578 | ```
 7579 | 
 7580 | **Source:** _stackoverflow.com_
 7581 | 
 7582 | #### Q2: How can you pass a variable by reference? ⭐
 7583 | **Answer:**
 7584 | To be able to pass a variable by **reference**, we use an _ampersand_ in front of it, as follows:
 7585 | ```php
 7586 | $var1 = &$var2
 7587 | ```
 7588 | 
 7589 | **Source:** _guru99.com_
 7590 | 
 7591 | #### Q3: What does $GLOBALS mean? ⭐
 7592 | **Answer:**
 7593 | `$GLOBALS` is associative array including references to all variables which are currently defined in the global scope of the script.
 7594 | 
 7595 | **Source:** _guru99.com_
 7596 | 
 7597 | #### Q4: What is the use of ini_set()? ⭐
 7598 | **Answer:**
 7599 | PHP allows the user to modify some of its settings mentioned in php.ini using ini_set(). This function requires two string arguments. First one is the name of the setting to be modified and the second one is the new value to be assigned to it.
 7600 | 
 7601 | Given line of code will enable the display_error setting for the script if it’s disabled.
 7602 | 
 7603 | `ini_set('display_errors', '1');`
 7604 | 
 7605 | We need to put the above statement, at the top of the script so that, the setting remains enabled till the end. Also, the values set via ini_set() are applicable, only to the current script. Thereafter, PHP will start using the original values from php.ini.
 7606 | 
 7607 | **Source:** _github.com/Bootsity_
 7608 | 
 7609 | #### Q5: When should I use require vs. include? ⭐⭐
 7610 | **Answer:**
 7611 | The `require()` function is identical to `include()`, except that it handles errors differently. If an error occurs, the `include()` function generates a warning, but the script will continue execution. The `require()` generates a fatal error, and the script will stop.
 7612 | 
 7613 | My suggestion is to just use `require_once` 99.9% of the time.
 7614 | 
 7615 | Using `require` or `include` instead implies that your code is not **reusable** elsewhere, i.e. that the scripts you're pulling in actually execute code instead of making available a class or some function libraries.
 7616 | 
 7617 | **Source:** _stackoverflow.com_
 7618 | 
 7619 | #### Q6: What is stdClass in PHP? ⭐⭐
 7620 | **Answer:**
 7621 | `stdClass` is just a generic 'empty' class that's used when casting other types to objects. `stdClass` is **not** the base class for objects in PHP.  This can be demonstrated fairly easily:
 7622 | 
 7623 | ```js
 7624 | class Foo{}
 7625 | $foo = new Foo();
 7626 | echo ($foo instanceof stdClass)?'Y':'N'; // outputs 'N'
 7627 | ```
 7628 | 
 7629 | It is useful for anonymous objects, dynamic properties, etc. 
 7630 | 
 7631 | An easy way to consider the `StdClass` is as an alternative to associative array. See this example below that shows how `json_decode()` allows to get an StdClass instance or an associative array.
 7632 | Also but not shown in this example, `SoapClient::__soapCall` returns an `StdClass` instance.
 7633 | 
 7634 | ```js
 7635 | //Example with StdClass
 7636 | $json = '{ "foo": "bar", "number": 42 }';
 7637 | $stdInstance = json_decode($json);
 7638 | 
 7639 | echo $stdInstance - > foo.PHP_EOL; //"bar"
 7640 | echo $stdInstance - > number.PHP_EOL; //42
 7641 | 
 7642 | //Example with associative array
 7643 | $array = json_decode($json, true);
 7644 | 
 7645 | echo $array['foo'].PHP_EOL; //"bar"
 7646 | echo $array['number'].PHP_EOL; //42
 7647 | ```
 7648 | 
 7649 | 
 7650 | 
 7651 | **Source:** _stackoverflow.com_
 7652 | 
 7653 | #### Q7: What are the differences between die() and exit() functions in PHP? ⭐⭐
 7654 | **Answer:**
 7655 | There's no difference - they are the same. The only advantage of choosing `die()` over `exit()`, might be the time you spare on typing an extra letter.
 7656 | 
 7657 | **Source:** _stackoverflow.com_
 7658 | 
 7659 | #### Q8: What are the main differences between const vs define ⭐⭐
 7660 | **Answer:**
 7661 | The fundamental difference between `const` vs `define` is that `const` defines constants at compile time, whereas `define` defines them at run time.
 7662 | 
 7663 | ```php
 7664 | const FOO = 'BAR';
 7665 | define('FOO', 'BAR');
 7666 | 
 7667 | // but
 7668 | if (...) {
 7669 |     const FOO = 'BAR';    // Invalid
 7670 | }
 7671 | if (...) {
 7672 |     define('FOO', 'BAR'); // Valid
 7673 | }
 7674 | ```
 7675 | 
 7676 | Also until PHP 5.3, `const` could not be used in the global scope. You could only use this from within a class. This should be used when you want to set some kind of constant option or setting that pertains to that class. Or maybe you want to create some kind of enum. An example of good `const` usage is to get rid of magic numbers. 
 7677 | 
 7678 | `Define` can be used for the same purpose, but it can only be used in the global scope. It should only be used for global settings that affect the entire application.
 7679 | 
 7680 | Unless you need any type of conditional or expressional definition, use `consts` instead of `define() `- simply for the sake of readability!
 7681 | 
 7682 | **Source:** _stackoverflow.com_
 7683 | 
 7684 | #### Q9: What's the difference between isset() and array_key_exists()?  ⭐⭐
 7685 | **Answer:**
 7686 | * `array_key_exists` will tell you if a key exists in an array and complains when `$a` does not exist.
 7687 | * `isset` will only return `true` if the key/variable exists **and is not `null`**. `isset` doesn't complain when `$a` does not exist.
 7688 | 
 7689 | Consider:
 7690 | ```js
 7691 | $a = array('key1' => 'Foo Bar', 'key2' => null);
 7692 | 
 7693 | isset($a['key1']);             // true
 7694 | array_key_exists('key1', $a);  // true
 7695 | 
 7696 | isset($a['key2']);             // false
 7697 | array_key_exists('key2', $a);  // true
 7698 | ```
 7699 | 
 7700 | **Source:** _stackoverflow.com_
 7701 | 
 7702 | #### Q10: What is the difference between var_dump() and print_r()? ⭐⭐
 7703 | **Answer:**
 7704 | * The `var_dump` function displays structured information about variables/expressions including its **type** and **value**. Arrays are explored recursively with values indented to show structure. It also shows which array values and object properties are references.
 7705 | 
 7706 | * The `print_r()` displays information about a variable in a way that's readable by humans. array values will be presented in a format that shows keys and elements. Similar notation is used for objects.
 7707 | 
 7708 | Consider:
 7709 | ```php
 7710 | $obj = (object) array('qualitypoint', 'technologies', 'India');
 7711 | ```
 7712 | `var_dump($obj) `will display below output in the screen:
 7713 | ```
 7714 | object(stdClass)#1 (3) {
 7715 |  [0]=> string(12) "qualitypoint"
 7716 |  [1]=> string(12) "technologies"
 7717 |  [2]=> string(5) "India"
 7718 | }
 7719 | ```
 7720 | And, `print_r($obj)` will display below output in the screen.
 7721 | ```
 7722 | stdClass Object ( 
 7723 |  [0] => qualitypoint
 7724 |  [1] => technologies
 7725 |  [2] => India
 7726 | )
 7727 | ```
 7728 | 
 7729 | **Source:** _stackoverflow.com_
 7730 | 
 7731 | #### Q11: Explain what the different PHP errors are ⭐⭐
 7732 | **Answer:**
 7733 | * A `notice` is a non-critical error saying something went wrong in execution, something minor like an undefined variable.
 7734 | * A `warning` is given when a more critical error like if an include() command went to retrieve a non-existent file. In both this and the error above, the script would continue.
 7735 | * A `fatal error` would terminate the code. Failure to satisfy a require() would generate this type of error, for example.
 7736 | 
 7737 | **Source:** _pangara.com_
 7738 | 
 7739 | #### Q12: How can you enable error reporting in PHP? ⭐⭐
 7740 | **Answer:**
 7741 | Check if “`display_errors`” is equal “on” in the php.ini or declare “`ini_set('display_errors', 1)`” in your script.
 7742 | 
 7743 | Then, include “`error_reporting(E_ALL)`” in your code to display all types of error messages during the script execution.
 7744 | 
 7745 | **Source:** _codementor.io_
 7746 | 
 7747 | #### Q13: Declare some function with default parameter ⭐⭐
 7748 | **Answer:**
 7749 | Consider:
 7750 | ```php
 7751 | function showMessage($hello = false){
 7752 |   echo ($hello) ? 'hello' : 'bye';
 7753 | }
 7754 | ```
 7755 | 
 7756 | **Source:** _codementor.io_
 7757 | 
 7758 | #### Q14:  Is multiple inheritance supported in PHP? ⭐⭐
 7759 | **Answer:**
 7760 | PHP supports only single inheritance; it means that a class can be extended from only one single class using the keyword 'extended'.
 7761 | 
 7762 | **Source:** _guru99.com_
 7763 | 
 7764 | #### Q15: In PHP, objects are they passed by value or by reference? ⭐⭐
 7765 | **Answer:**
 7766 | In PHP, objects passed by **value**.
 7767 | 
 7768 | **Source:** _guru99.com_
 7769 | 
 7770 | #### Q16: What is the differences between $a != $b and $a !== $b? ⭐⭐
 7771 | **Answer:**
 7772 | `!=` means _inequality_ (TRUE if $a is not equal to $b) and `!==` means _non-identity_ (TRUE if $a is not identical to $b).
 7773 | 
 7774 | **Source:** _guru99.com_
 7775 | 
 7776 | #### Q17: What is PDO in PHP? ⭐⭐
 7777 | **Answer:**
 7778 | **PDO** stands for PHP Data Object.
 7779 | 
 7780 | It is a set of PHP extensions that provide a core PDO class and database, specific drivers. It provides a vendor-neutral, lightweight, data-access abstraction layer. Thus, no matter what database we use, the function to issue queries and fetch data will be same. It focuses on data access abstraction rather than database abstraction.
 7781 | 
 7782 | **Source:** _github.com/Bootsity_
 7783 | 
 7784 | #### Q18: Explain how we handle exceptions in PHP? ⭐⭐
 7785 | **Answer:**
 7786 | When an exception is thrown, code following the statement will not be executed, and PHP will attempt to find the first matching catch block. If an exception is not caught, a PHP Fatal Error will be issued with an "Uncaught Exception".
 7787 | An exception can be thrown, and caught within PHP. 
 7788 | 
 7789 | To handle exceptions, code may be surrounded in a `try` block.
 7790 | Each try must have at least one corresponding `catch` block. Multiple catch blocks can be used to catch different classes of exceptions.
 7791 | Exceptions can be thrown (or re-thrown) within a catch block.
 7792 | 
 7793 | Consider:
 7794 | 
 7795 | ```php
 7796 | try {
 7797 |     print "this is our try block n";
 7798 |     throw new Exception();
 7799 | } catch (Exception $e) {
 7800 |     print "something went wrong, caught yah! n";
 7801 | } finally {
 7802 |     print "this part is always executed n";
 7803 | }
 7804 | ```
 7805 | 
 7806 | **Source:** _github.com/Bootsity_
 7807 | 
 7808 | #### Q19: Differentiate between echo and print() ⭐⭐
 7809 | **Answer:**
 7810 | `echo` and `print` are more or less the same. They are both used to output data to the screen.
 7811 | 
 7812 | The differences are: 
 7813 | - echo has no return value while print has a return value of 1 so it can be used in expressions. 
 7814 | - echo can take multiple parameters (although such usage is rare) while print can take one argument. 
 7815 | - echo is faster than print.
 7816 | 
 7817 | **Source:** _github.com/Bootsity_
 7818 | 
 7819 | #### Q20: When should I use require_once vs. require? ⭐⭐⭐
 7820 | **Answer:**
 7821 | The `require_once()` statement is identical to `require()` except PHP will check if the file has already been included, and if so, not include (require) it again.
 7822 | 
 7823 | My suggestion is to just use `require_once` 99.9% of the time.
 7824 | 
 7825 | Using `require` or `include` instead implies that your code is not **reusable** elsewhere, i.e. that the scripts you're pulling in actually execute code instead of making available a class or some function libraries.
 7826 | 
 7827 | 
 7828 | 
 7829 | **Source:** _stackoverflow.com_
 7830 | 
 7831 | #### Q21: Check if PHP array is associative ⭐⭐⭐
 7832 | **Answer:**
 7833 | Consider:
 7834 | ```php
 7835 | function has_string_keys(array $array) {
 7836 |   return count(array_filter(array_keys($array), 'is_string')) > 0;
 7837 | }
 7838 | ```
 7839 | If there is at least one string key, `$array` will be regarded as an _associative array_.
 7840 | 
 7841 | **Source:** _stackoverflow.com_
 7842 | 
 7843 | #### Q22: How do I pass variables and data from PHP to JavaScript? ⭐⭐⭐
 7844 | **Answer:**
 7845 | There are actually several approaches to do this:
 7846 | * Use AJAX to get the data you need from the server.
 7847 | <br/>Consider **get-data.php**:
 7848 | ```php
 7849 | echo json_encode(42);
 7850 | ```
 7851 | Consider **index.html:**
 7852 | ```js
 7853 | <script>
 7854 |     function reqListener () {
 7855 |       console.log(this.responseText);
 7856 |     }
 7857 | 
 7858 |     var oReq = new XMLHttpRequest(); // New request object
 7859 |     oReq.onload = function() {
 7860 |         // This is where you handle what to do with the response.
 7861 |         // The actual data is found on this.responseText
 7862 |         alert(this.responseText); // Will alert: 42
 7863 |     };
 7864 |     oReq.open("get", "get-data.php", true);
 7865 |     //                               ^ Don't block the rest of the execution.
 7866 |     //                                 Don't wait until the request finishes to
 7867 |     //                                 continue.
 7868 |     oReq.send();
 7869 | </script>
 7870 | ```
 7871 | * Echo the data into the page somewhere, and use JavaScript to get the information from the DOM.
 7872 | ```php
 7873 | <div id="dom-target" style="display: none;">
 7874 |     <?php
 7875 |         $output = "42"; // Again, do some operation, get the output.
 7876 |         echo htmlspecialchars($output); /* You have to escape because the result
 7877 |                                            will not be valid HTML otherwise. */
 7878 |     ?>
 7879 | </div>
 7880 | <script>
 7881 |     var div = document.getElementById("dom-target");
 7882 |     var myData = div.textContent;
 7883 | </script>
 7884 | ```
 7885 | * Echo the data directly to JavaScript.
 7886 | ```php
 7887 | <script>
 7888 |     var data = <?php echo json_encode("42", JSON_HEX_TAG); ?>; // Don't forget the extra semicolon!
 7889 | </script>
 7890 | ```
 7891 | 
 7892 | **Source:** _stackoverflow.com_
 7893 | 
 7894 | #### Q23: Is there a function to make a copy of a PHP array to another? ⭐⭐⭐
 7895 | **Answer:**
 7896 | In PHP arrays are assigned by copy, while objects are assigned by reference so PHP will copy the array by default. References in PHP have to be explicit:
 7897 | 
 7898 | ```php
 7899 | $a = array(1,2);
 7900 | $b = $a; // $b will be a different array
 7901 | $c = &$a; // $c will be a reference to $a
 7902 | ```
 7903 | 
 7904 | **Source:** _stackoverflow.com_
 7905 | 
 7906 | #### Q24: What will be returned by this code? ⭐⭐⭐
 7907 | **Details:**
 7908 | Consider the code:
 7909 | ```php
 7910 | $a = new stdClass();
 7911 | $a->foo = "bar";
 7912 | $b = clone $a;
 7913 | var_dump($a === $b);
 7914 | ```
 7915 | What will be echoed to the console?
 7916 | 
 7917 | **Answer:**
 7918 | Two instances of the same class with equivalent members do NOT match the `===` operator. So the answer is:
 7919 | 
 7920 | ```php
 7921 | bool(false)
 7922 | ```
 7923 | 
 7924 | **Source:** _stackoverflow.com_
 7925 | 
 7926 | #### Q25: What will be returned by this code? Explain the result. ⭐⭐⭐
 7927 | **Details:**
 7928 | Consider the code. What will be returned as a result?
 7929 | ```php
 7930 | $something = 0;
 7931 | echo ('password123' == $something) ? 'true' : 'false';
 7932 | ```
 7933 | 
 7934 | **Answer:**
 7935 | The answer is `true`. You should never use `==` for string comparison. Even if you are comparing strings to strings, PHP will implicitly cast them to floats and do a numerical comparison if they appear numerical. `===` is OK. 
 7936 | 
 7937 | For example 
 7938 | 
 7939 | ```php
 7940 | '1e3' == '1000' // true
 7941 | ```
 7942 | 
 7943 | also returns true.
 7944 | 
 7945 | **Source:** _stackoverflow.com_
 7946 | 
 7947 | #### Q26: What exactly is the the difference between array_map, array_walk and array_filter? ⭐⭐⭐
 7948 | **Answer:**
 7949 | * `array_walk` takes an array and a function F and modifies it by replacing every element x with F(x).
 7950 | * `array_map` does the exact same thing **except** that instead of modifying in-place it will return a new array with the transformed elements.
 7951 | * `array_filter` with function F, instead of transforming the elements, will remove any elements for which F(x) **is not true**
 7952 | 
 7953 | **Source:** _stackoverflow.com_
 7954 | 
 7955 | #### Q27: Explain the difference between exec() vs system() vs passthru()? ⭐⭐⭐
 7956 | **Answer:**
 7957 | * `exec()` is for calling a system command, and perhaps dealing with the output yourself.
 7958 | * `system()` is for executing a system command and immediately displaying the output - presumably text.
 7959 | * `passthru()` is for executing a system command which you wish the raw return from - presumably something binary.
 7960 | 
 7961 | **Source:** _stackoverflow.com_
 7962 | 
 7963 | #### Q28: How would you create a Singleton class using PHP? ⭐⭐⭐
 7964 | **Answer:**
 7965 | ```php
 7966 | /**
 7967 |  * Singleton class
 7968 |  *
 7969 |  */
 7970 | final class UserFactory {
 7971 |     /**
 7972 |      * Call this method to get singleton
 7973 |      *
 7974 |      * @return UserFactory
 7975 |      */
 7976 |     public static
 7977 |     function Instance() {
 7978 |         static $inst = null;
 7979 |         if ($inst === null) {
 7980 |             $inst = new UserFactory();
 7981 |         }
 7982 |         return $inst;
 7983 |     }
 7984 | 
 7985 |     /**
 7986 |      * Private ctor so nobody else can instantiate it
 7987 |      *
 7988 |      */
 7989 |     private
 7990 |     function __construct() {
 7991 | 
 7992 |     }
 7993 | }
 7994 | ```
 7995 | To use:
 7996 | 
 7997 | ```php
 7998 | $fact = UserFactory::Instance();
 7999 | $fact2 = UserFactory::Instance();
 8000 | ```
 8001 | 
 8002 | But:
 8003 | 
 8004 | ```php
 8005 | $fact = new UserFactory()
 8006 | ```
 8007 | 
 8008 | Throws an error.
 8009 | 
 8010 | **Source:** _stackoverflow.com_
 8011 | 
 8012 | #### Q29: What is the difference between PDO's query() vs execute()? ⭐⭐⭐
 8013 | **Answer:**
 8014 | * `query` runs a standard SQL statement and requires you to properly escape all data to avoid SQL Injections and other issues.
 8015 | * `execute` runs a prepared statement which allows you to bind parameters to avoid the need to escape or quote the parameters. execute will also perform better if you are repeating a query multiple times.
 8016 | 
 8017 | Best practice is to stick with prepared statements and execute for increased _security_. Aside from the escaping on the client-side that it provides, a _prepared statement is compiled_ on the server-side once, and then can be passed different parameters at each execution.
 8018 | 
 8019 | **Source:** _stackoverflow.com_
 8020 | 
 8021 | #### Q30: What is use of Null Coalesce Operator? ⭐⭐⭐
 8022 | **Answer:**
 8023 | Null coalescing operator returns its first operand if it exists and is not NULL. Otherwise it returns its second operand.
 8024 | 
 8025 | Example:
 8026 | 
 8027 | ```php
 8028 | $name = $firstName ?? $username ?? $placeholder ?? "Guest"; 
 8029 | ```
 8030 | 
 8031 | **Source:** _github.com/Bootsity_
 8032 | 
 8033 | #### Q31: Differentiate between exception and error ⭐⭐⭐
 8034 | **Answer:**
 8035 | - Recovering from `Error` is not possible. The only solution to errors is to terminate the execution. Where as you can recover from `Exception` by using either try-catch blocks or throwing exception back to caller.
 8036 | - You will not be able to handle the `Errors` using try-catch blocks. Even if you handle them using try-catch blocks, your application will not recover if they happen. On the other hand, `Exceptions` can be handled using try-catch blocks and can make program flow normal if they happen.
 8037 | - `Exceptions` are related to application where as `Errors` are related to environment in which application is running.
 8038 | 
 8039 | **Source:** _github.com/Bootsity_
 8040 | 
 8041 | #### Q32: What are the exception class functions? ⭐⭐⭐
 8042 | **Answer:**
 8043 | There are following functions which can be used from `Exception` class.
 8044 | * `getMessage()` − message of exception
 8045 | * `getCode()` − code of exception
 8046 | * `getFile()` − source filename
 8047 | * `getLine()` − source line
 8048 | * `getTrace()` − n array of the `backtrace()`
 8049 | * `getTraceAsString()` − formated string of trace
 8050 | * `Exception::__toString` gives the string representation of the exception.
 8051 | 
 8052 | **Source:** _github.com/Bootsity_
 8053 | 
 8054 | #### Q33: Differentiate between parameterised and non parameterised functions ⭐⭐⭐
 8055 | **Answer:**
 8056 | - **Non parameterised functions** don't take any parameter at the time of calling.
 8057 | - **Parameterised functions** take one or more arguments while calling. These are used at run time of the program when output depends on dynamic values given at run time
 8058 | There are two ways to access the parameterised function:
 8059 |  1. _call by value_: (here we pass the value directly )
 8060 |  2. _call by reference_: (here we pass the address location where the value is stored)
 8061 | 
 8062 | **Source:** _github.com/Bootsity_
 8063 | 
 8064 | #### Q34: Explain function call by reference ⭐⭐⭐
 8065 | **Answer:**
 8066 | In case of call by reference, actual value is modified if it is modified inside the function. In such case, we need to use `&` symbol with formal arguments. The `&` represents reference of the variable.
 8067 | 
 8068 | Example:
 8069 | 
 8070 | ```php  
 8071 | function adder(&$str2) {  
 8072 |     $str2 .= 'Call By Reference';  
 8073 | }
 8074 | $str = 'This is ';  
 8075 | adder($str);  
 8076 | echo $str;  
 8077 | ```
 8078 | 
 8079 | Output:
 8080 | ```sh
 8081 | This is Call By Reference
 8082 | ```
 8083 | 
 8084 | **Source:** _github.com/Bootsity_
 8085 | 
 8086 | #### Q35: Why do we use extract()? ⭐⭐⭐
 8087 | **Answer:**
 8088 | The `extract()` function imports variables into the local symbol table from an array.
 8089 | This function uses array keys as variable names and values as variable values. For each element it will create a variable in the current symbol table.
 8090 | This function returns the number of variables extracted on success.
 8091 | 
 8092 | Example:
 8093 | 
 8094 | ```php
 8095 | $a = "Original";
 8096 | $my_array = array("a" => "Cat","b" => "Dog", "c" => "Horse");
 8097 | extract($my_array);
 8098 | echo "\$a = $a; \$b = $b; \$c = $c";
 8099 | ```
 8100 | 
 8101 | Output:
 8102 | 
 8103 | ```sh
 8104 | $a = Cat; $b = Dog; $c = Horse
 8105 | ```
 8106 | 
 8107 | **Source:** _github.com/Bootsity_
 8108 | 
 8109 | #### Q36: explain what is a closure in PHP and why does it use the “use” identifier? ⭐⭐⭐⭐
 8110 | **Details:**
 8111 | Consider this code:
 8112 | ```php
 8113 | public function getTotal($tax)
 8114 | {
 8115 |     $total = 0.00;
 8116 | 
 8117 |     $callback =
 8118 |         function ($quantity, $product) use ($tax, &$total)
 8119 |         {
 8120 |             $pricePerItem = constant(__CLASS__ . "::PRICE_" .
 8121 |                 strtoupper($product));
 8122 |             $total += ($pricePerItem * $quantity) * ($tax + 1.0);
 8123 |         };
 8124 | 
 8125 |     array_walk($this->products, $callback);
 8126 |     return round($total, 2);
 8127 | }
 8128 | ```
 8129 | Could you explain why use it?
 8130 | 
 8131 | **Answer:**
 8132 | Read Full Answer on 👉 <a href='https://www.fullstack.cafe\blog\php-interview-questions'>FullStack.Cafe</a>
 8133 | 
 8134 | #### Q37: What exactly are late static bindings in PHP? ⭐⭐⭐⭐
 8135 | **Answer:**
 8136 | Read Full Answer on 👉 <a href='https://www.fullstack.cafe\blog\php-interview-questions'>FullStack.Cafe</a>
 8137 | 
 8138 | #### Q38: How to measure execution times of PHP scripts? ⭐⭐⭐⭐
 8139 | **Details:**
 8140 | I want to know how many milliseconds a PHP while-loop takes to execute. Could you help me?
 8141 | 
 8142 | **Answer:**
 8143 | Read Full Answer on 👉 <a href='https://www.fullstack.cafe\blog\php-interview-questions'>FullStack.Cafe</a>
 8144 | 
 8145 | #### Q39: What is the best method to merge two PHP objects? ⭐⭐⭐⭐
 8146 | **Details:**
 8147 | ```php
 8148 | //We have this:
 8149 | $objectA->a;
 8150 | $objectA->b;
 8151 | $objectB->c;
 8152 | $objectB->d;
 8153 | 
 8154 | //We want the easiest way to get:
 8155 | $objectC->a;
 8156 | $objectC->b;
 8157 | $objectC->c;
 8158 | $objectC->d;
 8159 | ```
 8160 | 
 8161 | **Answer:**
 8162 | Read Full Answer on 👉 <a href='https://www.fullstack.cafe\blog\php-interview-questions'>FullStack.Cafe</a>
 8163 | 
 8164 | #### Q40: Compare mysqli or PDO - what are the pros and cons? ⭐⭐⭐⭐
 8165 | **Answer:**
 8166 | Read Full Answer on 👉 <a href='https://www.fullstack.cafe\blog\php-interview-questions'>FullStack.Cafe</a>
 8167 | 
 8168 | #### Q41: What is use of Spaceship Operator? ⭐⭐⭐⭐
 8169 | **Answer:**
 8170 | Read Full Answer on 👉 <a href='https://www.fullstack.cafe\blog\php-interview-questions'>FullStack.Cafe</a>
 8171 | 
 8172 | #### Q42: Does PHP have threading? ⭐⭐⭐⭐
 8173 | **Answer:**
 8174 | Read Full Answer on 👉 <a href='https://www.fullstack.cafe\blog\php-interview-questions'>FullStack.Cafe</a>
 8175 | 
 8176 | #### Q43: Is PHP single or multi threaded? ⭐⭐⭐⭐
 8177 | **Answer:**
 8178 | Read Full Answer on 👉 <a href='https://www.fullstack.cafe\blog\php-interview-questions'>FullStack.Cafe</a>
 8179 | 
 8180 | #### Q44: Provide some ways to mimic multiple constructors in PHP ⭐⭐⭐⭐⭐
 8181 | **Details:**
 8182 | It's known you can't put two __construct functions with unique argument signatures in a PHP class but I'd like to do something like this:
 8183 | 
 8184 | ```php
 8185 | class Student 
 8186 | {
 8187 |    protected $id;
 8188 |    protected $name;
 8189 |    // etc.
 8190 | 
 8191 |    public function __construct($id){
 8192 |        $this->id = $id;
 8193 |       // other members are still uninitialised
 8194 |    }
 8195 | 
 8196 |    public function __construct($row_from_database){
 8197 |        $this->id = $row_from_database->id;
 8198 |        $this->name = $row_from_database->name;
 8199 |        // etc.
 8200 |    }
 8201 | }
 8202 | ```
 8203 | What is the best way to achieve this in PHP?
 8204 | 
 8205 | **Answer:**
 8206 | Read Full Answer on 👉 <a href='https://www.fullstack.cafe\blog\php-interview-questions'>FullStack.Cafe</a>
 8207 | 
 8208 | #### Q45: How could we implement method overloading in PHP? ⭐⭐⭐⭐⭐
 8209 | **Answer:**
 8210 | Read Full Answer on 👉 <a href='https://www.fullstack.cafe\blog\php-interview-questions'>FullStack.Cafe</a>
 8211 | 
 8212 | ## [[⬆]](#toc) <a name=5SalaryNegotiationRulesforSoftwareDevelopers>5 Salary Negotiation Rules for Software Developers</a>
 8213 | > Originally published on 👉 <a href='https://www.fullstack.cafe\blog\5-salary-negotiation-rules-for-software-developers'>5 Salary Negotiation Rules for Software Developers | FullStack.Cafe</a>
 8214 | 
 8215 | #### Q1: career test ⭐⭐⭐
 8216 | **Details:**
 8217 | test
 8218 | 
 8219 | **Answer:**
 8220 | test
 8221 | 
 8222 | ## [[⬆]](#toc) <a name=50CommonFrontEndDeveloperInterviewQuestions[2019Edition]>50 Common Front End Developer Interview Questions [2019 Edition]</a>
 8223 | > Originally published on 👉 <a href='https://www.fullstack.cafe\blog\front-end-developer-interview-questions'>50 Common Front End Developer Interview Questions [2019 Edition] | FullStack.Cafe</a>
 8224 | 
 8225 | #### Q1: Explain the CSS “box model” and the layout components that it consists of ⭐⭐
 8226 | **Answer:**
 8227 | The CSS box model is a rectangular layout paradigm for HTML elements that consists of the following:
 8228 | 
 8229 | * **Content** - The content of the box, where text and images appear
 8230 | * **Padding** - A transparent area surrounding the content (i.e., the amount of space between the border and the content)
 8231 | * **Border** - A border surrounding the padding (if any) and content
 8232 | * **Margin** - A transparent area surrounding the border (i.e., the amount of space between the border and any neighboring elements)
 8233 | 
 8234 | **Source:** _toptal.com_
 8235 | 
 8236 | #### Q2: What is a CSS rule? ⭐⭐
 8237 | **Answer:**
 8238 | Web browsers apply **CSS rules** to a document to affect how they are displayed. A CSS rule is formed from:
 8239 | 
 8240 | * A **set of properties**, which have values set to update how the HTML content is displayed,
 8241 | * A **selector**, which selects the element(s) you want to apply the updated property values to.
 8242 | 
 8243 | A set of CSS rules contained within a stylesheet determines how a webpage should look. 
 8244 | 
 8245 | **Source:** _developer.mozilla.org_
 8246 | 
 8247 | #### Q3: What is Sass? ⭐⭐
 8248 | **Answer:**
 8249 | **Sass** or **Syntactically Awesome StyleSheets** is a *CSS* preprocessor that adds power and elegance to the basic language. It allows you to use variables, nested rules, mixins, inline imports, and more, all with a fully CSS-compatible syntax. Sass helps keep large stylesheets well-organized, and get small stylesheets up and running quickly.
 8250 | 
 8251 | A *CSS preprocessor* is a scripting language that extends CSS by allowing developers to write code in one language and then compile it into CSS. 
 8252 | 
 8253 | 
 8254 | **Source:** _sass-lang.com_
 8255 | 
 8256 | #### Q4: What is a Mixin and how to use on? ⭐⭐⭐
 8257 | **Answer:**
 8258 | A **Mixin** is a block of code that lets us group CSS declarations we may reuse throughout our site.
 8259 | 
 8260 | To define mixin:
 8261 | ```css
 8262 | @mixin grid($flex: true /*default argument*/) {
 8263 |     @if $flex {
 8264 |         @include flex;
 8265 |     } @else {
 8266 |         display: block;
 8267 |     }
 8268 | }
 8269 | ```
 8270 | 
 8271 | To use a Mixin, we simply use `@include` followed by the name of the Mixin and a semi-colon.
 8272 | ```css
 8273 | /*scss*/
 8274 | .row {
 8275 |     @include grid(true);
 8276 | }
 8277 | 
 8278 | /*css*/
 8279 | .row {
 8280 |     display: -webkit-flex;
 8281 |     display: flex;
 8282 | }
 8283 | ```
 8284 | 
 8285 | **Source:** _scotch.io_
 8286 | 
 8287 | #### Q5: What’s the difference between “resetting” and “normalizing” CSS? Which would you choose, and why? ⭐⭐⭐
 8288 | **Answer:**
 8289 | * **Resetting** — is meant to strip all default browser styling on elements. For e.g. `margins`, `paddings`, `font-sizes` of all elements are reset to be the same. You will have to redeclare styling for common typographic elements.
 8290 | * **Normalizing** — preserves useful default styles rather than “unstyling” everything. It also corrects bugs for common browser dependencies.
 8291 | 
 8292 | It's a good idea to choose resetting when you have very a customized or unconventional site design such that I need to do a lot of my own styling do not need any default styling to be preserved.
 8293 | 
 8294 | 
 8295 | **Source:** _codeburst.io_
 8296 | 
 8297 | #### Q6: What is a Grid System in CSS? ⭐⭐⭐
 8298 | **Answer:**
 8299 | A grid system is a structure that allows for content to be stacked both vertically and horizontally in a consistent and easily manageable fashion. Grid systems include two key components: rows and columns.
 8300 | 
 8301 | Some Grid Systems:
 8302 | * Simple Grid
 8303 | * Pure
 8304 | * Flexbox Grid
 8305 | * Bootstrap
 8306 | * Foundation
 8307 | 
 8308 | **Source:** _sitepoint.com_
 8309 | 
 8310 | #### Q7: Explain meta tags in HTML ⭐
 8311 | **Answer:**
 8312 | - **Meta tags** always go inside **head tag** of the HTML page
 8313 | - **Meta tags** is always passed as name/value pairs
 8314 | - **Meta tags** are not displayed on the page but intended for the browser
 8315 | - **Meta tags** can contain information about **character encoding**, **description**, **title** of the document etc,
 8316 | 
 8317 | **Example**:
 8318 | 
 8319 | ```html
 8320 | <!DOCTYPE html>
 8321 | <html>
 8322 | <head>
 8323 |   <meta name="description" content="I am a web page with description"> 
 8324 |   <title>Home Page</title>
 8325 | </head>
 8326 | <body>
 8327 |   
 8328 | </body>
 8329 | </html>
 8330 | ```
 8331 | 
 8332 | 
 8333 | **Source:** _github.com/FuelFrontend_
 8334 | 
 8335 | #### Q8: What is the difference between span and div? ⭐⭐
 8336 | **Answer:**
 8337 | * `div` is a block element
 8338 | * `span` is inline element 
 8339 | 
 8340 | For bonus points, you could point out that it’s illegal to place a block element inside an inline element, and that while `div` can have a `p` tag, and a `p` tag can have a `span`, it is not possible for `span` to have a `div` or `p` tag inside.
 8341 | 
 8342 | **Source:** _thatjsdude.com_
 8343 | 
 8344 | #### Q9: What are `defer` and `async` attributes on a `<script>` tag? ⭐⭐⭐
 8345 | **Answer:**
 8346 | If neither attribute is present, the script is downloaded and executed synchronously, and will halt parsing of the document until it has finished executing (default behavior). Scripts are downloaded and executed in the order
 8347 | they are encountered.
 8348 | 
 8349 | The `defer` attribute downloads the script while the document is still parsing but waits until the document has finished parsing before executing it, equivalent to executing inside a `DOMContentLoaded` event listener. `defer` scripts will execute in order.
 8350 | 
 8351 | The `async` attribute downloads the script during parsing the document but will pause the parser to execute the script before it has fully finished parsing. `async` scripts will not necessarily execute in order.
 8352 | 
 8353 | Note: both attributes must only be used if the script has a `src` attribute (i.e. not an inline script).
 8354 | 
 8355 | ```html
 8356 | <script src="myscript.js"></script>
 8357 | <script src="myscript.js" defer></script>
 8358 | <script src="myscript.js" async></script>
 8359 | ```
 8360 | 
 8361 | **Source:** _growingwiththeweb.com_
 8362 | 
 8363 | #### Q10: What's new in HTML 5? ⭐⭐⭐
 8364 | **Answer:**
 8365 | HTML 5 adds a lot of new features to the HTML specification
 8366 | 
 8367 | **New Doctype**
 8368 | 
 8369 | Still using that pesky, impossible-to-memorize XHTML doctype?
 8370 | 
 8371 | ```html
 8372 | <!DOCTYPE html PUBLIC "-//W3C//DTD XHTML 1.0 Transitional//EN"
 8373 |     "http://www.w3.org/TR/xhtml1/DTD/xhtml1-transitional.dtd">
 8374 | ```
 8375 | 
 8376 | If so, why? Switch to the new HTML5 doctype. You'll live longer -- as Douglas Quaid might say.
 8377 | 
 8378 | ```html
 8379 | <!DOCTYPE html>
 8380 | ```
 8381 | 
 8382 | **New Structure**
 8383 | 
 8384 | - `<section>` - to define sections of pages
 8385 | - `<header>` - defines the header of a page
 8386 | - `<footer>` - defines the footer of a page
 8387 | - `<nav>` - defines the navigation on a page
 8388 | - `<article>` - defines the article or primary content on a page
 8389 | - `<aside>` - defines extra content like a sidebar on a page
 8390 | - `<figure>` - defines images that annotate an article
 8391 | 
 8392 | **New Inline Elements**
 8393 | 
 8394 | These inline elements define some basic concepts and keep them semantically marked up, mostly to do with time:
 8395 | 
 8396 | - `<mark>` - to indicate content that is marked in some fashion
 8397 | - `<time>` - to indicate content that is a time or date
 8398 | - `<meter>` - to indicate content that is a fraction of a known range - such as disk usage
 8399 | - `<progress>` - to indicate the progress of a task towards completion
 8400 | 
 8401 | **New Form Types**
 8402 | 
 8403 | - `<input type="datetime">`
 8404 | - `<input type="datetime-local">`
 8405 | - `<input type="date">`
 8406 | - `<input type="month">`
 8407 | - `<input type="week">`
 8408 | - `<input type="time">`
 8409 | - `<input type="number">`
 8410 | - `<input type="range">`
 8411 | - `<input type="email">`
 8412 | - `<input type="url">`
 8413 | 
 8414 | **New Elements**
 8415 | 
 8416 | There are a few exciting new elements in HTML 5:
 8417 | 
 8418 | - `<canvas>` - an element to give you a drawing space in JavaScript on your Web pages. It can let you add images or graphs to tool tips or just create dynamic graphs on your Web pages, built on the fly.
 8419 | - `<video>` - add video to your Web pages with this simple tag.
 8420 | - `<audio>` - add sound to your Web pages with this simple tag.
 8421 | 
 8422 | **No More Types for Scripts and Links**
 8423 | 
 8424 | You possibly still add the `type` attribute to your `link` and `script` tags.
 8425 | 
 8426 | ```html
 8427 | <link rel="stylesheet" href="path/to/stylesheet.css" type="text/css" />
 8428 | <script type="text/javascript" src="path/to/script.js"></script>
 8429 | ```
 8430 | 
 8431 | This is no longer necessary. It's implied that both of these tags refer to stylesheets and scripts, respectively. As such, we can remove the `type` attribute all together.
 8432 | 
 8433 | ```html
 8434 | <link rel="stylesheet" href="path/to/stylesheet.css" />
 8435 | <script src="path/to/script.js"></script>
 8436 | ```
 8437 | 
 8438 | **Make your content editable**
 8439 | 
 8440 | The new browsers have a nifty new attribute that can be applied to elements, called `contenteditable`. As the name implies, this allows the user to edit any of the text contained within the element, including its children. There are a variety of uses for something like this, including an app as simple as a to-do list, which also takes advantage of local storage.
 8441 | 
 8442 | ```html
 8443 | <h2> To-Do List </h2>
 8444 | <ul contenteditable="true">
 8445 |   <li> Break mechanical cab driver. </li>
 8446 |   <li> Drive to abandoned factory
 8447 |   <li> Watch video of self </li>
 8448 | </ul>
 8449 | ```
 8450 | 
 8451 | **Attributes**
 8452 | 
 8453 | - `require` to mention the form field is required
 8454 | - `autofocus` puts the cursor on the input field
 8455 | 
 8456 | **Source:** _github.com/FuelFrontend_
 8457 | 
 8458 | #### Q11: What is Coercion in JavaScript? 
 8459 | **Answer:**
 8460 | In JavaScript conversion between different two build-in types called `coercion`.  Coercion comes in two forms in JavaScript: *explicit* and *implicit*.
 8461 | 
 8462 | Here's an example of explicit coercion:
 8463 | ```js
 8464 | var a = "42";
 8465 | 
 8466 | var b = Number( a );
 8467 | 
 8468 | a;				// "42"
 8469 | b;				// 42 -- the number!
 8470 | ```
 8471 | And here's an example of implicit coercion:
 8472 | ```js
 8473 | var a = "42";
 8474 | 
 8475 | var b = a * 1;	// "42" implicitly coerced to 42 here
 8476 | 
 8477 | a;				// "42"
 8478 | b;				// 42 -- the number!
 8479 | ``` 
 8480 | 
 8481 | #### Q12: What is Scope in JavaScript? ⭐
 8482 | **Answer:**
 8483 | In JavaScript, each function gets its own *scope*. Scope is basically a collection of variables as well as the rules for how those variables are accessed by name. Only code inside that function can access that function's scoped variables.
 8484 | 
 8485 | A variable name has to be unique within the same scope. A scope can be nested inside another scope. If one scope is nested inside another, code inside the innermost scope can access variables from either scope.
 8486 | 
 8487 | #### Q13: What is strict mode? ⭐⭐
 8488 | **Answer:**
 8489 | *Strict Mode* is a new feature in ECMAScript 5 that allows you to place a program, or a function, in a "strict" operating context. This strict context prevents certain actions from being taken and throws more exceptions.
 8490 | 
 8491 | ```js
 8492 | // Non-strict code...
 8493 | 
 8494 | (function(){
 8495 |   "use strict";
 8496 | 
 8497 |   // Define your library strictly...
 8498 | })();
 8499 | 
 8500 | // Non-strict code...
 8501 | ```
 8502 | 
 8503 | #### Q14: What is IIFEs (Immediately Invoked Function Expressions)? ⭐⭐⭐
 8504 | **Answer:**
 8505 | It’s an Immediately-Invoked Function Expression, or IIFE for short. It executes immediately after it’s created:
 8506 | ```js
 8507 | (function IIFE(){
 8508 | 	console.log( "Hello!" );
 8509 | })();
 8510 | // "Hello!"
 8511 | ```
 8512 | 
 8513 | This pattern is often used when trying to avoid polluting the global namespace, because all the variables used inside the IIFE (like in any other normal function) are not visible outside its scope.
 8514 | 
 8515 | **Source:** _stackoverflow.com_
 8516 | 
 8517 | #### Q15: What is “closure” in javascript? Provide an example? ⭐⭐⭐⭐
 8518 | **Answer:**
 8519 | Read Full Answer on 👉 <a href='https://www.fullstack.cafe\blog\front-end-developer-interview-questions'>FullStack.Cafe</a>
 8520 | 
 8521 | #### Q16: Explain the Prototype Design Pattern ⭐⭐⭐⭐
 8522 | **Answer:**
 8523 | Read Full Answer on 👉 <a href='https://www.fullstack.cafe\blog\front-end-developer-interview-questions'>FullStack.Cafe</a>
 8524 | 
 8525 | #### Q17: Compare SQL databases and MongoDB at a high level. ⭐⭐
 8526 | **Answer:**
 8527 | SQL databases store data in form of tables, rows, columns and records. This data is stored in a pre-defined data model which is not very much flexible for today's real-world highly growing applications. MongoDB in contrast uses a flexible structure which can be easily modified and extended.
 8528 | 
 8529 | **Source:** _tutorialspoint.com_
 8530 | 
 8531 | #### Q18: What is Node.js? ⭐
 8532 | **Answer:**
 8533 | Node.js is a web application framework built on Google Chrome's JavaScript Engine (V8 Engine).
 8534 | 
 8535 | Node.js comes with runtime environment on which a Javascript based script can be interpreted and executed (It is analogus to JVM to JAVA byte code). This runtime allows to execute a JavaScript code on any machine outside a browser. Because of this runtime of Node.js, JavaScript is now can be executed on server as well.
 8536 | 
 8537 | *Node.js = Runtime Environment + JavaScript Library*
 8538 | 
 8539 | **Source:** _tutorialspoint.com_
 8540 | 
 8541 | #### Q19: What is npm? ⭐
 8542 | **Answer:**
 8543 | `npm` stands for Node Package Manager. npm provides following two main functionalities:
 8544 | 
 8545 | *   Online repositories for node.js packages/modules which are searchable on [search.nodejs.org](http://search.nodejs.org)
 8546 | *   Command line utility to install packages, do version management and dependency management of Node.js packages.
 8547 | 
 8548 | **Source:** _tutorialspoint.com_
 8549 | 
 8550 | #### Q20: If Node.js is single threaded then how it handles concurrency? ⭐⭐
 8551 | **Answer:**
 8552 | Node provides a single thread to programmers so that code can be written easily and without bottleneck. Node internally uses multiple POSIX threads for various I/O operations such as File, DNS, Network calls etc.
 8553 | 
 8554 | When Node gets I/O request it creates or uses a thread to perform that I/O operation and once the operation is done, it pushes the result to the event queue. On each such event, event loop runs and checks the queue and if the execution stack of Node is empty then it adds the queue result to execution stack.
 8555 | 
 8556 | This is how Node manages concurrency.
 8557 | 
 8558 | **Source:** _codeforgeek.com_
 8559 | 
 8560 | #### Q21: What is Callback Hell? ⭐⭐
 8561 | **Answer:**
 8562 | The asynchronous function requires callbacks as a return parameter. When multiple asynchronous functions are chained together then callback hell situation comes up. 
 8563 | 
 8564 | **Source:** _codeforgeek.com_
 8565 | 
 8566 | #### Q22: How can you avoid callback hells? ⭐⭐⭐
 8567 | **Answer:**
 8568 | To do so you have more options:
 8569 | 
 8570 | *   **modularization**: break callbacks into independent functions
 8571 | *   use _Promises_
 8572 | *   use `yield` with _Generators_ and/or _Promises_
 8573 | 
 8574 | **Source:** _tutorialspoint.com_
 8575 | 
 8576 | #### Q23: How would you scale Node application? ⭐⭐⭐⭐⭐
 8577 | **Answer:**
 8578 | Read Full Answer on 👉 <a href='https://www.fullstack.cafe\blog\front-end-developer-interview-questions'>FullStack.Cafe</a>
 8579 | 
 8580 | #### Q24: What is encapsulation? ⭐⭐
 8581 | **Answer:**
 8582 | **Encapsulation** is defined _as the process of enclosing one or more items within a physical or logical package_. Encapsulation, in object oriented programming methodology, prevents access to implementation details.
 8583 | 
 8584 | **Source:** _tutorialspoint.com_
 8585 | 
 8586 | #### Q25: What is polymorphism? ⭐⭐
 8587 | **Answer:**
 8588 | The word polymorphism means having many forms. In object-oriented programming paradigm, polymorphism is often expressed as _one interface, multiple functions_.
 8589 | 
 8590 | 
 8591 | **Source:** _tutorialspoint.com_
 8592 | 
 8593 | #### Q26: What is ReactJS? ⭐
 8594 | **Answer:**
 8595 | ReactJS is an **open-source frontend JavaScript library** which is used for building user interfaces especifically for single page applications. It is used for handling view layer for web and mobile apps. React was created by Jordan Walke, a software engineer working for Facebook. ReactJS was first deployed on Facebook’s newsfeed in 2011 and on Instagram.com in 2012.
 8596 | 
 8597 | **Source:** _https://github.com/sudheerj_
 8598 | 
 8599 | #### Q27: What is the point of Redux? ⭐⭐
 8600 | **Answer:**
 8601 | Application state management that is easy to reason about, maintain and manage in an asynchronous web application environment.
 8602 | 
 8603 | **Source:** _github.com/WebPredict_
 8604 | 
 8605 | #### Q28: What is Flux? ⭐⭐
 8606 | **Answer:**
 8607 | Unidrectional application flow paradigm popular a few years back in React; mostly superceded by Redux these days.
 8608 | 
 8609 | **Source:** _github.com/WebPredict_
 8610 | 
 8611 | #### Q29: What are advantages of REST web services? ⭐⭐
 8612 | **Answer:**
 8613 | Some of the advantages of REST web services are:
 8614 | 
 8615 | * Learning curve is easy since it works on HTTP protocol
 8616 | * Supports multiple technologies for data transfer such as text, xml, json, image etc.
 8617 | * No contract defined between server and client, so loosely coupled implementation.
 8618 | * REST is a lightweight protocol
 8619 | * REST methods can be tested easily over browser.
 8620 | 
 8621 | **Source:** _journaldev.com_
 8622 | 
 8623 | #### Q30: Mention what is the difference between PUT and POST? ⭐⭐⭐
 8624 | **Answer:**
 8625 | *PUT* puts a file or resource at a particular URI and exactly at that URI.  If there is already a file or resource at that URI, PUT changes that file or resource.  If there is no resource or file there, PUT makes one
 8626 | 
 8627 | *POST* sends data to a particular URI and expects the resource at that URI to deal with the request.  The web server at this point can decide what to do with the data in the context of specified resource
 8628 | 
 8629 | *PUT is idempotent* meaning, invoking it any number of times will not have an impact on resources.
 8630 | 
 8631 | However, *POST is not idempotent*, meaning if you invoke POST multiple times it keeps creating more resources
 8632 | 
 8633 | **Source:** _career.guru99.com_
 8634 | 
 8635 | #### Q31: Name some best practices for better RESTful API design ⭐⭐⭐⭐⭐
 8636 | **Answer:**
 8637 | Read Full Answer on 👉 <a href='https://www.fullstack.cafe\blog\front-end-developer-interview-questions'>FullStack.Cafe</a>
 8638 | 
 8639 | #### Q32: What is meant by the KISS principle? ⭐⭐
 8640 | **Answer:**
 8641 | **KISS**, a backronym for "keep it simple, stupid", is a design principle noted by the U.S. Navy in 1960. The KISS principle states that most systems work best if they are kept simple rather than made complicated; therefore simplicity should be a key goal in design, and that unnecessary complexity should be avoided.
 8642 | 
 8643 | **Source:** _stackoverflow.com_
 8644 | 
 8645 | #### Q33: What Is Load Balancing? ⭐⭐⭐
 8646 | **Answer:**
 8647 | 
 8648 | **Load balancing** is simple technique for distributing workloads across multiple machines or clusters. The most common and simple load balancing algorithm is Round Robin. In this type of load balancing the request is divided in circular order ensuring all machines get equal number of requests and no single machine is overloaded or underloaded.  
 8649 |   
 8650 | **The Purpose of load balancing is to**  
 8651 |   
 8652 | *   Optimize resource usage (avoid overload and under-load of any machines)
 8653 | *   Achieve Maximum Throughput
 8654 | *   Minimize response time
 8655 | 
 8656 | **Most common load balancing techniques in web based applications are**  
 8657 | 
 8658 | 1.  Round robin
 8659 | 2.  Session affinity or sticky session
 8660 | 3.  IP Address affinity
 8661 | 
 8662 | 
 8663 | **Source:** _fromdev.com_
 8664 | 
 8665 | #### Q34: What does SOLID stand for? What are its principles? ⭐⭐⭐
 8666 | **Answer:**
 8667 | **S.O.L.I.D** is an acronym for the first five object-oriented design (OOD) principles by Robert C. Martin.
 8668 | 
 8669 | * **S** - *Single-responsiblity principle*. A class should have one and only one reason to change, meaning that a class should have only one job.
 8670 | * **O** - *Open-closed principle*. Objects or entities should be open for extension, but closed for modification.
 8671 | * **L** - *Liskov substitution principle*. Let q(x) be a property provable about objects of x of type T. Then q(y) should be provable for objects y of type S where S is a subtype of T.
 8672 | * **I** - *Interface segregation principle*. A client should never be forced to implement an interface that it doesn't use or clients shouldn't be forced to depend on methods they do not use.
 8673 | * **D** - *Dependency Inversion Principle*. Entities must depend on abstractions not on concretions. It states that the high level module must not depend on the low level module, but they should depend on abstractions.
 8674 | 
 8675 | **Source:** _scotch.io_
 8676 | 
 8677 | #### Q35: Are you familiar with The Twelve-Factor App principles? ⭐⭐⭐⭐⭐
 8678 | **Answer:**
 8679 | Read Full Answer on 👉 <a href='https://www.fullstack.cafe\blog\front-end-developer-interview-questions'>FullStack.Cafe</a>
 8680 | 
 8681 | #### Q36: Name some basic design elements ⭐
 8682 | **Answer:**
 8683 | The elements of design are:
 8684 | 
 8685 | * **LINE** – The linear marks made with a pen or brush or the edge created when two shapes meet.
 8686 | * **SHAPE** – A shape is a self contained defined area of geometric (squares and circles), or organic (free formed shapes or natural shapes). A positive shape automatically creates a negative shape.
 8687 | * **DIRECTION** – All lines have direction – Horizontal, Vertical or Oblique. Horizontal suggests calmness, stability and tranquillity. Vertical gives a feeling of balance, formality and alertness. Oblique suggests movement and action
 8688 | * **SIZE** – Size is simply the relationship of the area occupied by one shape to that of another.
 8689 | * **TEXTURE** – Texture is the surface quality of a shape – rough, smooth, soft hard glossy etc.
 8690 | * **COLOUR** – Colour is light reflected off objects. Color has three main characteristics: hue or its name (red, green, blue, etc.), value (how light or dark it is), and intensity (how bright or dull it is).
 8691 | 
 8692 | <div class="text-center">
 8693 | <img src="http://www.j6design.com.au/wp-content/uploads/2014/02/designelements-1024x640.jpg" class="img-fluid" style="max-width: 500px;"/>
 8694 | </div>
 8695 | 
 8696 | **Source:** _j6design.com.au_
 8697 | 
 8698 | #### Q37: What is User Centered Design? ⭐⭐
 8699 | **Answer:**
 8700 | **User-centered design** is an iterative design process in which designers focus on the users and their needs in each phase of the design process. UCD calls for involving users throughout the design process via a variety of research and design techniques so as to create highly usable and accessible products for them.
 8701 | 
 8702 | User-centered design demands that designers employ a mixture of *investigative* (e.g., surveys and interviews) and *generative* (e.g., brainstorming) methods and tools to develop an understanding of user needs.
 8703 | 
 8704 | **Source:** _interaction-design.org_
 8705 | 
 8706 | #### Q38: Name fundamental principles of design ⭐⭐⭐
 8707 | **Answer:**
 8708 | The fundamental principles of design are:
 8709 | * **BALANCE** — Balance in design is similar to balance in physics. A large shape close to the center can be balanced by a small shape close to the edge. Balance provides stability and structure to a design. It’s the weight distributed in the design by the placement of your elements.
 8710 | * **PROXIMITY** — Proximity creates a relationship between elements. It provides a focal point. Proximity doesn’t mean that elements have to be placed together, it means they should be visually connected in some way.
 8711 | * **ALIGNMENT** — Allows us to create order and organization. Aligning elements allows them to create a visual connection with each other.
 8712 | * **REPETITION** — Repetition strengthens a design by tying together individual elements. It helps to create association and consistency. Repetition can create rhythm (a feeling of organized movement).
 8713 | * **CONTRAST** — Contrast is the juxtaposition of opposing elements (opposite colors on the color wheel, or value light/dark, or direction — horizontal/vertical). Contrast allows us to emphasize or highlight key elements in your design.
 8714 | * **SPACE** — Space in art refers to the distance or area between, around, above, below, or within elements. Both positive and negative space are important factors to be considered in every design.
 8715 | 
 8716 | **Source:** _uxplanet.org_
 8717 | 
 8718 | #### Q39: What is SQL injection? ⭐
 8719 | **Answer:**
 8720 | Injection attacks stem from a lack of strict separation between program instructions (i.e., code) and user-provided (or external) input. This allows an attacker to inject malicious code into a data snippet. 
 8721 | 
 8722 | *SQL injection* is one of the most common types of injection attack. To carry it out, an attacker provides malicious SQL statements through the application. 
 8723 | 
 8724 | How to prevent:
 8725 | * **Prepared statements with parameterized queries**
 8726 | * **Stored procedures**
 8727 | * **Input validation** - blacklist validation and whitelist validation
 8728 | * **Principle of least privilege** - Application accounts shouldn’t assign DBA or admin type access onto the database server. This ensures that if an application is compromised, an attacker won’t have the rights to the database through the compromised application.
 8729 | 
 8730 | **Source:** _https://www.synopsys.com_
 8731 | 
 8732 | #### Q40: What is Cross-Site Scripting (XSS)? ⭐⭐
 8733 | **Answer:**
 8734 | Cross-Site Scripting (XSS) is an attack that occurs when an attacker uses a web application to send malicious code, generally in the form of a browser side script, to a different end user. 
 8735 | 
 8736 | The page provided by the server when someone requests it is unaltered. Instead, an XSS attack exploits a weakness in a page that include a variable submitted in a request to show up in raw form in the response. The page is only reflecting back what was submitted in that request. 
 8737 | 
 8738 | **Source:** _synopsys.com_
 8739 | 
 8740 | #### Q41: What is Content Security Policy? ⭐⭐
 8741 | **Answer:**
 8742 | **Content Security Policy (CSP)** is an HTTP header that allows site operators fine-grained control over where resources on their site can be loaded from. The use of this header is the best method to prevent cross-site scripting (XSS) vulnerabilities. Due to the difficulty in retrofitting CSP into existing websites, CSP is mandatory for all new websites and is strongly recommended for all existing high-risk sites.
 8743 | 
 8744 | The primary benefit of CSP comes from disabling the use of unsafe inline JavaScript. Inline JavaScript – either reflected or stored – means that improperly escaped user-inputs can generate code that is interpreted by the web browser as JavaScript. By using CSP to disable inline JavaScript, you can effectively eliminate almost all XSS attacks against your site.
 8745 | 
 8746 | **Source:** _infosec.mozilla.org_
 8747 | 
 8748 | #### Q42: What is ClickJacking? ⭐⭐⭐
 8749 | **Answer:**
 8750 | **ClickJacking** is an attack that fools users into thinking they are clicking on one thing when they are actually clicking on another. The attack is possible thanks to HTML frames (iframes). 
 8751 | 
 8752 | Its other name, user interface (UI) redressing, better describes what is going on. Users think they are using a web page’s normal UI, but in fact there is a hidden UI in control; in other words, the UI has been redressed. When users click something they think is safe, the hidden UI performs a different action.
 8753 | 
 8754 | **Source:** _synopsys.com_
 8755 | 
 8756 | #### Q43: What is webpack? ⭐
 8757 | **Answer:**
 8758 | **Webpack** is a build tool that puts all of your assets, including Javascript, images, fonts, and CSS, in a dependency graph. Webpack lets you use `require()` in your source code to point to local files, like images, and decide how they're processed in your final Javascript bundle, like replacing the path with a URL pointing to a CDN.
 8759 | 
 8760 | 
 8761 | 
 8762 | **Source:** _blog.andrewray.me_
 8763 | 
 8764 | #### Q44: Why and when should I Use Webpack? ⭐
 8765 | **Answer:**
 8766 | If you're building a complex Front End application with many **non-code static assets** such as CSS, images, fonts, etc, then yes, Webpack will give you great benefits.
 8767 | 
 8768 | If your application is fairly small, and you don't have many static assets and you only need to build one Javascript file to serve to the client, then Webpack might be more overhead than you need.
 8769 | 
 8770 | **Source:** _blog.andrewray.me_
 8771 | 
 8772 | #### Q45: Why do we use jQuery? ⭐⭐
 8773 | **Answer:**
 8774 | Due to following advantages.
 8775 | 
 8776 | *   Easy to use and learn.
 8777 | *   Easily expandable.
 8778 | *   Cross-browser support (IE 6.0+, FF 1.5+, Safari 2.0+, Opera 9.0+)
 8779 | *   Easy to use for DOM manipulation and traversal.
 8780 | *   Large pool of built in methods.
 8781 | *   AJAX Capabilities.
 8782 | *   Methods for changing or applying CSS, creating animations.
 8783 | *   Event detection and handling.
 8784 | *   Tons of plug-ins for all kind of needs.
 8785 | 
 8786 | **Source:** _codeproject.com_
 8787 | 
 8788 | #### Q46: How JavaScript and jQuery are different? ⭐⭐
 8789 | **Answer:**
 8790 | JavaScript is a language While jQuery is a library built in the JavaScript language that helps to use the JavaScript language.  
 8791 | 
 8792 | **Source:** _codeproject.com_
 8793 | 
 8794 | #### Q47: When would you use AngularJS vs jQuery? ⭐⭐⭐
 8795 | **Answer:**
 8796 | * **jQuery** - is a library used for DOM Manipulations - Has nothing to do with models - don't have two-way binding feature - becomes complex and difficult to maintain when size of project increases - Sometimes you have to write more code to achieve the same functionality as in Angular
 8797 | 
 8798 | * **Angular** - is a MVVM Framework - Used for creating SPA (Single Page Applications) - Has key features like routing, directives, two way data binding, models, dependency injection, unit tests etc - is modular - Maintainable, when project size increases - is Fast and many more.
 8799 | 
 8800 | Basically jQuery is a single tool (solves one specific problem: dom manipulation) where AngularJS is a whole toolbox with all kind of tools for different problems (routing, modelbindings, dom manipulation, etc.). Actually jqLite (subset of jQuery) is part of the AngularJS and you use it to solve the dom-manipulation thing.
 8801 | 
 8802 | **Source:** _stackoverflow.com_
 8803 | 
 8804 | ## [[⬆]](#toc) <a name=50CommonWebDeveloperInterviewQuestions[2020Updated]>50 Common Web Developer Interview Questions [2020 Updated]</a>
 8805 | > Originally published on 👉 <a href='https://www.fullstack.cafe\blog\web-developer-interview-questions'>50 Common Web Developer Interview Questions [2020 Updated] | FullStack.Cafe</a>
 8806 | 
 8807 | #### Q1: What is Sprint Planning? ⭐⭐
 8808 | **Answer:**
 8809 | The work to be performed in the Sprint is planned at the **Sprint Planning**. This plan is created by the collaborative work of the entire Scrum Team.
 8810 | 
 8811 | Sprint Planning answers the following:
 8812 | 
 8813 | * What can be delivered in the Increment resulting from the upcoming Sprint?
 8814 | * How will the work needed to deliver the Increment be achieved?
 8815 | 
 8816 | The Sprint Goal is an objective set for the Sprint that can be met through the implementation of Product Backlog. 
 8817 | 
 8818 | **Source:** _scrum.org_
 8819 | 
 8820 | #### Q2: What is test driven development? ⭐⭐
 8821 | **Answer:**
 8822 | **Test driven development (TDD)** is also known as test-driven design. In this method, developer first writes an automated test case which describes new function or improvement and then creates small codes to pass that test, and later re-factors the new code to meet the acceptable standards.
 8823 | 
 8824 | **Source:** _career.guru99.com_
 8825 | 
 8826 | #### Q3: What is blockchain? ⭐
 8827 | **Answer:**
 8828 | **Blockchain** is a secure distributed ledger (data structure or database) that maintains a continuously growing list of ordered records, called “blocks”,  that are linked using cryptography. Each block contains a cryptographic hash of the previous block, a timestamp, and transaction data.
 8829 | 
 8830 | By design, a blockchain is resistant to modification of the data. It is "an open, distributed ledger that can record transactions between two parties efficiently and in a verifiable and permanent way".
 8831 | 
 8832 | Once recorded, the data in any given block cannot be altered retroactively without alteration of all subsequent blocks, which requires consensus of the network majority. 
 8833 | 
 8834 | **Source:** _en.wikipedia.org_
 8835 | 
 8836 | #### Q4: What is DOM (Document Object Model) and how is it linked to CSS? ⭐⭐
 8837 | **Answer:**
 8838 | The *Document Object Model (DOM)* is a cross-platform and language-independent *application programming interface* that treats an HTML, XHTML, or XML document as a tree structure wherein each node is an object representing a part of the document. 
 8839 | 
 8840 | With the Document Object Model, programmers can create and build documents, navigate their structure, and add, modify, or delete elements and content. The DOM specifies interfaces which may be used to manage XML or HTML documents. 
 8841 | 
 8842 | When a browser displays a document, it must combine the document's content with its style information. The browser converts HTML and CSS into the DOM (Document Object Model). The DOM represents the document in the computer's memory. It combines the document's content with its style.
 8843 | 
 8844 | **Source:** _en.wikipedia.org_
 8845 | 
 8846 | #### Q5: What is CSS selectors? Name some. ⭐⭐⭐
 8847 | **Answer:**
 8848 | A CSS selector is the part of a CSS rule set that actually selects the content you want to style.
 8849 | 
 8850 | Consider some types of CSS selectors:
 8851 | * **Universal selector**: `*`
 8852 | * **Element type selector**: `ul`, `td`
 8853 | * **ID Selector**: `#id`
 8854 | * **Class selector**: `.box`
 8855 | * **Descendant combinator**: `#id .box`. The .box element doesn’t have to be an immediate child of #id.
 8856 | * **Child combinator**: `#id > .box`. Unlike the descendant combinator, there can’t be another element wrapping .box
 8857 | * **General Sibling Combinator**: `~`
 8858 | * **Adjacent Sibling Combinator**: `+`. The difference from general sibling combinaltor is that the targeted element must be an immediate sibling, not just a general sibling.
 8859 | * **Attribute Selector**: `input[type="text"]`
 8860 | * **Pseudo-class**: `a:hover`. A pseudo-class uses a colon character to identify a pseudo-state that an element might be in.
 8861 | * **Pseudo-element**: `.container::before`. This selector inserts an imaginary element into the page, inside the targeted element, before its contents.
 8862 | 
 8863 | 
 8864 | 
 8865 | 
 8866 | **Source:** _sitepoint.com_
 8867 | 
 8868 | #### Q6: How is responsive design different from adaptive design? ⭐⭐⭐
 8869 | **Answer:**
 8870 | Both *responsive* and *adaptive* design attempt to optimize the user experience across different devices, adjusting for different viewport sizes, resolutions, usage contexts, control mechanisms, and so on.
 8871 | 
 8872 | **Responsive design** works on the principle of flexibility — a single fluid website that can look good on any device. Responsive websites use *media queries*, *flexible grids*, and *responsive images* to create a user experience that flexes and changes based on a multitude of factors. Like a single ball growing or shrinking to fit through several different hoops.
 8873 | 
 8874 | **Adaptive design** is more like the modern definition of progressive enhancement. Instead of one flexible design, adaptive design detects the device and other features, and then provides the appropriate feature and layout based on a *predefined set of viewport sizes* and other characteristics. The site detects the type of device used, and delivers the pre-set layout for that device. Instead of a single ball going through several different-sized hoops, you’d have several different balls to use depending on the hoop size.
 8875 | 
 8876 | **Source:** _codeburst.io_
 8877 | 
 8878 | #### Q7: What is Design Patterns and why anyone should use them? ⭐
 8879 | **Answer:**
 8880 | Design patterns are a well-described solution to the most commonly encountered problems which occur during software development. 
 8881 | 
 8882 | Design pattern represents the best practices evolved over a period of time by experienced software developers. They promote reusability which leads to a more robust and maintainable code.
 8883 | 
 8884 | **Source:** _www.educba.com_
 8885 | 
 8886 | #### Q8: What is Adapter Pattern? ⭐⭐⭐
 8887 | **Answer:**
 8888 | *Adapter pattern* works as a bridge between two incompatible interfaces. This pattern involves a single class which is responsible to join functionalities of independent or incompatible interfaces (adaptees).
 8889 | 
 8890 | <div class="text-center"/>
 8891 | <img src="http://www.java2novice.com/images/ObjectAdapter.png" class="img-fluid" style="max-width: 500px" />
 8892 | </div>
 8893 | </br>
 8894 | A real life example could be a case of card reader which acts as an adapter between memory card and a laptop. You plugin the memory card into card reader and card reader into the laptop so that memory card can be read via laptop.
 8895 | 
 8896 | **Source:** _tutorialspoint.com_
 8897 | 
 8898 | #### Q9: What is meant by Continuous Integration? ⭐
 8899 | **Answer:**
 8900 | *Continuous Integration (CI)* is a development practice that requires developers to integrate code into a shared repository several times a day. Each check-in is then verified by an automated build, allowing teams to detect problems early. 
 8901 | 
 8902 | **Source:** _edureka.co_
 8903 | 
 8904 | #### Q10: What does Containerization mean? ⭐⭐
 8905 | **Answer:**
 8906 | *Containerisation* is a type of *virtualization* strategy that emerged as an alternative to traditional hypervisor-based virtualization. 
 8907 | 
 8908 | In containerization, the operating system is shared by the different containers rather than cloned for each virtual machine. For example Docker provides a container virtualization platform that serves as a good alternative to hypervisor-based arrangements.
 8909 | 
 8910 | **Source:** _linoxide.com_
 8911 | 
 8912 | #### Q11: What is the purpose of the alt attribute on images? ⭐
 8913 | **Answer:**
 8914 | The `alt` attribute provides alternative information for an image if a user cannot view it. The `alt` attribute should be used to describe any images except those which only serve a decorative purposes, in which case it should be left empty.
 8915 | 
 8916 | 
 8917 | **Source:** _developer.mozilla.org_
 8918 | 
 8919 | #### Q12: What is the difference between span and div? ⭐⭐
 8920 | **Answer:**
 8921 | * `div` is a block element
 8922 | * `span` is inline element 
 8923 | 
 8924 | For bonus points, you could point out that it’s illegal to place a block element inside an inline element, and that while `div` can have a `p` tag, and a `p` tag can have a `span`, it is not possible for `span` to have a `div` or `p` tag inside.
 8925 | 
 8926 | **Source:** _thatjsdude.com_
 8927 | 
 8928 | #### Q13: Explain almost standard, full standard and quirks mode ⭐⭐⭐
 8929 | **Answer:**
 8930 | There are now three modes used by the layout engines in web browsers: quirks mode, almost standards mode, and full standards mode. 
 8931 | * In **quirks mode**, layout emulates nonstandard behavior in Navigator 4 and Internet Explorer 5. This is essential in order to support websites that were built before the widespread adoption of web standards. 
 8932 | * In **full standards mode**, the behavior is (hopefully) the behavior described by the HTML and CSS specifications. 
 8933 | * In **almost standards mode**, there are only a very small number of quirks implemented.
 8934 | 
 8935 | For HTML documents, browsers use a `DOCTYPE` in the beginning of the document to decide whether to handle it in quirks mode or standards mode.
 8936 | 
 8937 | **Source:** _developer.mozilla.org_
 8938 | 
 8939 | #### Q14: What is HTML5 Web Storage? Explain `localStorage` and `sessionStorage`. ⭐⭐⭐
 8940 | **Answer:**
 8941 | With HTML5, web pages can store data locally within the user’s browser.
 8942 | The data is stored in name/value pairs, and a web page can only access data stored by itself.
 8943 | 
 8944 | **Differences between `localStorage` and `sessionStorage` regarding lifetime:**
 8945 | 
 8946 | * Data stored through `localStorage` is permanent: it does not expire and remains stored on the user’s computer until a web app deletes it or the user asks the browser to delete it.
 8947 | * `sessionStorage` has the same lifetime as the top-level window or browser tab in which the data got stored. When the tab is permanently closed, any data stored through `sessionStorage` is deleted.
 8948 | 
 8949 | **Differences between `localStorage` and `sessionStorage` regarding storage scope:**
 8950 | 
 8951 | Both forms of storage are scoped to the document origin so that documents with different origins will never share the stored objects.
 8952 | 
 8953 | * `sessionStorage` is also scoped on a per-window basis. Two browser tabs with documents from the same origin have separate `sessionStorage` data.
 8954 | * Unlike in `localStorage`, the same scripts from the same origin can't access each other's `sessionStorage` when opened in different tabs.
 8955 | 
 8956 | **Source:** _w3schools.com_
 8957 | 
 8958 | #### Q15: What is progressive rendering? ⭐⭐⭐⭐
 8959 | **Answer:**
 8960 | Read Full Answer on 👉 <a href='https://www.fullstack.cafe\blog\web-developer-interview-questions'>FullStack.Cafe</a>
 8961 | 
 8962 | #### Q16: What is Coercion in JavaScript? 
 8963 | **Answer:**
 8964 | In JavaScript conversion between different two build-in types called `coercion`.  Coercion comes in two forms in JavaScript: *explicit* and *implicit*.
 8965 | 
 8966 | Here's an example of explicit coercion:
 8967 | ```js
 8968 | var a = "42";
 8969 | 
 8970 | var b = Number( a );
 8971 | 
 8972 | a;				// "42"
 8973 | b;				// 42 -- the number!
 8974 | ```
 8975 | And here's an example of implicit coercion:
 8976 | ```js
 8977 | var a = "42";
 8978 | 
 8979 | var b = a * 1;	// "42" implicitly coerced to 42 here
 8980 | 
 8981 | a;				// "42"
 8982 | b;				// 42 -- the number!
 8983 | ``` 
 8984 | 
 8985 | #### Q17: What is Scope in JavaScript? ⭐
 8986 | **Answer:**
 8987 | In JavaScript, each function gets its own *scope*. Scope is basically a collection of variables as well as the rules for how those variables are accessed by name. Only code inside that function can access that function's scoped variables.
 8988 | 
 8989 | A variable name has to be unique within the same scope. A scope can be nested inside another scope. If one scope is nested inside another, code inside the innermost scope can access variables from either scope.
 8990 | 
 8991 | #### Q18: Explain equality in JavaScript ⭐
 8992 | **Answer:**
 8993 | JavaScript has both strict and type–converting comparisons: 
 8994 | * **Strict comparison (e.g., ===)** checks for value equality without allowing *coercion*
 8995 | * **Abstract comparison (e.g. ==)** checks for value equality with *coercion* allowed
 8996 | 
 8997 | ```js
 8998 | var a = "42";
 8999 | var b = 42;
 9000 | 
 9001 | a == b;			// true
 9002 | a === b;		// false
 9003 | ```
 9004 | Some simple equalityrules:
 9005 | * If either value (aka side) in a comparison could be the `true` or `false` value, avoid `==` and use `===`.
 9006 | * If either value in a comparison could be of these specific values (`0`, `""`, or `[]` -- empty array), avoid `==` and use `===`.
 9007 | * In all other cases, you're safe to use `==`. Not only is it safe, but in many cases it simplifies your code in a way that improves readability.
 9008 | 
 9009 | #### Q19: Explain Null and Undefined in JavaScript ⭐⭐
 9010 | **Answer:**
 9011 | JavaScript (and by extension TypeScript) has two bottom types: `null` and `undefined`. They are *intended* to mean different things:
 9012 | * Something hasn't been initialized : `undefined`.
 9013 | * Something is currently unavailable: `null`.
 9014 | 
 9015 | #### Q20: Implement enqueue and dequeue using only two stacks ⭐⭐
 9016 | **Answer:**
 9017 | *Enqueue* means to add an element, *dequeue* to remove an element.
 9018 | 
 9019 | ```js
 9020 | var inputStack = []; // First stack
 9021 | var outputStack = []; // Second stack
 9022 | 
 9023 | // For enqueue, just push the item into the first stack
 9024 | function enqueue(stackInput, item) {
 9025 |   return stackInput.push(item);
 9026 | }
 9027 | 
 9028 | function dequeue(stackInput, stackOutput) {
 9029 |   // Reverse the stack such that the first element of the output stack is the
 9030 |   // last element of the input stack. After that, pop the top of the output to
 9031 |   // get the first element that was ever pushed into the input stack
 9032 |   if (stackOutput.length <= 0) {
 9033 |     while(stackInput.length > 0) {
 9034 |       var elementToOutput = stackInput.pop();
 9035 |       stackOutput.push(elementToOutput);
 9036 |     }
 9037 |   }
 9038 | 
 9039 |   return stackOutput.pop();
 9040 | }
 9041 | ```
 9042 | 
 9043 | **Source:** _https://github.com/kennymkchan_
 9044 | 
 9045 | #### Q21: What does "use strict" do? ⭐⭐
 9046 | **Answer:**
 9047 | The `use strict` literal is entered at the top of a JavaScript program or at the top of a function and it helps you write safer JavaScript code by throwing an error if a global variable is created by mistake. For example, the following program will throw an error:
 9048 | 
 9049 | ```js
 9050 | function doSomething(val) {
 9051 |   "use strict"; 
 9052 |   x = val + 10;
 9053 | }`
 9054 | ```
 9055 | 
 9056 | It will throw an error because `x` was not defined and it is being set to some value in the global scope, which isn't allowed with `use strict` The small change below fixes the error being thrown:
 9057 | 
 9058 | ```js
 9059 | function doSomething(val) {
 9060 |   "use strict"; 
 9061 |   var x = val + 10;
 9062 | }
 9063 | ```
 9064 | 
 9065 | **Source:** _coderbyte.com_
 9066 | 
 9067 | #### Q22: How to compare two objects in JavaScript? ⭐⭐⭐
 9068 | **Answer:**
 9069 | Two non-primitive values, like objects (including function and array) held by reference, so both `==` and `===` comparisons will simply check whether the references match, not anything about the underlying values.
 9070 | 
 9071 | For example, `arrays` are by default coerced to strings by simply joining all the values with commas (`,`) in between. So two arrays with the same contents would not be `==` equal:
 9072 | 
 9073 | ```js
 9074 | var a = [1,2,3];
 9075 | var b = [1,2,3];
 9076 | var c = "1,2,3";
 9077 | 
 9078 | a == c;		// true
 9079 | b == c;		// true
 9080 | a == b;		// false
 9081 | ```
 9082 | For *deep object comparison* use external libs like `deep-equal` or implement your own recursive equality algorithm.
 9083 | 
 9084 | 
 9085 | #### Q23: Could you explain the difference between ES5 and ES6 ⭐⭐⭐
 9086 | **Answer:**
 9087 | * **ECMAScript 5 (ES5)**: The 5th edition of ECMAScript, standardized in 2009. This standard has been implemented fairly completely in all modern browsers
 9088 | 
 9089 | * **ECMAScript 6 (ES6)/ ECMAScript 2015 (ES2015)**: The 6th edition of ECMAScript, standardized in 2015. This standard has been partially implemented in most modern browsers.
 9090 | 
 9091 | Here are some key differences between ES5 and ES6:
 9092 | * **Arrow functions** & **string interpolation**:<br/>
 9093 | Consider:
 9094 | ```js
 9095 | const greetings = (name) => {
 9096 |       return `hello ${name}`;
 9097 | }
 9098 | ```
 9099 | and even:
 9100 | ```js
 9101 | const greetings = name => `hello ${name}`;
 9102 | ```
 9103 | * **Const**. <br>
 9104 | Const works like a constant in other languages in many ways but there are some caveats. Const stands for ‘constant reference’ to a value. So with const, you can actually mutate the properties of an object being referenced by the variable. You just can’t change the reference itself.
 9105 | ```js
 9106 | const NAMES = [];
 9107 | NAMES.push("Jim");
 9108 | console.log(NAMES.length === 1); // true
 9109 | NAMES = ["Steve", "John"]; // error
 9110 | ```
 9111 | * **Block-scoped variables**.<br>
 9112 | The new ES6 keyword `let` allows developers to scope variables at the block level.
 9113 | `Let` doesn’t hoist in the same way `var` does.
 9114 | * **Default parameter values**
 9115 | Default parameters allow us to initialize functions with default values. A default is used when an argument is either omitted or undefined — meaning null is a valid value.
 9116 | ```js
 9117 | // Basic syntax
 9118 | function multiply (a, b = 2) {
 9119 |      return a * b;
 9120 | }
 9121 | multiply(5); // 10
 9122 | ```
 9123 | * ** Class Definition and Inheritance**<br>
 9124 | ES6 introduces language support for classes (`class` keyword), constructors (`constructor` keyword), and the `extend` keyword for inheritance.
 9125 | 
 9126 | * **for-of operator**<br>
 9127 | The for...of statement creates a loop iterating over iterable objects.
 9128 | * **Spread Operator**
 9129 | For objects merging
 9130 | ```js
 9131 | const obj1 = { a: 1, b: 2 }
 9132 | const obj2 = { a: 2, c: 3, d: 4}
 9133 | const obj3 = {...obj1, ...obj2}
 9134 | ```
 9135 | * **Promises**<br>
 9136 | Promises provide a mechanism to handle the results and errors from asynchronous operations.  You can accomplish the same thing with callbacks, but promises provide improved readability via method chaining and succinct error handling. 
 9137 | ```js
 9138 | const isGreater = (a, b) => {
 9139 |   return new Promise ((resolve, reject) => {
 9140 |     if(a > b) {
 9141 |       resolve(true)
 9142 |     } else {
 9143 |       reject(false)
 9144 |     }
 9145 |     })
 9146 | }
 9147 | isGreater(1, 2)
 9148 |   .then(result => {
 9149 |     console.log('greater')
 9150 |   })
 9151 |  .catch(result => {
 9152 |     console.log('smaller')
 9153 |  })
 9154 | ```
 9155 | * **Modules exporting & importing**
 9156 | Consider module exporting:
 9157 | ```js
 9158 | const myModule = { x: 1, y: () => { console.log('This is ES5') }}
 9159 | export default myModule;
 9160 | ```
 9161 | and importing:
 9162 | ```js
 9163 | import myModule from './myModule';
 9164 | ```
 9165 | 
 9166 | 
 9167 | #### Q24: Given two strings, return true if they are anagrams of one another ⭐⭐⭐
 9168 | **Details:**
 9169 | For example: `Mary` is an anagram of `Army`
 9170 | 
 9171 | **Answer:**
 9172 | ```js
 9173 | var firstWord = "Mary";
 9174 | var secondWord = "Army";
 9175 | 
 9176 | isAnagram(firstWord, secondWord); // true
 9177 | 
 9178 | function isAnagram(first, second) {
 9179 |   // For case insensitivity, change both words to lowercase.
 9180 |   var a = first.toLowerCase();
 9181 |   var b = second.toLowerCase();
 9182 | 
 9183 |   // Sort the strings, and join the resulting array to a string. Compare the results
 9184 |   a = a.split("").sort().join("");
 9185 |   b = b.split("").sort().join("");
 9186 | 
 9187 |   return a === b;
 9188 | }
 9189 | ```
 9190 | 
 9191 | **Source:** _https://github.com/kennymkchan_
 9192 | 
 9193 | #### Q25: What is IIFEs (Immediately Invoked Function Expressions)? ⭐⭐⭐
 9194 | **Answer:**
 9195 | It’s an Immediately-Invoked Function Expression, or IIFE for short. It executes immediately after it’s created:
 9196 | ```js
 9197 | (function IIFE(){
 9198 | 	console.log( "Hello!" );
 9199 | })();
 9200 | // "Hello!"
 9201 | ```
 9202 | 
 9203 | This pattern is often used when trying to avoid polluting the global namespace, because all the variables used inside the IIFE (like in any other normal function) are not visible outside its scope.
 9204 | 
 9205 | **Source:** _stackoverflow.com_
 9206 | 
 9207 | #### Q26: What are the advantages and disadvantages of using "use strict"? ⭐⭐⭐
 9208 | **Answer:**
 9209 | 'use strict' is a statement used to enable strict mode to entire scripts or individual functions. Strict mode is a way to opt into a restricted variant of JavaScript.
 9210 | 
 9211 | Advantages:
 9212 | 
 9213 | * Makes it impossible to accidentally create global variables.
 9214 | * Makes assignments which would otherwise silently fail to throw an exception.
 9215 | * Makes attempts to delete undeletable properties throw (where before the attempt would simply have no effect).
 9216 | * Requires that function parameter names be unique.
 9217 | * `this` is undefined in the global context.
 9218 | * It catches some common coding bloopers, throwing exceptions.
 9219 | * It disables features that are confusing or poorly thought out.
 9220 | 
 9221 | Disadvantages:
 9222 | 
 9223 | * Many missing features that some developers might be used to.
 9224 | * No more access to `function.caller` and `function.arguments`.
 9225 | * Concatenation of scripts written in different strict modes might cause issues.
 9226 | 
 9227 | Overall, I think the benefits outweigh the disadvantages, and I never had to rely on the features that strict mode blocks. I would recommend using strict mode.
 9228 | 
 9229 | 
 9230 | **Source:** _github.com/yangshun_
 9231 | 
 9232 | #### Q27: Explain the difference between Object.freeze() vs const ⭐⭐⭐
 9233 | **Answer:**
 9234 | `const` and `Object.freeze` are two completely different things.
 9235 | 
 9236 | * `const` applies to **bindings** ("variables"). It creates an immutable binding, i.e. you cannot assign a new value to the binding.
 9237 | ```js
 9238 | const person = {
 9239 |     name: "Leonardo"
 9240 | };
 9241 | let animal = {
 9242 |     species: "snake"
 9243 | };
 9244 | person = animal; // ERROR "person" is read-only
 9245 | ```
 9246 | * `Object.freeze` works on **values**, and more specifically, *object values*. It makes an object immutable, i.e. you cannot change its properties.
 9247 | ```js
 9248 | let person = {
 9249 |     name: "Leonardo"
 9250 | };
 9251 | let animal = {
 9252 |     species: "snake"
 9253 | };
 9254 | Object.freeze(person);
 9255 | person.name = "Lima"; //TypeError: Cannot assign to read only property 'name' of object
 9256 | console.log(person);
 9257 | ```
 9258 | 
 9259 | **Source:** _stackoverflow.com_
 9260 | 
 9261 | #### Q28: What is Hoisting in JavaScript? ⭐⭐⭐⭐
 9262 | **Answer:**
 9263 | Read Full Answer on 👉 <a href='https://www.fullstack.cafe\blog\web-developer-interview-questions'>FullStack.Cafe</a>
 9264 | 
 9265 | #### Q29: How does the “this” keyword work? Provide some code examples. ⭐⭐⭐⭐
 9266 | **Answer:**
 9267 | Read Full Answer on 👉 <a href='https://www.fullstack.cafe\blog\web-developer-interview-questions'>FullStack.Cafe</a>
 9268 | 
 9269 | #### Q30: Write a recursive function that performs a binary search ⭐⭐⭐⭐
 9270 | **Answer:**
 9271 | Read Full Answer on 👉 <a href='https://www.fullstack.cafe\blog\web-developer-interview-questions'>FullStack.Cafe</a>
 9272 | 
 9273 | #### Q31: What is “closure” in javascript? Provide an example? ⭐⭐⭐⭐
 9274 | **Answer:**
 9275 | Read Full Answer on 👉 <a href='https://www.fullstack.cafe\blog\web-developer-interview-questions'>FullStack.Cafe</a>
 9276 | 
 9277 | #### Q32: Explain difference between: `function Person(){}`, `var person = Person()`, and `var person = new Person()`? ⭐⭐⭐⭐
 9278 | **Answer:**
 9279 | Read Full Answer on 👉 <a href='https://www.fullstack.cafe\blog\web-developer-interview-questions'>FullStack.Cafe</a>
 9280 | 
 9281 | #### Q33: What are the features of Microservices? ⭐⭐⭐
 9282 | **Answer:**
 9283 | *   **Decoupling** – Services within a system are largely decoupled. So the application as a whole can be easily built, altered, and scaled
 9284 | *   **Componentization** – Microservices are treated as independent components that can be easily replaced and upgraded
 9285 | *   **Business Capabilities** – Microservices are very simple and focus on a single capability
 9286 | *   **Autonomy** – Developers and teams can work independently of each other, thus increasing speed
 9287 | *   **Continous** **Delivery** – Allows frequent releases of software, through systematic automation of software creation, testing, and approval
 9288 | *   **Responsibility** – Microservices do not focus on applications as projects. Instead, they treat applications as products for which they are responsible
 9289 | *   **Decentralized Governance** – The focus is on using the right tool for the right job. That means there is no standardized pattern or any technology pattern. Developers have the freedom to choose the best useful tools to solve their problems
 9290 | *   **Agility** – Microservices support agile development. Any new feature can be quickly developed and discarded again
 9291 | 
 9292 | **Source:** _lambdatest.com_
 9293 | 
 9294 | #### Q34: What is npm? ⭐
 9295 | **Answer:**
 9296 | `npm` stands for Node Package Manager. npm provides following two main functionalities:
 9297 | 
 9298 | *   Online repositories for node.js packages/modules which are searchable on [search.nodejs.org](http://search.nodejs.org)
 9299 | *   Command line utility to install packages, do version management and dependency management of Node.js packages.
 9300 | 
 9301 | **Source:** _tutorialspoint.com_
 9302 | 
 9303 | #### Q35: What is the difference between procedural and object-oriented programming? ⭐⭐
 9304 | **Answer:**
 9305 | Procedural programming is based upon the modular approach in which the larger programs are broken into procedures. Each procedure is a set of instructions that are executed one after another. On the other hand, OOP is based upon objects. An object consists of various elements, such as methods and variables.  
 9306 |   
 9307 | Access modifiers are not used in procedural programming, which implies that the entire data can be accessed freely anywhere in the program. In OOP, you can specify the scope of a particular data by using access modifiers - _public_, _private_, _internal_, _protected_, and _protected_ internal.
 9308 | 
 9309 | **Source:** _indiabix.com_
 9310 | 
 9311 | #### Q36: State the features of an interface. ⭐⭐⭐
 9312 | **Answer:**
 9313 | An interface is a template that contains only the signature of methods. The signature of a method consists of the numbers of parameters, the type of parameter (value, reference, or output), and the order of parameters. An interface has no implementation on its own because it contains only the definition of methods without any method body. An interface is defined using the _interface_ keyword. Moreover, you cannot instantiate an interface. The various features of an interface are as follows:  
 9314 | 
 9315 | *   An interface is used to implement multiple inheritance in code. This feature of an interface is quite different from that of abstract classes because a class cannot derive the features of more than one class but can easily implement multiple interfaces.
 9316 | *   It defines a specific set of methods and their arguments.
 9317 | *   Variables in interface must be declared as _public_, _static_, and _final_ while methods must be _public_ and _abstract_.
 9318 | *   A class implementing an interface must implement all of its methods.
 9319 | *   An interface can derive from more than one interface.
 9320 | 
 9321 | **Source:** _indiabix.com_
 9322 | 
 9323 | #### Q37: What is the difference between cohesion and coupling? ⭐⭐⭐⭐
 9324 | **Answer:**
 9325 | Read Full Answer on 👉 <a href='https://www.fullstack.cafe\blog\web-developer-interview-questions'>FullStack.Cafe</a>
 9326 | 
 9327 | #### Q38: What does it mean to “program to an interface”? ⭐⭐⭐⭐⭐
 9328 | **Answer:**
 9329 | Read Full Answer on 👉 <a href='https://www.fullstack.cafe\blog\web-developer-interview-questions'>FullStack.Cafe</a>
 9330 | 
 9331 | #### Q39: What is Reactive Programming? ⭐⭐
 9332 | **Answer:**
 9333 | **Reactive programming is programming with asynchronous data streams.** Event buses or your typical click events are really an asynchronous event stream, on which you can observe and do some side effects. Reactive is that idea on steroids. You are able to create data streams of anything, not just from click and hover events. Streams are cheap and ubiquitous, anything can be a stream: variables, user inputs, properties, caches, data structures, etc. For example, imagine your Twitter feed would be a data stream in the same fashion that click events are. You can listen to that stream and react accordingly.
 9334 | 
 9335 | **Source:** _github.com_
 9336 | 
 9337 | #### Q40: What are different HTTP Methods supported in Restful Web Services? ⭐⭐
 9338 | **Answer:**
 9339 | Restful web services supported HTTP methods are:
 9340 | * GET, 
 9341 | * POST, 
 9342 | * PUT, 
 9343 | * DELETE and 
 9344 | * HEAD.
 9345 | 
 9346 | **Source:** _journaldev.com_
 9347 | 
 9348 | #### Q41: How would you choose between SOAP and REST web services? ⭐⭐⭐
 9349 | **Answer:**
 9350 | Web Services work on client-server model and when it comes to choose between SOAP and REST, it all depends on project requirements. Let’s look at some of the conditions affecting our choice:
 9351 | 
 9352 | * Do you know your web service clients beforehand? If Yes, then you can define a contract before implementation and SOAP seems better choice. But if you don’t then REST seems better choice because you can provide sample request/response and test cases easily for client applications to use later on.
 9353 | * How much time you have? For quick implementation REST is the best choice. You can create web service easily, test it through browser/curl and get ready for your clients.
 9354 | What kind of data format are supported? If only XML then you can go with SOAP but if you think about supporting JSON also in future then go with REST.
 9355 | 
 9356 | **Source:** _journaldev.com_
 9357 | 
 9358 | #### Q42: What are the best practices for caching? ⭐⭐⭐
 9359 | **Answer:**
 9360 | Always keep static contents like images, css, JavaScript cacheable, with expiration date of 2 to 3 days. Never keep expiry date too high.
 9361 | 
 9362 | Dynamic contents should be cached for few hours only.
 9363 | 
 9364 | **Source:** _tutorialspoint.com_
 9365 | 
 9366 | #### Q43: What should be the purpose of OPTIONS method of RESTful web services? ⭐⭐⭐⭐
 9367 | **Answer:**
 9368 | Read Full Answer on 👉 <a href='https://www.fullstack.cafe\blog\web-developer-interview-questions'>FullStack.Cafe</a>
 9369 | 
 9370 | #### Q44: What are the DRY and DIE principles? ⭐⭐⭐
 9371 | **Answer:**
 9372 | In software engineering, **Don't Repeat Yourself (DRY)** or **Duplication is Evil (DIE)** is a principle of software development.
 9373 | 
 9374 | **Source:** _stackoverflow.com_
 9375 | 
 9376 | #### Q45: What is GOD class and why should we avoid it? ⭐⭐⭐⭐
 9377 | **Answer:**
 9378 | Read Full Answer on 👉 <a href='https://www.fullstack.cafe\blog\web-developer-interview-questions'>FullStack.Cafe</a>
 9379 | 
 9380 | #### Q46: What is CORS and how to enable one? ⭐⭐
 9381 | **Answer:**
 9382 | A request for a resource (like an image or a font) outside of the origin is known as a *cross-origin request*. CORS (cross-origin resource sharing) manages cross-origin requests. CORS allows servers to specify who (i.e., which origins) can access the assets on the server, among many other things.
 9383 | 
 9384 | **Access-Control-Allow-Origin** is an HTTP header that defines which foreign origins are allowed to access the content of pages on your domain via scripts using methods such as XMLHttpRequest. 
 9385 | 
 9386 | For example, if your server provides both a website and an API intended for XMLHttpRequest access on a remote websites, only the API resources should return the Access-Control-Allow-Origin header. Failure to do so will allow foreign origins to read the contents of any page on your origin.
 9387 | 
 9388 | ```sh
 9389 | # Allow any site to read the contents of this JavaScript library, so that subresource integrity works
 9390 | Access-Control-Allow-Origin: *
 9391 | ```
 9392 | 
 9393 | **Source:** _infosec.mozilla.org_
 9394 | 
 9395 | #### Q47: What is Cross Site Scripting (XSS)? ⭐⭐
 9396 | **Answer:**
 9397 | By using **Cross Site Scripting (XSS)** technique, users executed malicious scripts (also called payloads) unintentionally by clicking on untrusted links and hence, these scripts pass cookies information to attackers.
 9398 | 
 9399 | **Source:** _allabouttesting.org_
 9400 | 
 9401 | #### Q48: How can I prevent XSS? ⭐⭐
 9402 | **Answer:**
 9403 | XSS can be prevented by sanitizing user input to the application. Always allowed those elements as input which is absolutely essential for that field.
 9404 | 
 9405 | **Source:** _allabouttesting.org_
 9406 | 
 9407 | #### Q49: What is webpack? ⭐
 9408 | **Answer:**
 9409 | **Webpack** is a build tool that puts all of your assets, including Javascript, images, fonts, and CSS, in a dependency graph. Webpack lets you use `require()` in your source code to point to local files, like images, and decide how they're processed in your final Javascript bundle, like replacing the path with a URL pointing to a CDN.
 9410 | 
 9411 | 
 9412 | 
 9413 | **Source:** _blog.andrewray.me_
 9414 | 
 9415 | #### Q50: Describe tree shaking mechanism in webpack ⭐⭐⭐⭐⭐
 9416 | **Answer:**
 9417 | Read Full Answer on 👉 <a href='https://www.fullstack.cafe\blog\web-developer-interview-questions'>FullStack.Cafe</a>
 9418 | 
 9419 | ## [[⬆]](#toc) <a name=50JuniorWebDeveloperInterviewQuestions.TheUltimate2018Guide.>50 Junior Web Developer Interview Questions. The Ultimate 2018 Guide.</a>
 9420 | > Originally published on 👉 <a href='https://www.fullstack.cafe\blog\50-junior-web-developer-interview -questions-and-answers-ultimate-list-2018'>50 Junior Web Developer Interview Questions. The Ultimate 2018 Guide. | FullStack.Cafe</a>
 9421 | 
 9422 | #### Q1: Explain what is Bootstrap? ⭐
 9423 | **Answer:**
 9424 | Bootstrap is CSS/Javascript framework for building the rich web applications with
 9425 | minimal effort. This framework emphasis more on building mobile web
 9426 | applications.
 9427 | 
 9428 | **Source:** _medium.com/@alisonbenhar_
 9429 | 
 9430 | #### Q2: Explain the three main ways to apply CSS styles to a web page ⭐
 9431 | **Answer:**
 9432 | Using the inline style attribute on an element
 9433 | ```html
 9434 | <div>
 9435 |     <p style="color: maroon;"></p>
 9436 | </div>
 9437 | ```
 9438 | Using a `<style>` block in the `<head>` section of your HTML
 9439 | ```html
 9440 | <head>
 9441 |     <title>CSS Refresher</title>
 9442 |     <style>
 9443 |         body {
 9444 |             font-family: sans-serif;
 9445 |             font-size: 1.2em;
 9446 |         }
 9447 |     </style>
 9448 | </head>
 9449 | ```
 9450 | Loading an external CSS file using the `<link>` tag
 9451 | ```html
 9452 | <head>
 9453 |     <title>CSS Refresher</title>
 9454 |     <link rel="stylesheet" href="/css/styles.css" />
 9455 | </head>
 9456 | ```
 9457 | 
 9458 | **Source:** _goskills.com_
 9459 | 
 9460 | #### Q3: What is CSS? ⭐
 9461 | **Answer:**
 9462 | **CSS** stands for **Cascading Style Sheets**. CSS is used to define styles for your web pages, including the design, layout and variations in display for different devices and screen sizes.
 9463 | 
 9464 | CSS was intended to allow web professionals to separate the content and structure of a website's code from the visual design.
 9465 | 
 9466 | **Source:** _w3schools.com_
 9467 | 
 9468 | #### Q4: Explain the CSS “box model” and the layout components that it consists of ⭐⭐
 9469 | **Answer:**
 9470 | The CSS box model is a rectangular layout paradigm for HTML elements that consists of the following:
 9471 | 
 9472 | * **Content** - The content of the box, where text and images appear
 9473 | * **Padding** - A transparent area surrounding the content (i.e., the amount of space between the border and the content)
 9474 | * **Border** - A border surrounding the padding (if any) and content
 9475 | * **Margin** - A transparent area surrounding the border (i.e., the amount of space between the border and any neighboring elements)
 9476 | 
 9477 | **Source:** _toptal.com_
 9478 | 
 9479 | #### Q5: Describe floats and how they work ⭐⭐
 9480 | **Answer:**
 9481 | *Float* is a CSS positioning property. Floated elements remain a part of the flow of the web page. This is distinctly different than page elements that use absolute positioning. Absolutely positioned page elements are removed from the flow of the webpage.
 9482 | 
 9483 | ```css
 9484 | #sidebar {
 9485 |   float: right; // left right none inherit			
 9486 | }
 9487 | ```
 9488 | The CSS clear property can be used to be positioned below `left`/`right`/`both` floated elements.
 9489 | 
 9490 | **Source:** _css-tricks.com_
 9491 | 
 9492 | #### Q6: Have you played around with the new CSS Flexbox or Grid specs? ⭐⭐
 9493 | **Answer:**
 9494 | Yes. Flexbox is mainly meant for 1-dimensional layouts while Grid is meant for 2-dimensional layouts.
 9495 | 
 9496 | Flexbox solves many common problems in CSS, such as vertical centering of elements within a container, sticky footer, etc. Bootstrap and Bulma are based on Flexbox, and it is probably the recommended way to create layouts these days. Have tried Flexbox before but ran into some browser incompatibility issues (Safari) in using `flex-grow`, and I had to rewrite my code using `inline-blocks` and math to calculate the widths in percentages, it wasn't a nice experience.
 9497 | 
 9498 | Grid is by far the most intuitive approach for creating grid-based layouts (it better be!) but browser support is not wide at the moment.
 9499 | 
 9500 | **Source:** _codeburst.io_
 9501 | 
 9502 | #### Q7: What existing CSS frameworks have you used locally, or in production? How would you change/improve them? ⭐⭐
 9503 | **Answer:**
 9504 | * **Bootstrap** - Slow release cycle. Bootstrap 4 has been in alpha for almost 2 years. Add a spinner button component, as it is widely used.
 9505 | * **Semantic UI** - Source code structure makes theme customization extremely hard to understand. Its unconventional theming system is a pain to customize. Hardcoded config path within the vendor library. Not well-designed for overriding variables unlike in Bootstrap.
 9506 | * **Bulma** - A lot of non-semantic and superfluous classes and markup required. Not backward compatible. Upgrading versions breaks the app in subtle manners.
 9507 | 
 9508 | **Source:** _codeburst.io_
 9509 | 
 9510 | #### Q8: What is DOM (Document Object Model) and how is it linked to CSS? ⭐⭐
 9511 | **Answer:**
 9512 | The *Document Object Model (DOM)* is a cross-platform and language-independent *application programming interface* that treats an HTML, XHTML, or XML document as a tree structure wherein each node is an object representing a part of the document. 
 9513 | 
 9514 | With the Document Object Model, programmers can create and build documents, navigate their structure, and add, modify, or delete elements and content. The DOM specifies interfaces which may be used to manage XML or HTML documents. 
 9515 | 
 9516 | When a browser displays a document, it must combine the document's content with its style information. The browser converts HTML and CSS into the DOM (Document Object Model). The DOM represents the document in the computer's memory. It combines the document's content with its style.
 9517 | 
 9518 | **Source:** _en.wikipedia.org_
 9519 | 
 9520 | #### Q9: What is CSS preprocessor and why to user one? ⭐⭐⭐
 9521 | **Answer:**
 9522 | A **CSS preprocessor** is a program that lets you generate CSS from the preprocessor's own unique syntax. There are many CSS preprocessors to choose from, however most CSS preprocessors will add some features that don't exist in pure CSS, such as mixin, nesting selector, inheritance selector, and so on. These features make the CSS structure more readable and easier to maintain.
 9523 | 
 9524 | Here are a few of the most popular CSS preprocessors:
 9525 | 
 9526 | * SASS (SCSS)
 9527 | * LESS
 9528 | * Stylus
 9529 | * PostCSS
 9530 | 
 9531 | **Source:** _developer.mozilla.org_
 9532 | 
 9533 | #### Q10: How to create a zebra striped table with CSS? ⭐⭐⭐
 9534 | **Answer:**
 9535 | To create a zebra-striped table, use the `nth-child()` selector and add a background-color to all even (or odd) table rows:
 9536 | ```css
 9537 | tr:nth-child(even) {
 9538 |     background-color: #f2f2f2
 9539 | }
 9540 | ```
 9541 | 
 9542 | **Source:** _w3schools.com_
 9543 | 
 9544 | #### Q11: What is a Grid System in CSS? ⭐⭐⭐
 9545 | **Answer:**
 9546 | A grid system is a structure that allows for content to be stacked both vertically and horizontally in a consistent and easily manageable fashion. Grid systems include two key components: rows and columns.
 9547 | 
 9548 | Some Grid Systems:
 9549 | * Simple Grid
 9550 | * Pure
 9551 | * Flexbox Grid
 9552 | * Bootstrap
 9553 | * Foundation
 9554 | 
 9555 | **Source:** _sitepoint.com_
 9556 | 
 9557 | #### Q12: What is Singleton pattern? ⭐
 9558 | **Answer:**
 9559 | **Singleton pattern** comes under *creational* patterns category and introduces a single class which is responsible to create an object while making sure that only single object gets created. This class provides a way to access its only object which can be accessed directly without need to instantiate the object of the class.
 9560 | 
 9561 | <div class="text-center">
 9562 | <img src="https://upload.wikimedia.org/wikipedia/commons/thumb/f/fb/Singleton_UML_class_diagram.svg/220px-Singleton_UML_class_diagram.svg.png" class="img-fluid"/>
 9563 | </div>
 9564 | 
 9565 | 
 9566 | **Source:** _refactoring.guru_
 9567 | 
 9568 | #### Q13: What is Dependency Injection? ⭐⭐
 9569 | **Answer:**
 9570 | *Dependency injection* makes it easy to create loosely coupled components, which typically means that components consume functionality defined by interfaces without having any first-hand knowledge of which implementation classes are being used.
 9571 | 
 9572 | *Dependency injection* makes it easier to change the behavior of an application by changing the components that implement the interfaces that define application features. It also results in components that are easier to isolate for unit testing.
 9573 | 
 9574 | **Source:** _Pro ASP.NET Core MVC 2_
 9575 | 
 9576 | #### Q14: What is Observer pattern? ⭐⭐⭐
 9577 | **Answer:**
 9578 | **Observer pattern**  (also known as *Publish-Subscribe Pattern*) is used when there is one-to-many relationship between objects such as if one object is modified, its dependent objects are to be notified automatically. Observer pattern falls under _behavioral_ pattern category.
 9579 | 
 9580 | An object with a one-to-many relationship with other objects who are interested in its state is called the _subject_ or _publisher_. The _observers_ are notified whenever the state of the _subject_ changes and can act accordingly. The _subject_ can have any number of dependent _observers_ which it notifies, and any number of _observers_ can subscribe to the _subject_ to receive such notifications.
 9581 | 
 9582 | Observer pattern uses two actor classes:
 9583 | * The Observer (os Subscriber) abstract class provides an `update()` method which will be called by the subject to notify it of the subject’s state change. 
 9584 | * The Subject (or Publisher) class is also an abstract class and defines four primary methods: `attach()`, `detach()`, `setState()`, and `notify()`
 9585 | 
 9586 | 
 9587 | 
 9588 | <div class="text-center">
 9589 | <img src="https://upload.wikimedia.org/wikipedia/commons/0/01/W3sDesign_Observer_Design_Pattern_UML.jpg" class="img-fluid"/>
 9590 | </div>
 9591 | 
 9592 | **Source:** _sitepoint.com_
 9593 | 
 9594 | #### Q15: What is meant by Continuous Integration? ⭐
 9595 | **Answer:**
 9596 | *Continuous Integration (CI)* is a development practice that requires developers to integrate code into a shared repository several times a day. Each check-in is then verified by an automated build, allowing teams to detect problems early. 
 9597 | 
 9598 | **Source:** _edureka.co_
 9599 | 
 9600 | #### Q16: What do you know about serverless model? ⭐⭐⭐
 9601 | **Answer:**
 9602 | **Serverless** refers to a model where the existence of servers is hidden from developers. It means you no longer have to deal with capacity, deployments, scaling and fault tolerance and OS. It will essentially reducing maintenance efforts and allow developers to quickly focus on developing codes.
 9603 | 
 9604 | Examples are:
 9605 | * Amazon AWS Lambda
 9606 | * Azure Functions
 9607 | 
 9608 | **Source:** _linoxide.com_
 9609 | 
 9610 | #### Q17: What is Git? ⭐
 9611 | **Answer:**
 9612 | Git is a Distributed Version Control system (DVCS). It can track changes to a file and allows you to revert back to any particular change.
 9613 | 
 9614 | Its distributed architecture provides many advantages over other Version Control Systems (VCS) like SVN one major advantage is that it does not rely on a central server to store all the versions of a project’s files. 
 9615 | 
 9616 | **Source:** _edureka.co_
 9617 | 
 9618 | #### Q18: How does the Centralized Workflow work? ⭐⭐
 9619 | **Answer:**
 9620 | The **Centralized Workflow** uses a central repository to serve as the single point-of-entry for all changes to the project. The default development branch is called master and all changes are committed into this branch.
 9621 | 
 9622 | Developers start by cloning the central repository. In their own local copies of the project, they edit files and commit changes. These new commits are stored locally.
 9623 | 
 9624 | To publish changes to the official project, developers *push* their local master branch to the central repository. Before the developer can publish their feature, they need to *fetch* the updated central commits and rebase their changes on top of them. 
 9625 | 
 9626 | Compared to other workflows, the Centralized Workflow has no defined pull request or forking patterns. 
 9627 | 
 9628 | **Source:** _atlassian.com_
 9629 | 
 9630 | #### Q19: You need to update your local repos. What git commands will you use? ⭐⭐
 9631 | **Answer:**
 9632 | It’s a two steps process. First you fetch the changes from a remote named origin:
 9633 | 
 9634 | ```sh
 9635 | git fetch origin
 9636 | ```
 9637 | Then you merge a branch master to local:
 9638 | 
 9639 | ```sh
 9640 | git merge origin/master
 9641 | ```
 9642 | Or simply:
 9643 | 
 9644 | ```sh
 9645 | git pull origin master
 9646 | ```
 9647 | If origin is a default remote and ‘master’ is default branch, you can drop it eg. `git pull`.
 9648 | 
 9649 | **Source:** _samwize.com_
 9650 | 
 9651 | #### Q20: Could you explain the Gitflow workflow? ⭐⭐⭐
 9652 | **Answer:**
 9653 | Gitflow workflow employs two parallel *long-running* branches to record the history of the project, `master` and `develop`:
 9654 | * **Master** -  is always ready to be released on LIVE, with everything fully tested and approved (production-ready).
 9655 |  * **Hotfix** - Maintenance or “hotfix” branches are used to quickly patch production releases. Hotfix branches are a lot like release branches and feature branches except they're based on `master` instead of `develop`.
 9656 | 
 9657 | 
 9658 | * **Develop** - is the branch to which all feature branches are merged and where all tests are performed. Only when everything’s been thoroughly checked and fixed it can be merged to the `master`.
 9659 |  * **Feature** - Each new feature should reside in its own branch, which can be pushed to the `develop` branch as their parent one.
 9660 | 
 9661 | <div class="text-center">
 9662 | <img src="https://res.cloudinary.com/practicaldev/image/fetch/s--pLQxGakq--/c_limit%2Cf_auto%2Cfl_progressive%2Cq_auto%2Cw_880/https://wac-cdn.atlassian.com/dam/jcr:61ccc620-5249-4338-be66-94d563f2843c/05%2520%282%29.svg%3FcdnVersion%3Dji" class="img-fluid" style="max-width: 500px;"/>
 9663 | </div>
 9664 | 
 9665 | 
 9666 | **Source:** _atlassian.com_
 9667 | 
 9668 | #### Q21: Explain meta tags in HTML ⭐
 9669 | **Answer:**
 9670 | - **Meta tags** always go inside **head tag** of the HTML page
 9671 | - **Meta tags** is always passed as name/value pairs
 9672 | - **Meta tags** are not displayed on the page but intended for the browser
 9673 | - **Meta tags** can contain information about **character encoding**, **description**, **title** of the document etc,
 9674 | 
 9675 | **Example**:
 9676 | 
 9677 | ```html
 9678 | <!DOCTYPE html>
 9679 | <html>
 9680 | <head>
 9681 |   <meta name="description" content="I am a web page with description"> 
 9682 |   <title>Home Page</title>
 9683 | </head>
 9684 | <body>
 9685 |   
 9686 | </body>
 9687 | </html>
 9688 | ```
 9689 | 
 9690 | 
 9691 | **Source:** _github.com/FuelFrontend_
 9692 | 
 9693 | #### Q22: Write a HTML table tag sequence that outputs the following ⭐
 9694 | **Answer:**
 9695 | Write a HTML table tag sequence that outputs the following:
 9696 | ```
 9697 | 50 pcs 100 500
 9698 | 10 pcs 5 50
 9699 | ```
 9700 | 
 9701 | **Answer:**
 9702 | ```html
 9703 | <table>
 9704 |   <tr>
 9705 |     <td>50 pcs</td>
 9706 |     <td>100</td>
 9707 |     <td>500</td>
 9708 |   </tr>
 9709 |   <tr>
 9710 |     <td>10 pcs</td>
 9711 |     <td>5</td>
 9712 |     <td>50</td>
 9713 |   </tr>
 9714 | </table>
 9715 | ```
 9716 | 
 9717 | **Source:** _toptal.com_
 9718 | 
 9719 | #### Q23: What is the difference between span and div? ⭐⭐
 9720 | **Answer:**
 9721 | * `div` is a block element
 9722 | * `span` is inline element 
 9723 | 
 9724 | For bonus points, you could point out that it’s illegal to place a block element inside an inline element, and that while `div` can have a `p` tag, and a `p` tag can have a `span`, it is not possible for `span` to have a `div` or `p` tag inside.
 9725 | 
 9726 | **Source:** _thatjsdude.com_
 9727 | 
 9728 | #### Q24: How Can I Get Indexed Better by Search Engines? ⭐⭐
 9729 | **Answer:**
 9730 | It is possible to get indexed better by placing the following two statements in the `<HEAD>` part of your documents:
 9731 | 
 9732 | ```html
 9733 | <META NAME="keywords" CONTENT="keyword keyword keyword keyword">
 9734 | <META NAME="description" CONTENT="description of your site">
 9735 | ```
 9736 | Both may contain up to 1022 characters. If a keyword is used more than 7 times, the keywords tag will be ignored altogether. Also, you cannot put markup (other than entities) in the description or keywords list.
 9737 | 
 9738 | **Source:** _freejavaguide.com_
 9739 | 
 9740 | #### Q25: Explain the difference between cookies, session and local storage ⭐⭐⭐
 9741 | **Answer:**
 9742 | **Cookies**
 9743 | 
 9744 | - **Limited** storage space **4096 bytes / ~4 kb**
 9745 | - Only allow to store data as **strings**
 9746 | - Stored data is sent back to server on every **HTTP request** such as HTML, CSS, Images etc,
 9747 | - Can store only **20 cookies per domain**
 9748 | - In total **300** cookies are allowed on a site
 9749 | - Setting **HTTP only** flag will **prevent accessing cookies** via javascript
 9750 | - Can set **expiration** duration for auto deletion (can be set either from server or client)
 9751 | 
 9752 | **Example**:
 9753 | 
 9754 | ```js
 9755 | // Set with expiration & path
 9756 | document.cookie = "name=Gokul; expires=Thu, 18 Dec 2016 12:00:00 UTC; path=/;";
 9757 | 
 9758 | // Get
 9759 | document.cookie;
 9760 | 
 9761 | // Delete by setting empty value and same path
 9762 | document.cookie = "name=; expires=Thu, 18 Dec 2016 12:00:00 UTC; path=/;";
 9763 | ```
 9764 | 
 9765 | **Session Storage**
 9766 | 
 9767 | - Storage space is **5 mb / ~5120 kb**
 9768 | - Storage space may **vary a little** based on the browser
 9769 | - Only allow to store data as **strings**
 9770 | - Data is available per **window or tab**
 9771 | - Once window or tab is closed stored data is **deleted**
 9772 | - Data will be **only available on same origin**
 9773 | 
 9774 | **Example**:
 9775 | 
 9776 | ```js
 9777 | // Set
 9778 | sessionStorage.setItem("name", "gokul");
 9779 | 
 9780 | // Get
 9781 | sessionStorage.getItem("name"); // gokul
 9782 | 
 9783 | // Delete
 9784 | sessionStorage.removeItem("name"); 
 9785 | 
 9786 | // Delete All
 9787 | sessionStorage.clear();
 9788 | ```
 9789 | 
 9790 | **Local Storage**
 9791 | 
 9792 | - Storage space is **5 mb / ~5120 kb**
 9793 | - Storage space may **vary a little** based on the browser
 9794 | - Only allow to store data as **strings**
 9795 | - Data will be **only available on same origin**
 9796 | - Data is **persistant** (untill explicitly deleted)
 9797 | - API is similar to session storage
 9798 | 
 9799 | **Example**:
 9800 | 
 9801 | ```js
 9802 | // Set
 9803 | localStorage.setItem("name", "gokul");
 9804 | 
 9805 | // Get
 9806 | localStorage.getItem("name"); // gokul
 9807 | 
 9808 | // Delete
 9809 | localStorage.removeItem("name"); 
 9810 | 
 9811 | // Delete All
 9812 | localStorage.clear();
 9813 | ```
 9814 | 
 9815 | **Source:** _github.com/FuelFrontend_
 9816 | 
 9817 | #### Q26: What's new in HTML 5? ⭐⭐⭐
 9818 | **Answer:**
 9819 | HTML 5 adds a lot of new features to the HTML specification
 9820 | 
 9821 | **New Doctype**
 9822 | 
 9823 | Still using that pesky, impossible-to-memorize XHTML doctype?
 9824 | 
 9825 | ```html
 9826 | <!DOCTYPE html PUBLIC "-//W3C//DTD XHTML 1.0 Transitional//EN"
 9827 |     "http://www.w3.org/TR/xhtml1/DTD/xhtml1-transitional.dtd">
 9828 | ```
 9829 | 
 9830 | If so, why? Switch to the new HTML5 doctype. You'll live longer -- as Douglas Quaid might say.
 9831 | 
 9832 | ```html
 9833 | <!DOCTYPE html>
 9834 | ```
 9835 | 
 9836 | **New Structure**
 9837 | 
 9838 | - `<section>` - to define sections of pages
 9839 | - `<header>` - defines the header of a page
 9840 | - `<footer>` - defines the footer of a page
 9841 | - `<nav>` - defines the navigation on a page
 9842 | - `<article>` - defines the article or primary content on a page
 9843 | - `<aside>` - defines extra content like a sidebar on a page
 9844 | - `<figure>` - defines images that annotate an article
 9845 | 
 9846 | **New Inline Elements**
 9847 | 
 9848 | These inline elements define some basic concepts and keep them semantically marked up, mostly to do with time:
 9849 | 
 9850 | - `<mark>` - to indicate content that is marked in some fashion
 9851 | - `<time>` - to indicate content that is a time or date
 9852 | - `<meter>` - to indicate content that is a fraction of a known range - such as disk usage
 9853 | - `<progress>` - to indicate the progress of a task towards completion
 9854 | 
 9855 | **New Form Types**
 9856 | 
 9857 | - `<input type="datetime">`
 9858 | - `<input type="datetime-local">`
 9859 | - `<input type="date">`
 9860 | - `<input type="month">`
 9861 | - `<input type="week">`
 9862 | - `<input type="time">`
 9863 | - `<input type="number">`
 9864 | - `<input type="range">`
 9865 | - `<input type="email">`
 9866 | - `<input type="url">`
 9867 | 
 9868 | **New Elements**
 9869 | 
 9870 | There are a few exciting new elements in HTML 5:
 9871 | 
 9872 | - `<canvas>` - an element to give you a drawing space in JavaScript on your Web pages. It can let you add images or graphs to tool tips or just create dynamic graphs on your Web pages, built on the fly.
 9873 | - `<video>` - add video to your Web pages with this simple tag.
 9874 | - `<audio>` - add sound to your Web pages with this simple tag.
 9875 | 
 9876 | **No More Types for Scripts and Links**
 9877 | 
 9878 | You possibly still add the `type` attribute to your `link` and `script` tags.
 9879 | 
 9880 | ```html
 9881 | <link rel="stylesheet" href="path/to/stylesheet.css" type="text/css" />
 9882 | <script type="text/javascript" src="path/to/script.js"></script>
 9883 | ```
 9884 | 
 9885 | This is no longer necessary. It's implied that both of these tags refer to stylesheets and scripts, respectively. As such, we can remove the `type` attribute all together.
 9886 | 
 9887 | ```html
 9888 | <link rel="stylesheet" href="path/to/stylesheet.css" />
 9889 | <script src="path/to/script.js"></script>
 9890 | ```
 9891 | 
 9892 | **Make your content editable**
 9893 | 
 9894 | The new browsers have a nifty new attribute that can be applied to elements, called `contenteditable`. As the name implies, this allows the user to edit any of the text contained within the element, including its children. There are a variety of uses for something like this, including an app as simple as a to-do list, which also takes advantage of local storage.
 9895 | 
 9896 | ```html
 9897 | <h2> To-Do List </h2>
 9898 | <ul contenteditable="true">
 9899 |   <li> Break mechanical cab driver. </li>
 9900 |   <li> Drive to abandoned factory
 9901 |   <li> Watch video of self </li>
 9902 | </ul>
 9903 | ```
 9904 | 
 9905 | **Attributes**
 9906 | 
 9907 | - `require` to mention the form field is required
 9908 | - `autofocus` puts the cursor on the input field
 9909 | 
 9910 | **Source:** _github.com/FuelFrontend_
 9911 | 
 9912 | #### Q27: What is the purpose of cache busting and how can you achieve it? ⭐⭐⭐
 9913 | **Answer:**
 9914 | Browsers have a cache to temporarily store files on websites so they don't need to be re-downloaded again when switching between pages or reloading the same page. The server is set up to send headers that tell the browser to store the file for a given amount of time. This greatly increases website speed and preserves bandwidth.
 9915 | 
 9916 | However, it can cause problems when the website has been changed by developers because the user's cache still references old files. This can either leave them with old functionality or break a website if the cached CSS and JavaScript files are referencing elements that no longer exist, have moved or have been renamed.
 9917 | 
 9918 | Cache busting is the process of forcing the browser to download the new files. This is done by naming the file something different to the old file.
 9919 | 
 9920 | A common technique to force the browser to re-download the file is to append a query string to the end of the file.
 9921 | 
 9922 | * `src="js/script.js"` => `src="js/script.js?v=2"`
 9923 | 
 9924 | The browser considers it a different file but prevents the need to change the file name.
 9925 | 
 9926 | **Source:** _css-tricks.com_
 9927 | 
 9928 | #### Q28: Explain equality in JavaScript ⭐
 9929 | **Answer:**
 9930 | JavaScript has both strict and type–converting comparisons: 
 9931 | * **Strict comparison (e.g., ===)** checks for value equality without allowing *coercion*
 9932 | * **Abstract comparison (e.g. ==)** checks for value equality with *coercion* allowed
 9933 | 
 9934 | ```js
 9935 | var a = "42";
 9936 | var b = 42;
 9937 | 
 9938 | a == b;			// true
 9939 | a === b;		// false
 9940 | ```
 9941 | Some simple equalityrules:
 9942 | * If either value (aka side) in a comparison could be the `true` or `false` value, avoid `==` and use `===`.
 9943 | * If either value in a comparison could be of these specific values (`0`, `""`, or `[]` -- empty array), avoid `==` and use `===`.
 9944 | * In all other cases, you're safe to use `==`. Not only is it safe, but in many cases it simplifies your code in a way that improves readability.
 9945 | 
 9946 | #### Q29: What is Scope in JavaScript? ⭐
 9947 | **Answer:**
 9948 | In JavaScript, each function gets its own *scope*. Scope is basically a collection of variables as well as the rules for how those variables are accessed by name. Only code inside that function can access that function's scoped variables.
 9949 | 
 9950 | A variable name has to be unique within the same scope. A scope can be nested inside another scope. If one scope is nested inside another, code inside the innermost scope can access variables from either scope.
 9951 | 
 9952 | #### Q30: Explain event bubbling and how one may prevent it ⭐⭐
 9953 | **Answer:**
 9954 | **Event bubbling** is the concept in which an event triggers at the deepest possible element, and triggers on parent elements in nesting order. As a result, when clicking on a child element one may exhibit the handler of the parent activating.
 9955 | 
 9956 | One way to prevent event bubbling is using `event.stopPropagation()` or `event.cancelBubble` on IE < 9.
 9957 | 
 9958 | **Source:** _https://github.com/kennymkchan_
 9959 | 
 9960 | #### Q31: Given a string, reverse each word in the sentence ⭐⭐
 9961 | **Details:**
 9962 | For example `Welcome to this Javascript Guide!` should be become `emocleW ot siht tpircsavaJ !ediuG`
 9963 | 
 9964 | **Answer:**
 9965 | ```js
 9966 | var string = "Welcome to this Javascript Guide!";
 9967 | 
 9968 | // Output becomes !ediuG tpircsavaJ siht ot emocleW
 9969 | var reverseEntireSentence = reverseBySeparator(string, "");
 9970 | 
 9971 | // Output becomes emocleW ot siht tpircsavaJ !ediuG
 9972 | var reverseEachWord = reverseBySeparator(reverseEntireSentence, " ");
 9973 | 
 9974 | function reverseBySeparator(string, separator) {
 9975 |   return string.split(separator).reverse().join(separator);
 9976 | }
 9977 | ```
 9978 | 
 9979 | **Source:** _https://github.com/kennymkchan_
 9980 | 
 9981 | #### Q32: What does "use strict" do? ⭐⭐
 9982 | **Answer:**
 9983 | The `use strict` literal is entered at the top of a JavaScript program or at the top of a function and it helps you write safer JavaScript code by throwing an error if a global variable is created by mistake. For example, the following program will throw an error:
 9984 | 
 9985 | ```js
 9986 | function doSomething(val) {
 9987 |   "use strict"; 
 9988 |   x = val + 10;
 9989 | }`
 9990 | ```
 9991 | 
 9992 | It will throw an error because `x` was not defined and it is being set to some value in the global scope, which isn't allowed with `use strict` The small change below fixes the error being thrown:
 9993 | 
 9994 | ```js
 9995 | function doSomething(val) {
 9996 |   "use strict"; 
 9997 |   var x = val + 10;
 9998 | }
 9999 | ```
10000 | 
10001 | **Source:** _coderbyte.com_
10002 | 
10003 | #### Q33: What is a Polyfill? ⭐⭐
10004 | **Answer:**
10005 | A polyfill is essentially the specific code (or plugin) that would allow you to have some specific functionality that you expect in current or “modern” browsers to also work in other browsers that do not have the support for that functionality built in.
10006 | * Polyfills are not part of the HTML5 standard
10007 | * Polyfilling is not limited to Javascript
10008 | 
10009 | **Source:** _programmerinterview.com_
10010 | 
10011 | #### Q34: Explain Null and Undefined in JavaScript ⭐⭐
10012 | **Answer:**
10013 | JavaScript (and by extension TypeScript) has two bottom types: `null` and `undefined`. They are *intended* to mean different things:
10014 | * Something hasn't been initialized : `undefined`.
10015 | * Something is currently unavailable: `null`.
10016 | 
10017 | #### Q35: What will be the output of the following code? ⭐⭐⭐
10018 | **Details:**
10019 | ```js
10020 | var y = 1;
10021 | if (function f() {}) {
10022 |   y += typeof f;
10023 | }
10024 | console.log(y);
10025 | ```
10026 | 
10027 | **Answer:**
10028 | Above code would give output `1undefined`. If condition statement evaluate using `eval` so `eval(function f() {})` which return `function f() {}` which is true so inside if statement code execute. `typeof f` return undefined because if statement code execute at run time, so statement inside `if` condition evaluated at run time.  
10029 | 
10030 | ```js
10031 | var k = 1;
10032 | if (1) {
10033 |   eval(function foo() {});
10034 |   k += typeof foo;
10035 | }
10036 | console.log(k);
10037 | ```
10038 | 
10039 | Above code will also output `1undefined`.
10040 | 
10041 | ```js
10042 | var k = 1;
10043 | if (1) {
10044 |   function foo() {};
10045 |   k += typeof foo;
10046 | }
10047 | console.log(k); // output 1function
10048 | ```
10049 | 
10050 | **Source:** _github.com/ganqqwerty_
10051 | 
10052 | #### Q36: How to compare two objects in JavaScript? ⭐⭐⭐
10053 | **Answer:**
10054 | Two non-primitive values, like objects (including function and array) held by reference, so both `==` and `===` comparisons will simply check whether the references match, not anything about the underlying values.
10055 | 
10056 | For example, `arrays` are by default coerced to strings by simply joining all the values with commas (`,`) in between. So two arrays with the same contents would not be `==` equal:
10057 | 
10058 | ```js
10059 | var a = [1,2,3];
10060 | var b = [1,2,3];
10061 | var c = "1,2,3";
10062 | 
10063 | a == c;		// true
10064 | b == c;		// true
10065 | a == b;		// false
10066 | ```
10067 | For *deep object comparison* use external libs like `deep-equal` or implement your own recursive equality algorithm.
10068 | 
10069 | 
10070 | #### Q37: Given two strings, return true if they are anagrams of one another ⭐⭐⭐
10071 | **Details:**
10072 | For example: `Mary` is an anagram of `Army`
10073 | 
10074 | **Answer:**
10075 | ```js
10076 | var firstWord = "Mary";
10077 | var secondWord = "Army";
10078 | 
10079 | isAnagram(firstWord, secondWord); // true
10080 | 
10081 | function isAnagram(first, second) {
10082 |   // For case insensitivity, change both words to lowercase.
10083 |   var a = first.toLowerCase();
10084 |   var b = second.toLowerCase();
10085 | 
10086 |   // Sort the strings, and join the resulting array to a string. Compare the results
10087 |   a = a.split("").sort().join("");
10088 |   b = b.split("").sort().join("");
10089 | 
10090 |   return a === b;
10091 | }
10092 | ```
10093 | 
10094 | **Source:** _https://github.com/kennymkchan_
10095 | 
10096 | #### Q38: Explain the difference between "undefined" and "not defined" in JavaScript ⭐⭐⭐
10097 | **Answer:**
10098 | In JavaScript if you try to use a variable that doesn't exist and has not been declared, then JavaScript will throw an error `var name is not defined` and the script will stop execute thereafter. But If you use `typeof undeclared_variable` then it will return `undefined`.
10099 | 
10100 | Before starting further discussion let's understand the difference between declaration and definition.
10101 | 
10102 | `var x` is a declaration because you are not defining what value it holds yet, but you are declaring its existence and the need of memory allocation.
10103 | 
10104 | ```javascript
10105 | var x; // declaring x
10106 | console.log(x); //output: undefined
10107 | ```
10108 | 
10109 | `var x = 1` is both declaration and definition (also we can say we are doing initialisation), Here declaration and assignment of value happen inline for variable x, In JavaScript every variable declaration and function declaration brings to the top of its current scope in which it's declared then assignment happen in order this term is called `hoisting`.
10110 | 
10111 | A variable that is declared but not define and when we try to access it, It will result `undefined`.
10112 | 
10113 | ```javascript
10114 | var x; // Declaration
10115 | if(typeof x === 'undefined') // Will return true
10116 | ```
10117 | 
10118 | > A variable that neither declared nor defined when we try to reference such variable then It result `not defined`.
10119 | 
10120 | ```javascript
10121 | console.log(y);  // Output: ReferenceError: y is not defined
10122 | ```
10123 | 
10124 | **Source:** _stackoverflow.com_
10125 | 
10126 | #### Q39: Describe closure concept in JavaScript as best as you could ⭐⭐⭐
10127 | **Answer:**
10128 | Consider:
10129 | ```js
10130 | function makeAdder(x) {
10131 | 	// parameter `x` is an inner variable
10132 | 
10133 | 	// inner function `add()` uses `x`, so
10134 | 	// it has a "closure" over `x`
10135 | 	function add(y) {
10136 | 		return y + x;
10137 | 	};
10138 | 
10139 | 	return add;
10140 | }
10141 | ```
10142 | Reference to inner `add` function returned is able to remember what `x` value was passed to makeAdder function call.
10143 | 
10144 | ```js
10145 | var plusOne = makeAdder( 1 ); // x is 1, plusOne has a reference to add(y)
10146 | var plusTen = makeAdder( 10 ); // x is 10
10147 | 
10148 | plusOne(3); // 1 (x) + 3 (y) = 4
10149 | plusTen(13); // 10 (x) + 13 (y) = 23 
10150 | 
10151 | ```
10152 | In C and most other common languages, after a function returns, all the local variables are no longer accessible because the stack-frame is destroyed.
10153 | 
10154 | In JavaScript, if you declare a function within another function, then the local variables can remain accessible after returning from the function you called.
10155 | 
10156 | A closure is a stack frame which is allocated when a function starts its execution, and not freed after the function returns (as if a 'stack frame' were allocated on the heap rather than the stack!).  In JavaScript, you can think of a function reference variable as having both a pointer to a function as well as a hidden pointer to a closure.
10157 | 
10158 | 
10159 | **Source:** _https://stackoverflow.com/questions/111102/how-do-javascript-closures-work_
10160 | 
10161 | #### Q40: What is npm? ⭐
10162 | **Answer:**
10163 | `npm` stands for Node Package Manager. npm provides following two main functionalities:
10164 | 
10165 | *   Online repositories for node.js packages/modules which are searchable on [search.nodejs.org](http://search.nodejs.org)
10166 | *   Command line utility to install packages, do version management and dependency management of Node.js packages.
10167 | 
10168 | **Source:** _tutorialspoint.com_
10169 | 
10170 | #### Q41: What is Node.js? ⭐
10171 | **Answer:**
10172 | Node.js is a web application framework built on Google Chrome's JavaScript Engine (V8 Engine).
10173 | 
10174 | Node.js comes with runtime environment on which a Javascript based script can be interpreted and executed (It is analogus to JVM to JAVA byte code). This runtime allows to execute a JavaScript code on any machine outside a browser. Because of this runtime of Node.js, JavaScript is now can be executed on server as well.
10175 | 
10176 | *Node.js = Runtime Environment + JavaScript Library*
10177 | 
10178 | **Source:** _tutorialspoint.com_
10179 | 
10180 | #### Q42: What is global installation of dependencies? ⭐⭐
10181 | **Answer:**
10182 | Globally installed packages/dependencies are stored in **<user-directory>**/npm directory. Such dependencies can be used in CLI (Command Line Interface) function of any node.js but can not be imported using require() in Node application directly. To install a Node project globally use -g flag.
10183 | 
10184 | **Source:** _tutorialspoint.com_
10185 | 
10186 | #### Q43: What is Sass? ⭐⭐
10187 | **Answer:**
10188 | **Sass** or **Syntactically Awesome StyleSheets** is a *CSS* preprocessor that adds power and elegance to the basic language. It allows you to use variables, nested rules, mixins, inline imports, and more, all with a fully CSS-compatible syntax. Sass helps keep large stylesheets well-organized, and get small stylesheets up and running quickly.
10189 | 
10190 | A *CSS preprocessor* is a scripting language that extends CSS by allowing developers to write code in one language and then compile it into CSS. 
10191 | 
10192 | 
10193 | **Source:** _sass-lang.com_
10194 | 
10195 | #### Q44: Describe what User Interface (UI) Design does mean for you? ⭐⭐
10196 | **Answer:**
10197 | **User Interface (UI) design** is the design of software or websites with the focus on the user’s experience and interaction. The goal of user interface design is to make the user’s interaction as simple and efficient as possible. Good user interface design puts emphasis on *goals* and *completing tasks*, and good UI design never draws more attention to itself than enforcing user goals.
10198 | 
10199 | **Source:** _uxplanet.org_
10200 | 
10201 | #### Q45: What is SQL injection? ⭐
10202 | **Answer:**
10203 | Injection attacks stem from a lack of strict separation between program instructions (i.e., code) and user-provided (or external) input. This allows an attacker to inject malicious code into a data snippet. 
10204 | 
10205 | *SQL injection* is one of the most common types of injection attack. To carry it out, an attacker provides malicious SQL statements through the application. 
10206 | 
10207 | How to prevent:
10208 | * **Prepared statements with parameterized queries**
10209 | * **Stored procedures**
10210 | * **Input validation** - blacklist validation and whitelist validation
10211 | * **Principle of least privilege** - Application accounts shouldn’t assign DBA or admin type access onto the database server. This ensures that if an application is compromised, an attacker won’t have the rights to the database through the compromised application.
10212 | 
10213 | **Source:** _https://www.synopsys.com_
10214 | 
10215 | #### Q46: What is impersonation? ⭐⭐
10216 | **Answer:**
10217 | Impersonation is an act of pretending to be another person. For IT Systems impersonation means that some specific users (usually Admins) could get an access to other user's data. 
10218 | 
10219 | #### Q47: What is Cross Site Scripting (XSS)? ⭐⭐
10220 | **Answer:**
10221 | By using **Cross Site Scripting (XSS)** technique, users executed malicious scripts (also called payloads) unintentionally by clicking on untrusted links and hence, these scripts pass cookies information to attackers.
10222 | 
10223 | **Source:** _allabouttesting.org_
10224 | 
10225 | #### Q48: What is ClickJacking? ⭐⭐⭐
10226 | **Answer:**
10227 | **ClickJacking** is an attack that fools users into thinking they are clicking on one thing when they are actually clicking on another. The attack is possible thanks to HTML frames (iframes). 
10228 | 
10229 | Its other name, user interface (UI) redressing, better describes what is going on. Users think they are using a web page’s normal UI, but in fact there is a hidden UI in control; in other words, the UI has been redressed. When users click something they think is safe, the hidden UI performs a different action.
10230 | 
10231 | **Source:** _synopsys.com_
10232 | 
10233 | ## [[⬆]](#toc) <a name=50SeniorJavaDeveloperInterviewQuestionsToAskin2020>50 Senior Java Developer Interview Questions To Ask in 2020</a>
10234 | > Originally published on 👉 <a href='https://www.fullstack.cafe\blog\senior-java-developer-interview-questions'>50 Senior Java Developer Interview Questions To Ask in 2020 | FullStack.Cafe</a>
10235 | 
10236 | #### Q1: What is Builder pattern? ⭐⭐
10237 | **Answer:**
10238 | *Builder pattern* builds a complex object using simple objects and using a step by step approach. This builder is independent of other objects.
10239 | 
10240 | 
10241 | <div class="text-center"/>
10242 | <img src="https://www.plantuml.com/plantuml/svg/TOux3i8m343tdC9ZE_G234YqIAo86mJ7WqMQLeupS7kSqY90iCJsU_4dtpZDNlm8MU-Hx1L6BMDqHfMHPvyK_12PQio0d-B8GgYJL1M-UgQ4GafzuHXe-O5NvunvfPeYTDtU4jZ14sukh2gy6LXhcset5jIcTG6s_cN7sROVcXP-yVuF7oh75p-HNYYNQDCV" class="img-fluid" style="max-width: 500px" />
10243 | </div>
10244 | 
10245 | *The Director* class is optional and is used to make sure that the building steps are executed in the *right order* with the right data by the right builder. It's about validation and delegation.
10246 | 
10247 | Builder/Director pattern's steps invocations could be semantically presented by *method chaining* or so called *Fluent Interface* syntax. 
10248 | 
10249 | ```js
10250 | Pizza pizza = new Pizza.Builder()
10251 |                        .cheese(true)
10252 |                        .pepperoni(true)
10253 |                        .bacon(true)
10254 |                        .build();
10255 | ```
10256 | 
10257 | **Source:** _tutorialspoint.com_
10258 | 
10259 | #### Q2: What is Adapter Pattern? ⭐⭐⭐
10260 | **Answer:**
10261 | *Adapter pattern* works as a bridge between two incompatible interfaces. This pattern involves a single class which is responsible to join functionalities of independent or incompatible interfaces (adaptees).
10262 | 
10263 | <div class="text-center"/>
10264 | <img src="http://www.java2novice.com/images/ObjectAdapter.png" class="img-fluid" style="max-width: 500px" />
10265 | </div>
10266 | </br>
10267 | A real life example could be a case of card reader which acts as an adapter between memory card and a laptop. You plugin the memory card into card reader and card reader into the laptop so that memory card can be read via laptop.
10268 | 
10269 | **Source:** _tutorialspoint.com_
10270 | 
10271 | #### Q3: What is Facade pattern? ⭐⭐⭐
10272 | **Answer:**
10273 | **Facade pattern** hides the complexities of the system and provides an interface to the client using which the client can access the system. This type of design pattern comes under *structural pattern* as this pattern adds an interface to existing system to hide its complexities.
10274 | 
10275 | <img src="https://upload.wikimedia.org/wikipedia/en/5/57/Example_of_Facade_design_pattern_in_UML.png" class="image-fluid"/>
10276 | 
10277 | This pattern involves a single class which provides simplified methods required by client and delegates calls to methods of existing system classes.
10278 | 
10279 | **Source:** _tutorialspoint.com_
10280 | 
10281 | #### Q4: What is the function of CI (Continuous Integration) server? ⭐⭐
10282 | **Answer:**
10283 | CI server function is to continuously integrate all changes being made and committed to repository by different developers and check for compile errors. It needs to build code several times a day, preferably after every commit so it can detect which commit made the breakage if the breakage happens.
10284 | 
10285 | **Source:** _linoxide.com_
10286 | 
10287 | #### Q5: What are the differences between continuous integration, continuous delivery, and continuous deployment? ⭐⭐⭐
10288 | **Answer:**
10289 | * Developers practicing **continuous integration** merge their changes back to the main branch as often as possible. By doing so, you avoid the integration hell that usually happens when people wait for release day to merge their changes into the release branch.
10290 | * **Continuous delivery** is an extension of continuous integration to make sure that you can release new changes to your customers quickly in a sustainable way. This means that on top of having automated your testing, you also have automated your release process and you can deploy your application at any point of time by clicking on a button.
10291 | * **Continuous deployment** goes one step further than continuous delivery. With this practice, every change that passes all stages of your production pipeline is released to your customers. There's no human intervention, and only a failed test will prevent a new change to be deployed to production.
10292 | 
10293 | **Source:** _atlassian.com_
10294 | 
10295 | #### Q6: What is JVM? Why is Java called the “Platform Independent Programming Language”?  ⭐
10296 | **Answer:**
10297 | A Java virtual machine (JVM) is a process virtual machine that can execute Java bytecode. Each Java source file is compiled into a bytecode file, which is executed by the JVM. Java was designed to allow application programs to be built that could be run on any platform, without having to be rewritten or recompiled by the programmer for each separate platform. A Java virtual machine makes this possible, because it is aware of the specific instruction lengths and other particularities of the underlying hardware platform.
10298 | 
10299 | **Source:** _github.com/snowdream_
10300 | 
10301 | #### Q7: What is the Difference between JDK and JRE?  ⭐
10302 | **Answer:**
10303 | * **The Java Runtime Environment (JRE) **is basically the Java Virtual Machine (**JVM**) where your Java programs are being executed. It also includes browser plugins for applet execution. 
10304 | 
10305 | * **The Java Development Kit (JDK)** is the full featured Software Development Kit for Java, including the JRE, the compilers and tools (like JavaDoc, and Java Debugger), in order for a user to develop, compile and execute Java applications.
10306 | 
10307 | **Source:** _github.com/snowdream_
10308 | 
10309 | #### Q8: What does System.gc() and Runtime.gc() methods do? ⭐⭐
10310 | **Answer:**
10311 | These methods can be used as a hint to the JVM, in order to start a garbage collection. However, this it is up to the Java Virtual Machine (JVM) to start the garbage collection immediately or later in time.
10312 | 
10313 | 
10314 | **Source:** _github.com/snowdream_
10315 | 
10316 | #### Q9: What is JDBC? ⭐⭐
10317 | **Answer:**
10318 | JDBC is an abstraction layer that allows users to choose between databases. [JDBC enables developers to write database applications in Java](http://www.javacodegeeks.com/2014/03/java-8-friday-java-8-will-revolutionize-database-access.html), without having to concern themselves with the underlying details of a particular database.
10319 | 
10320 | **Source:** _github.com/snowdream_
10321 | 
10322 | #### Q10: What is reflection and why is it useful? ⭐⭐
10323 | **Answer:**
10324 | The name **reflection** is used to describe code which is able to inspect other code in the same system (or itself) and to make modifications at runtime.
10325 | 
10326 | For example, say you have an object of an unknown type in Java, and you would like to call a 'doSomething' method on it if one exists. Java's static typing system isn't really designed to support this unless the object conforms to a known interface, but using reflection, your code can look at the object and find out if it has a method called 'doSomething' and then call it if you want to.
10327 | 
10328 | ```java
10329 | Method method = foo.getClass().getMethod("doSomething", null);
10330 | method.invoke(foo, null);
10331 | ```
10332 | 
10333 | **Source:** _stackoverflow.com_
10334 | 
10335 | #### Q11: What is difference between fail-fast and fail-safe?  ⭐⭐⭐
10336 | **Answer:**
10337 | The [Iterator's](http://docs.oracle.com/javase/7/docs/api/java/util/Iterator.html)  fail-safe property works with the clone of the underlying collection and thus, it is not affected by any modification in the collection. All the collection classes in java.util package are fail-fast, while the collection classes in java.util.concurrent are fail-safe. Fail-fast iterators throw a [ConcurrentModificationException](http://examples.javacodegeeks.com/java-basics/exceptions/java-util-concurrentmodificationexception-how-to-handle-concurrent-modification-exception/), while fail-safe iterator never throws such an exception.
10338 | 
10339 | **Source:** _github.com/snowdream_
10340 | 
10341 | #### Q12: What is structure of Java Heap? ⭐⭐⭐
10342 | **Answer:**
10343 | The JVM has a heap that is the runtime data area from which memory for all class instances and arrays is allocated. It is created at the JVM start-up. Heap memory for objects is reclaimed by an automatic memory management system which is known as a garbage collector. Heap memory consists of live and dead objects. Live objects are accessible by the application and will not be a subject of garbage collection. Dead objects are those which will never be accessible by the application, but have not been collected by the garbage collector yet. Such objects occupy the heap memory space until they are eventually collected by the garbage collector.
10344 | 
10345 | **Source:** _github.com/snowdream_
10346 | 
10347 | #### Q13: Which Swing methods are thread-safe? ⭐⭐⭐
10348 | **Answer:**
10349 | There are only three thread-safe methods: 
10350 | * repaint, 
10351 | * revalidate,
10352 | * invalidate.
10353 | 
10354 | **Source:** _github.com/snowdream_
10355 | 
10356 | #### Q14: Is Java “pass-by-reference” or “pass-by-value”? ⭐⭐⭐
10357 | **Answer:**
10358 | Java is always **pass-by-value**. Unfortunately, when we pass the value of an object, we are passing the _reference_ to it. There is no such thing as "pass-by-reference" in Java. This is confusing to beginners.
10359 | 
10360 | The key to understanding this is that something like
10361 | ```java
10362 | Dog myDog;
10363 | ```
10364 | is not a Dog; it's actually a `pointer` to a Dog.
10365 | 
10366 | So when you have
10367 | ```java
10368 | Dog myDog = new Dog("Rover");
10369 | foo(myDog);
10370 | ```
10371 | you're essentially passing the address of the created `Dog` object to the `foo` method.
10372 | 
10373 | **Source:** _stackoverflow.com_
10374 | 
10375 | #### Q15: How do I read/convert an InputStream into a String in Java? ⭐⭐⭐
10376 | **Answer:**
10377 | A nice way to do this is using Apache commons `IOUtils` to copy the `InputStream` into a `StringWriter` like:
10378 | 
10379 | ```java
10380 | tringWriter writer = new StringWriter();
10381 | IOUtils.copy(inputStream, writer, encoding);
10382 | String theString = writer.toString();
10383 | ```
10384 | or
10385 | ```java
10386 | // NB: does not close inputStream, you'll have to use try-with-resources for that
10387 | String theString = IOUtils.toString(inputStream, encoding); 
10388 | ```
10389 | 
10390 | **Source:** _stackoverflow.com_
10391 | 
10392 | #### Q16: What is a JavaBean exactly? ⭐⭐⭐
10393 | **Answer:**
10394 | Basically, a "Bean" follows the standart:
10395 | 
10396 | * is a **serializable** object (that is, it implements `java.io.Serializable`, and does so correctly), that
10397 | * has "properties" whose getters and setters are just methods with certain names (like, say, getFoo() is the getter for the "Foo" property), and
10398 | * has a public 0-arg constructor (so it can be created at will and configured by setting its properties).
10399 | 
10400 | There is no syntactic difference between a JavaBean and another class - a class is a JavaBean if it follows the standards.
10401 | 
10402 | **Source:** _stackoverflow.com_
10403 | 
10404 | #### Q17: Can == be used on enum? ⭐⭐⭐
10405 | **Answer:**
10406 | **Yes**: enums have tight instance controls that allows you to use == to compare instances. Here's the guarantee provided by the language specification.
10407 | 
10408 | **Source:** _stackoverflow.com_
10409 | 
10410 | #### Q18: What are the differences between == and equals? ⭐⭐⭐
10411 | **Answer:**
10412 | As a reminder, it needs to be said that generally, `==` is NOT a viable alternative to `equals`. When it is, however (such as with enum), there are two important differences to consider:
10413 | 
10414 | 1. `==` never throws `NullPointerException`
10415 | 
10416 | ```java
10417 | enum Color { BLACK, WHITE };
10418 | 
10419 | Color nothing = null;
10420 | if (nothing == Color.BLACK);      // runs fine
10421 | if (nothing.equals(Color.BLACK)); // throws NullPointerEx
10422 | ```
10423 | 
10424 | 2. `==` is subject to type compatibility check at compile time
10425 | 
10426 | ```java
10427 | enum Color { BLACK, WHITE };
10428 | enum Chiral { LEFT, RIGHT };
10429 | 
10430 | if (Color.BLACK.equals(Chiral.LEFT)); // compiles fine
10431 | if (Color.BLACK == Chiral.LEFT);      // DOESN'T COMPILE!!! Incompatible types!
10432 | ```
10433 | 
10434 | **Source:** _stackoverflow.com_
10435 | 
10436 | #### Q19: Is there anything like static class in java? ⭐⭐⭐
10437 | **Answer:**
10438 | Java has **no way** of making a top-level class static but you can simulate a static class like this:
10439 | 
10440 | * Declare your class final - Prevents extension of the class since extending a static class makes no sense
10441 | * Make the constructor private - Prevents instantiation by client code as it makes no sense to instantiate a static class
10442 | * Make all the members and functions of the class static - Since the class cannot be instantiated no instance methods can be called or instance fields accessed
10443 | * Note that the compiler will not prevent you from declaring an instance (non-static) member. The issue will only show up if you attempt to call the instance member
10444 | 
10445 | **Source:** _stackoverflow.com_
10446 | 
10447 | #### Q20: What do the ... dots in the method parameters mean? ⭐⭐⭐
10448 | **Details:**
10449 | What do the 3 dots in the following method mean?
10450 | ```java
10451 | public void myMethod(String... strings){
10452 |     // method body
10453 | }
10454 | ```
10455 | 
10456 | **Answer:**
10457 | That feature is called varargs, and it's a feature introduced in Java 5. It means that function can receive multiple `String` arguments:
10458 | ```java
10459 | myMethod("foo", "bar");
10460 | myMethod("foo", "bar", "baz");
10461 | myMethod(new String[]{"foo", "var", "baz"}); // you can eve
10462 | ```
10463 | Then, you can use the `String` var as an array:
10464 | ```java
10465 | public void myMethod(String... strings){
10466 |     for(String whatever : strings){
10467 |         // do what ever you want
10468 |     }
10469 | 
10470 |     // the code above is is equivalent to
10471 |     for( int i = 0; i < strings.length; i++){
10472 |         // classical for. In this case you use strings[i]
10473 |     }
10474 | }
10475 | ```
10476 | 
10477 | **Source:** _stackoverflow.com_
10478 | 
10479 | #### Q21: What is the JIT? ⭐⭐⭐
10480 | **Answer:**
10481 | The **JIT** is the JVM’s mechanism by which it can optimize code at runtime.
10482 | 
10483 | JIT means **Just In Time**. It is a central feature of any JVM. Among other optimizations, it can perform code inlining, lock coarsening or lock eliding, escape analysis etc.
10484 | 
10485 | The main benefit of the JIT is on the programmer’s side: code should be written so that it just works; if the code can be optimized at runtime, more often than not, the JIT will find a way.
10486 | 
10487 | **Source:** _codementor.io_
10488 | 
10489 | #### Q22: What is the volatile keyword useful for? ⭐⭐⭐
10490 | **Answer:**
10491 | `volatile` has semantics for memory visibility. Basically, the value of a volatile field becomes visible to all readers (other threads in particular) after a write operation completes on it. Without volatile, readers could see some non-updated value.
10492 | 
10493 | **Source:** _stackoverflow.com_
10494 | 
10495 | #### Q23: Compare the sleep() and wait() methods in Java ⭐⭐⭐
10496 | **Answer:**
10497 | * `sleep()` is a blocking operation that keeps a hold on the monitor / lock of the shared object for the specified number of milliseconds.
10498 | 
10499 | * `wait()`, on the other hand, simply pauses the thread until either (a) the specified number of milliseconds have elapsed or (b) it receives a desired notification from another thread (whichever is first), without keeping a hold on the monitor/lock of the shared object.
10500 | 
10501 | `sleep()` is most commonly used for polling, or to check for certain results, at a regular interval. `wait()` is generally used in multithreaded applications, in conjunction with `notify() / notifyAll()`, to achieve synchronization and avoid race conditions.
10502 | 
10503 | **Source:** _toptal.com_
10504 | 
10505 | #### Q24: What is the difference between Serial and Throughput Garbage collector? ⭐⭐⭐⭐
10506 | **Answer:**
10507 | Read Full Answer on 👉 <a href='https://www.fullstack.cafe\blog\senior-java-developer-interview-questions'>FullStack.Cafe</a>
10508 | 
10509 | #### Q25: What is RMI? ⭐⭐⭐⭐
10510 | **Answer:**
10511 | Read Full Answer on 👉 <a href='https://www.fullstack.cafe\blog\senior-java-developer-interview-questions'>FullStack.Cafe</a>
10512 | 
10513 | #### Q26: Why is Spring MVC better than Servlets / JSP ? ⭐⭐⭐⭐
10514 | **Answer:**
10515 | Read Full Answer on 👉 <a href='https://www.fullstack.cafe\blog\senior-java-developer-interview-questions'>FullStack.Cafe</a>
10516 | 
10517 | #### Q27: Why is char[] preferred over String for passwords? ⭐⭐⭐⭐
10518 | **Details:**
10519 | Why does `String` pose a threat to security when it comes to passwords? It feels inconvenient to use `char[]`?
10520 | 
10521 | **Answer:**
10522 | Read Full Answer on 👉 <a href='https://www.fullstack.cafe\blog\senior-java-developer-interview-questions'>FullStack.Cafe</a>
10523 | 
10524 | #### Q28: What is Double Brace initialization in Java? ⭐⭐⭐⭐
10525 | **Answer:**
10526 | Read Full Answer on 👉 <a href='https://www.fullstack.cafe\blog\senior-java-developer-interview-questions'>FullStack.Cafe</a>
10527 | 
10528 | #### Q29: Explain a use case for the Builder Design Pattern ⭐⭐⭐⭐
10529 | **Answer:**
10530 | Read Full Answer on 👉 <a href='https://www.fullstack.cafe\blog\senior-java-developer-interview-questions'>FullStack.Cafe</a>
10531 | 
10532 | #### Q30: Is null check needed before calling instanceof? ⭐⭐⭐⭐
10533 | **Details:**
10534 | Will 
10535 | 
10536 | ```java
10537 | null instanceof SomeClass
10538 | ```
10539 | return `false` or throw a `NullPointerException`?
10540 | 
10541 | **Answer:**
10542 | Read Full Answer on 👉 <a href='https://www.fullstack.cafe\blog\senior-java-developer-interview-questions'>FullStack.Cafe</a>
10543 | 
10544 | #### Q31: What does 'synchronized' mean? ⭐⭐⭐⭐⭐
10545 | **Answer:**
10546 | Read Full Answer on 👉 <a href='https://www.fullstack.cafe\blog\senior-java-developer-interview-questions'>FullStack.Cafe</a>
10547 | 
10548 | #### Q32: What's wrong with Double Brace initialization in Java? ⭐⭐⭐⭐⭐
10549 | **Answer:**
10550 | Read Full Answer on 👉 <a href='https://www.fullstack.cafe\blog\senior-java-developer-interview-questions'>FullStack.Cafe</a>
10551 | 
10552 | #### Q33: Provide some examples when a finally block won't be executed in Java? ⭐⭐⭐⭐⭐
10553 | **Answer:**
10554 | Read Full Answer on 👉 <a href='https://www.fullstack.cafe\blog\senior-java-developer-interview-questions'>FullStack.Cafe</a>
10555 | 
10556 | #### Q34: Explain what will the code return ⭐⭐⭐⭐⭐
10557 | **Details:**
10558 | Consider:
10559 | ```java
10560 | try { return true; } finally { return false; }
10561 | ```
10562 | 
10563 | **Answer:**
10564 | Read Full Answer on 👉 <a href='https://www.fullstack.cafe\blog\senior-java-developer-interview-questions'>FullStack.Cafe</a>
10565 | 
10566 | #### Q35: What is an efficient way to implement a singleton pattern in Java? ⭐⭐⭐⭐⭐
10567 | **Answer:**
10568 | Read Full Answer on 👉 <a href='https://www.fullstack.cafe\blog\senior-java-developer-interview-questions'>FullStack.Cafe</a>
10569 | 
10570 | #### Q36: What's the difference between SoftReference and WeakReference in Java? ⭐⭐⭐⭐⭐
10571 | **Answer:**
10572 | Read Full Answer on 👉 <a href='https://www.fullstack.cafe\blog\senior-java-developer-interview-questions'>FullStack.Cafe</a>
10573 | 
10574 | #### Q37: Compare volatile vs static variables in Java ⭐⭐⭐⭐⭐
10575 | **Answer:**
10576 | Read Full Answer on 👉 <a href='https://www.fullstack.cafe\blog\senior-java-developer-interview-questions'>FullStack.Cafe</a>
10577 | 
10578 | #### Q38: What are the pros and cons of Microservice Architecture? ⭐⭐⭐⭐
10579 | **Answer:**
10580 | Read Full Answer on 👉 <a href='https://www.fullstack.cafe\blog\senior-java-developer-interview-questions'>FullStack.Cafe</a>
10581 | 
10582 | #### Q39: What is Materialized View pattern and when will you use it? ⭐⭐⭐⭐
10583 | **Answer:**
10584 | Read Full Answer on 👉 <a href='https://www.fullstack.cafe\blog\senior-java-developer-interview-questions'>FullStack.Cafe</a>
10585 | 
10586 | #### Q40: What is the relationship between a class and an object? ⭐⭐
10587 | **Answer:**
10588 | A class acts as a blue-print that defines the properties, states, and behaviors that are common to a number of objects. An object is an instance of the class. For example, you have a class called _Vehicle_ and _Car_ is the object of that class. You can create any number of objects for the class named _Vehicle_, such as _Van_, _Truck_, and _Auto_.  
10589 |       
10590 | The _new_ operator is used to create an object of a class. When an object of a class is instantiated, the system allocates memory for every data member that is present in the class.
10591 | 
10592 | **Source:** _indiabix.com_
10593 | 
10594 | #### Q41: State the features of an interface. ⭐⭐⭐
10595 | **Answer:**
10596 | An interface is a template that contains only the signature of methods. The signature of a method consists of the numbers of parameters, the type of parameter (value, reference, or output), and the order of parameters. An interface has no implementation on its own because it contains only the definition of methods without any method body. An interface is defined using the _interface_ keyword. Moreover, you cannot instantiate an interface. The various features of an interface are as follows:  
10597 | 
10598 | *   An interface is used to implement multiple inheritance in code. This feature of an interface is quite different from that of abstract classes because a class cannot derive the features of more than one class but can easily implement multiple interfaces.
10599 | *   It defines a specific set of methods and their arguments.
10600 | *   Variables in interface must be declared as _public_, _static_, and _final_ while methods must be _public_ and _abstract_.
10601 | *   A class implementing an interface must implement all of its methods.
10602 | *   An interface can derive from more than one interface.
10603 | 
10604 | **Source:** _indiabix.com_
10605 | 
10606 | #### Q42: What is Coupling in OOP? ⭐⭐⭐⭐
10607 | **Answer:**
10608 | Read Full Answer on 👉 <a href='https://www.fullstack.cafe\blog\senior-java-developer-interview-questions'>FullStack.Cafe</a>
10609 | 
10610 | #### Q43: What is Spring? ⭐
10611 | **Answer:**
10612 | **Spring** is an open source development framework for enterprise Java. The core features of the Spring Framework can be used in developing any Java application, but there are extensions for building web applications on top of the Java EE platform. Spring framework targets to make J2EE development easier to use and promote good programming practice by enabling a POJO-based (Plain Old Java Object) programming model.
10613 | 
10614 | **Source:** _tutorialspoint.com_
10615 | 
10616 | #### Q44: What are benefits of using Spring? ⭐⭐
10617 | **Answer:**
10618 | Following is the list of few of the great benefits of using Spring Framework:
10619 | *   **Lightweight** − Spring is lightweight when it comes to size and transparency. The basic version of spring framework is around 2MB.
10620 | *   **Inversion of control (IOC)** − Loose coupling is achieved in spring using the technique Inversion of Control. The objects give their dependencies instead of creating or looking for dependent objects.
10621 | *   **Aspect oriented (AOP)** − Spring supports Aspect oriented programming and enables cohesive development by separating application business logic from system services.
10622 | *   **Container** − Spring contains and manages the life cycle and configuration of application objects.
10623 | *   **MVC Framework** − Spring's web framework is a well-designed web MVC framework, which provides a great alternative to web frameworks such as Struts or other over-engineered or less popular web frameworks.
10624 | *   **Transaction Management** − Spring provides a consistent transaction management interface that can scale down to a local transaction (using a single database, for example) and scale up to global transactions (using JTA, for example).
10625 | *   **Exception Handling** − Spring provides a convenient API to translate technology-specific exceptions (thrown by JDBC, Hibernate, or JDO, for example) into consistent, unchecked exceptions.
10626 | 
10627 | **Source:** _tutorialspoint.com_
10628 | 
10629 | #### Q45: What are Spring beans? ⭐⭐
10630 | **Answer:**
10631 | The objects that form the backbone of your application and that are managed by the Spring IoC container are called **beans**. A bean is an object that is instantiated, assembled, and otherwise managed by a Spring IoC container. These beans are created with the configuration metadata that you supply to the container, for example, in the form of XML `<bean/>` definitions.
10632 | 
10633 | **Source:** _tutorialspoint.com_
10634 | 
10635 | #### Q46: What is Application Context? ⭐⭐
10636 | **Answer:**
10637 | On the surface, an application context is the same as a bean factory. Both load bean definitions, wire beans together, and dispense beans upon request. But it also provides:
10638 | 
10639 | *   A means for resolving text messages, including support for internationalization
10640 | *   A generic way to load file resources
10641 | *   Events to beans that are registered as listeners
10642 | 
10643 | **Source:** _developersbook.com_
10644 | 
10645 | #### Q47: What is Spring IoC container? ⭐⭐⭐
10646 | **Answer:**
10647 | The Spring IoC creates the objects, wire them together, configure them, and manage their complete lifecycle from creation till destruction. The Spring container uses dependency injection (DI) to manage the components that make up an application.
10648 | 
10649 | There are two types of IoC containers in Spring:
10650 | 
10651 | *   **Bean Factory container** − This is the simplest container providing basic support for DI .The BeanFactory is usually preferred where the resources are limited like mobile devices or applet based applications
10652 | *   **Spring ApplicationContext Container** − This container adds more enterprise-specific functionality such as the ability to resolve textual messages from a properties file and the ability to publish application events to interested event listeners.
10653 | 
10654 | **Source:** _tutorialspoint.com_
10655 | 
10656 | #### Q48: What is Controller in Spring MVC framework? ⭐⭐⭐
10657 | **Answer:**
10658 | **Controllers** provide access to the application behavior that you typically define through a service interface. Controllers interpret user input and transform it into a model that is represented to the user by the view. Spring implements a controller in a very abstract way, which enables you to create a wide variety of controllers.
10659 | 
10660 | **Source:** _tutorialspoint.com_
10661 | 
10662 | #### Q49: Does Spring Bean provide thread safety? ⭐⭐⭐
10663 | **Answer:**
10664 | The default scope of Spring bean is singleton, so there will be only one instance per context. That means that all the having a class level variable that any thread can update will lead to inconsistent data. Hence in default mode spring beans are not thread-safe.
10665 |     
10666 | However, we can change spring bean scope to request, prototype or session to achieve thread-safety at the cost of performance. It’s a design decision and based on the project requirements.
10667 | 
10668 | **Source:** _journaldev.com_
10669 | 
10670 | #### Q50: What is the difference between concern and cross-cutting concern in Spring AOP? ⭐⭐⭐⭐
10671 | **Answer:**
10672 | Read Full Answer on 👉 <a href='https://www.fullstack.cafe\blog\senior-java-developer-interview-questions'>FullStack.Cafe</a>
10673 | 
10674 | ## [[⬆]](#toc) <a name=6WebSecurityInterviewQuestionsforFullStackDevelopers>6 Web Security Interview Questions for Full Stack Developers</a>
10675 | > Originally published on 👉 <a href='https://www.fullstack.cafe\blog\6-web-security-interview-questions-for-fullstack-developers'>6 Web Security Interview Questions for Full Stack Developers | FullStack.Cafe</a>
10676 | 
10677 | #### Q1: How to mitigate the SQL Injection risks? ⭐⭐
10678 | **Answer:**
10679 | To mitigate SQL injection:
10680 | 
10681 | *   **Prepared Statements with Parameterized Queries:** Always ensure that your SQL interpreter always able to differentiate between code and data. Never use dynamic queries which fail to find the difference between code and data. Instead, use static SQL query and then pass in the external input as a parameter to query.  Use of Prepared Statements (with Parameterized Queries) force developer to first define all the SQL code, and then pass in each parameter to the query later.
10682 | *   **Use of Stored Procedures:** Stored Procedure is like a function in C where database administrator call it whenever he/she need it. It is not completely mitigated SQL injection but definitely helps in reducing risks of SQL injection by avoiding dynamic SQL generation inside.
10683 | *   **White List Input Validation:** Always use white list input validation and allow only preapproved input by the developer. Never use blacklist approach as it is less secure than whitelist approach.
10684 | *   **Escaping All User Supplied Input**
10685 | *   **Enforcing Least Privilege**
10686 | 
10687 | **Source:** _career.guru99.com_
10688 | 
10689 | #### Q2: What is Cross Site Scripting (XSS)? ⭐⭐
10690 | **Answer:**
10691 | By using **Cross Site Scripting (XSS)** technique, users executed malicious scripts (also called payloads) unintentionally by clicking on untrusted links and hence, these scripts pass cookies information to attackers.
10692 | 
10693 | **Source:** _allabouttesting.org_
10694 | 
10695 | #### Q3: What is ClickJacking? ⭐⭐⭐
10696 | **Answer:**
10697 | **ClickJacking** is an attack that fools users into thinking they are clicking on one thing when they are actually clicking on another. The attack is possible thanks to HTML frames (iframes). 
10698 | 
10699 | Its other name, user interface (UI) redressing, better describes what is going on. Users think they are using a web page’s normal UI, but in fact there is a hidden UI in control; in other words, the UI has been redressed. When users click something they think is safe, the hidden UI performs a different action.
10700 | 
10701 | **Source:** _synopsys.com_
10702 | 
10703 | #### Q4: List the attributes of Security Testing ⭐⭐⭐
10704 | **Answer:**
10705 | 
10706 | **Security testing** is to be carried out to make sure that whether the system prevents the unauthorized user to access the resource and data. Security Testing needs to cover the seven attributes of Security Testing: 
10707 | 
10708 | * **Authentication** - Authentication is a process of identifying the person before accessing the system. It allows user to access the system information only if authentication check got passed.
10709 | * **Authorization** - Once the Authentication passed the Authorization comes in the picture to limit the user as per the permission set for the user.
10710 | * **Confidentiality** - Confidentiality is to be carried out to check if unauthorized user and less privileged users are not able to access the information. It is to check that the protection of information and resources from the users other than the authorized and authenticated. 
10711 | * **Availability** - The availability of system is to check the system is available for authorized users whenever they want to use except for the maintenance window & upgrade for security patches.
10712 | * **Integrity** - Integrity is to make sure that the information received is not altered during the transit & check if correct information presented to user is as per the user groups, privileges & restrictions.
10713 | * **Non-repudiation** - Nonrepudiation is the assurance that someone cannot deny something. For security testing it is tracking who is accessing the systems and which of the requests were denied along with additional details like the Timestamp and the IP address from where the requests came from. 
10714 | * **Resilience** - Resilience is to check the system is resistance to bear the attacks, this can be implemented using encryption, use OTP (One Time Password), two layer authentication or RSA key token.
10715 | 
10716 | **Source:** _softwaretestingclass.com_
10717 | 
10718 | #### Q5: What are the types of XSS? ⭐⭐⭐⭐
10719 | **Answer:**
10720 | Read Full Answer on 👉 <a href='https://www.fullstack.cafe\blog\6-web-security-interview-questions-for-fullstack-developers'>FullStack.Cafe</a>
10721 | 
10722 | #### Q6: What is HSTS? ⭐⭐⭐⭐
10723 | **Answer:**
10724 | Read Full Answer on 👉 <a href='https://www.fullstack.cafe\blog\6-web-security-interview-questions-for-fullstack-developers'>FullStack.Cafe</a>
10725 | 
10726 | ## [[⬆]](#toc) <a name=60JavaandSpringInterviewQuestionsYouMustKnow>60 Java and Spring Interview Questions You Must Know</a>
10727 | > Originally published on 👉 <a href='https://www.fullstack.cafe\blog\java-spring-interview-questions'>60 Java and Spring Interview Questions You Must Know | FullStack.Cafe</a>
10728 | 
10729 | #### Q1: What is Circular Queue and why will you use one? ⭐⭐⭐
10730 | **Answer:**
10731 | **Circular Queue** is a *linear data structure* in which the operations are performed based on FIFO (First In First Out) principle and the last position is connected back to the first position to make a circle. It is also called *Ring Buffer*. Circular queue avoids the *wastage of space* in a regular queue implementation using arrays.
10732 | 
10733 | **Source:** _programiz.com_
10734 | 
10735 | #### Q2: What does “program to interfaces, not implementations” mean? ⭐⭐⭐
10736 | **Answer:**
10737 | *Coding against interface* means, the client code always holds an Interface object which is supplied by a *factory*. 
10738 | 
10739 | Any instance returned by the factory would be of type Interface which any factory candidate class must have implemented. This way the client program is not worried about implementation and the interface signature determines what all operations can be done. 
10740 | 
10741 | This approach can be used to change the behavior of a program at run-time. It also helps you to write far better programs from the maintenance point of view.
10742 | 
10743 | **Source:** _tutorialspoint.com_
10744 | 
10745 | #### Q3: What is Observer pattern? ⭐⭐⭐
10746 | **Answer:**
10747 | **Observer pattern**  (also known as *Publish-Subscribe Pattern*) is used when there is one-to-many relationship between objects such as if one object is modified, its dependent objects are to be notified automatically. Observer pattern falls under _behavioral_ pattern category.
10748 | 
10749 | An object with a one-to-many relationship with other objects who are interested in its state is called the _subject_ or _publisher_. The _observers_ are notified whenever the state of the _subject_ changes and can act accordingly. The _subject_ can have any number of dependent _observers_ which it notifies, and any number of _observers_ can subscribe to the _subject_ to receive such notifications.
10750 | 
10751 | Observer pattern uses two actor classes:
10752 | * The Observer (os Subscriber) abstract class provides an `update()` method which will be called by the subject to notify it of the subject’s state change. 
10753 | * The Subject (or Publisher) class is also an abstract class and defines four primary methods: `attach()`, `detach()`, `setState()`, and `notify()`
10754 | 
10755 | 
10756 | 
10757 | <div class="text-center">
10758 | <img src="https://upload.wikimedia.org/wikipedia/commons/0/01/W3sDesign_Observer_Design_Pattern_UML.jpg" class="img-fluid"/>
10759 | </div>
10760 | 
10761 | **Source:** _sitepoint.com_
10762 | 
10763 | #### Q4: What's the difference between the Dependency Injection and Service Locator patterns? ⭐⭐⭐⭐⭐
10764 | **Answer:**
10765 | Read Full Answer on 👉 <a href='https://www.fullstack.cafe\blog\java-spring-interview-questions'>FullStack.Cafe</a>
10766 | 
10767 | #### Q5: What is the Difference between JDK and JRE?  ⭐
10768 | **Answer:**
10769 | * **The Java Runtime Environment (JRE) **is basically the Java Virtual Machine (**JVM**) where your Java programs are being executed. It also includes browser plugins for applet execution. 
10770 | 
10771 | * **The Java Development Kit (JDK)** is the full featured Software Development Kit for Java, including the JRE, the compilers and tools (like JavaDoc, and Java Debugger), in order for a user to develop, compile and execute Java applications.
10772 | 
10773 | **Source:** _github.com/snowdream_
10774 | 
10775 | #### Q6: What is the difference between an Applet and a Java Application? ⭐
10776 | **Answer:**
10777 | * Applets are executed within a Java enabled browser, but a 
10778 | * Java application is a standalone Java program that can be executed outside of a browser. 
10779 | 
10780 | However, they both require the existence of a Java Virtual Machine (JVM). Furthermore, a Java application requires a main method with a specific signature, in order to start its execution. Java applets don’t need such a method to start their execution. Finally, Java applets typically use a restrictive security policy, while Java applications usually use more relaxed security policies.
10781 | 
10782 | **Source:** _github.com/snowdream_
10783 | 
10784 | #### Q7: What is a JSP Page? ⭐
10785 | **Answer:**
10786 | A **Java Server Page (JSP)** is a text document that contains two types of text: 
10787 | * static data and 
10788 | * JSP elements. 
10789 | 
10790 | Static data can be expressed in any text-based format, such as HTML or XML. JSP is a technology that mixes static content with dynamically-generated content.
10791 | 
10792 | **Source:** _github.com/snowdream_
10793 | 
10794 | #### Q8: What is a Servlet? ⭐
10795 | **Answer:**
10796 | The servlet is a Java programming language class used to process client requests and generate dynamic web content. Servlets are mostly used to process or store data submitted by an HTML form, provide dynamic content and manage state information that does not exist in the stateless HTTP protocol.
10797 | 
10798 | **Source:** _github.com/snowdream_
10799 | 
10800 | #### Q9: What are pass by reference and pass by value?  ⭐⭐
10801 | **Answer:**
10802 | * When an object is **passed by value**, this means that a copy of the object is passed. Thus, even if changes are made to that object, it doesn’t affect the original value. 
10803 | * When an object is **passed by reference**, this means that the actual object is not passed, rather a reference of the object is passed. Thus, any changes made by the external method, are also reflected in all places.
10804 | 
10805 | **Source:** _github.com/snowdream_
10806 | 
10807 | #### Q10: What are the basic interfaces of Java Collections Framework?  ⭐⭐
10808 | **Answer:**
10809 | **Java Collections Framework** provides a well designed set of interfaces and classes that support operations on a collections of objects. The most basic interfaces that reside in the Java Collections Framework are:
10810 | 
10811 | * **Collection**, which represents a group of objects known as its elements.
10812 | * **Set**, which is a collection that cannot contain duplicate elements.
10813 | * **List**, which is an ordered collection and can contain duplicate elements.
10814 | * **Map**,  which is an object that maps keys to values and cannot contain duplicate keys.
10815 | 
10816 | **Source:** _github.com/snowdream_
10817 | 
10818 | #### Q11: What differences exist between HashMap and Hashtable?  ⭐⭐
10819 | **Answer:**
10820 | There are several differences between `HashMap` and `Hashtable` in Java:
10821 | 
10822 |  1. `Hashtable` is synchronized, whereas `HashMap` is not. This makes `HashMap` better for non-threaded applications, as unsynchronized Objects typically perform better than synchronized ones.
10823 | 
10824 |  2. `Hashtable` does not allow `null` keys or values.  `HashMap` allows one `null` key and any number of `null` values.
10825 | 
10826 |  3. One of HashMap's subclasses is `LinkedHashMap`, so in the event that you'd want predictable iteration order (which is insertion order by default), you could easily swap out the `HashMap` for a `LinkedHashMap`.  This wouldn't be as easy if you were using `Hashtable`.
10827 | 
10828 | **Source:** _stackoverflow.com_
10829 | 
10830 | #### Q12: What does System.gc() and Runtime.gc() methods do? ⭐⭐
10831 | **Answer:**
10832 | These methods can be used as a hint to the JVM, in order to start a garbage collection. However, this it is up to the Java Virtual Machine (JVM) to start the garbage collection immediately or later in time.
10833 | 
10834 | 
10835 | **Source:** _github.com/snowdream_
10836 | 
10837 | #### Q13: What is the difference between Exception and Error in java? ⭐⭐
10838 | **Answer:**
10839 | * An **Error** "indicates serious problems that a reasonable application should not try to catch."
10840 | * An **Exception** "indicates conditions that a reasonable application might want to catch."
10841 | 
10842 | **Source:** _github.com/snowdream_
10843 | 
10844 | #### Q14: What is an Java Applet? ⭐⭐
10845 | **Answer:**
10846 | A Java Applet is program that can be included in a HTML page and be executed in a java enabled client browser. Applets are used for creating dynamic and interactive web applications.
10847 | 
10848 | **Source:** _github.com/snowdream_
10849 | 
10850 | #### Q15: What is JDBC? ⭐⭐
10851 | **Answer:**
10852 | JDBC is an abstraction layer that allows users to choose between databases. [JDBC enables developers to write database applications in Java](http://www.javacodegeeks.com/2014/03/java-8-friday-java-8-will-revolutionize-database-access.html), without having to concern themselves with the underlying details of a particular database.
10853 | 
10854 | **Source:** _github.com/snowdream_
10855 | 
10856 | #### Q16: How are the JSP requests handled? ⭐⭐
10857 | **Answer:**
10858 | On the arrival of a JSP request, the browser first requests a page with a .jsp extension. Then, the Web server reads the request and using the JSP compiler, the Web server converts the JSP page into a servlet class. Notice that the JSP file is compiled only on the first request of the page, or if the JSP file has changed.The generated servlet class is invoked, in order to handle the browser’s request. Once the execution of the request is over, the servlet sends a response back to the client. See [how to get Request parameters in a JSP](http://examples.javacodegeeks.com/enterprise-java/jsp/get-request-parameter-in-jsp-page/).
10859 | 
10860 | **Source:** _github.com/snowdream_
10861 | 
10862 | #### Q17: What are Decalarations? ⭐⭐
10863 | **Answer:**
10864 | Declarations are similar to variable declarations in Java. Declarations are used to declare variables for subsequent use in expressions or scriptlets. To add a declaration, you must use the sequences to enclose your declarations.
10865 | 
10866 | **Source:** _github.com/snowdream_
10867 | 
10868 | #### Q18: Can you access non static variable in static context? ⭐⭐⭐
10869 | **Answer:**
10870 | A static variable in Java belongs to its class and its value remains the same for all its instances. A static variable is initialized when the class is loaded by the JVM. If your code tries to access a non-static variable, without any instance, the compiler will complain, because those variables are not created yet and they are not associated with any instance.
10871 | 
10872 | **Source:** _github.com/snowdream_
10873 | 
10874 | #### Q19: Does Java support multiple inheritance?  ⭐⭐⭐
10875 | **Answer:**
10876 | No, Java does not support multiple inheritance. Each class is able to extend only on one class, but is able to implement more than one interfaces.
10877 | 
10878 | **Source:** _github.com/snowdream_
10879 | 
10880 | #### Q20: Explain different ways of creating a thread. Which one would you prefer and why? ⭐⭐⭐
10881 | **Answer:**
10882 | There are three ways that can be used in order for a [Thread](http://docs.oracle.com/javase/7/docs/api/java/lang/Thread.html) to be created:
10883 | 
10884 | * A class may extend the [Thread](http://docs.oracle.com/javase/7/docs/api/java/lang/Thread.html) class.
10885 | * A class may implement the [Runnable](http://docs.oracle.com/javase/7/docs/api/java/lang/Runnable.html) interface.
10886 | * An application can use the [Executor](http://docs.oracle.com/javase/7/docs/api/java/util/concurrent/Executor.html) framework, in order to create a thread pool.
10887 | 
10888 | The [Runnable](http://docs.oracle.com/javase/7/docs/api/java/lang/Runnable.html) interface is preferred, as it does not require an object to inherit the [Thread](http://docs.oracle.com/javase/7/docs/api/java/lang/Thread.html) class. In case your application design requires multiple inheritance, only interfaces can help you. Also, the thread pool is very efficient and can be implemented and used very easily.
10889 | 
10890 | **Source:** _github.com/snowdream_
10891 | 
10892 | #### Q21: What’s a deadlock?  ⭐⭐⭐
10893 | **Answer:**
10894 | A condition that occurs when [two processes are waiting for each other to complete](http://www.javacodegeeks.com/2013/01/java-deadlock-example-how-to-analyze-deadlock-situation.html), before proceeding. The result is that both processes wait endlessly.
10895 | 
10896 | **Source:** _github.com/snowdream_
10897 | 
10898 | #### Q22: What is difference between fail-fast and fail-safe?  ⭐⭐⭐
10899 | **Answer:**
10900 | The [Iterator's](http://docs.oracle.com/javase/7/docs/api/java/util/Iterator.html)  fail-safe property works with the clone of the underlying collection and thus, it is not affected by any modification in the collection. All the collection classes in java.util package are fail-fast, while the collection classes in java.util.concurrent are fail-safe. Fail-fast iterators throw a [ConcurrentModificationException](http://examples.javacodegeeks.com/java-basics/exceptions/java-util-concurrentmodificationexception-how-to-handle-concurrent-modification-exception/), while fail-safe iterator never throws such an exception.
10901 | 
10902 | **Source:** _github.com/snowdream_
10903 | 
10904 | #### Q23: What is Java Priority Queue? ⭐⭐⭐
10905 | **Answer:**
10906 | The [PriorityQueue](http://docs.oracle.com/javase/7/docs/api/java/util/PriorityQueue.html) is an unbounded queue, based on a priority heap and its elements are ordered in their natural order. At the time of its creation, we can provide a Comparator that is responsible for ordering the elements of the [PriorityQueue](http://docs.oracle.com/javase/7/docs/api/java/util/PriorityQueue.html). A [PriorityQueue](http://docs.oracle.com/javase/7/docs/api/java/util/PriorityQueue.html) doesn’t allow null values, those objects that doesn’t provide natural ordering, or those objects that don’t have any comparator associated with them. Finally, the Java [PriorityQueue](http://docs.oracle.com/javase/7/docs/api/java/util/PriorityQueue.html) is not thread-safe and it requires O(log(n)) time for its enqueing and dequeing operations.
10907 | 
10908 | **Source:** _github.com/snowdream_
10909 | 
10910 | #### Q24: When is the finalize() called? What is the purpose of finalization?  ⭐⭐⭐
10911 | **Answer:**
10912 | The finalize method is called by the garbage collector, just before releasing the object’s memory. It is normally advised to release resources held by the object inside the finalize method.
10913 | 
10914 | **Source:** _github.com/snowdream_
10915 | 
10916 | #### Q25: What is structure of Java Heap? ⭐⭐⭐
10917 | **Answer:**
10918 | The JVM has a heap that is the runtime data area from which memory for all class instances and arrays is allocated. It is created at the JVM start-up. Heap memory for objects is reclaimed by an automatic memory management system which is known as a garbage collector. Heap memory consists of live and dead objects. Live objects are accessible by the application and will not be a subject of garbage collection. Dead objects are those which will never be accessible by the application, but have not been collected by the garbage collector yet. Such objects occupy the heap memory space until they are eventually collected by the garbage collector.
10919 | 
10920 | **Source:** _github.com/snowdream_
10921 | 
10922 | #### Q26: What are the restrictions imposed on Java applets? ⭐⭐⭐
10923 | **Answer:**
10924 | Mostly due to security reasons, the following restrictions are imposed on Java applets:
10925 | 
10926 | * An applet cannot load libraries or define native methods.
10927 | * An applet cannot ordinarily read or write files on the execution host.
10928 | * An applet cannot read certain system properties.
10929 | * An applet cannot make network connections except to the host that it came from.
10930 | * An applet cannot start any program on the host that’s executing it.
10931 | 
10932 | **Source:** _github.com/snowdream_
10933 | 
10934 | #### Q27: What are Scriptlets? ⭐⭐⭐
10935 | **Answer:**
10936 | In Java Server Pages (JSP) technology, a scriptlet is a piece of Java-code embedded in a JSP page. The scriptlet is everything inside the tags. Between these tags, a user can add any valid scriplet.
10937 | 
10938 | **Source:** _github.com/snowdream_
10939 | 
10940 | #### Q28: What is the difference between a synchronized method and a synchronized block? ⭐⭐⭐⭐
10941 | **Answer:**
10942 | Read Full Answer on 👉 <a href='https://www.fullstack.cafe\blog\java-spring-interview-questions'>FullStack.Cafe</a>
10943 | 
10944 | #### Q29: How do you ensure that N threads can access N resources without deadlock?  ⭐⭐⭐⭐
10945 | **Answer:**
10946 | Read Full Answer on 👉 <a href='https://www.fullstack.cafe\blog\java-spring-interview-questions'>FullStack.Cafe</a>
10947 | 
10948 | #### Q30: What is Perm Gen space in Heap? ⭐⭐⭐⭐
10949 | **Answer:**
10950 | Read Full Answer on 👉 <a href='https://www.fullstack.cafe\blog\java-spring-interview-questions'>FullStack.Cafe</a>
10951 | 
10952 | #### Q31: What is RMI? ⭐⭐⭐⭐
10953 | **Answer:**
10954 | Read Full Answer on 👉 <a href='https://www.fullstack.cafe\blog\java-spring-interview-questions'>FullStack.Cafe</a>
10955 | 
10956 | #### Q32: What are the layers of RMI Architecture? ⭐⭐⭐⭐⭐
10957 | **Answer:**
10958 | Read Full Answer on 👉 <a href='https://www.fullstack.cafe\blog\java-spring-interview-questions'>FullStack.Cafe</a>
10959 | 
10960 | #### Q33: State the features of an interface. ⭐⭐⭐
10961 | **Answer:**
10962 | An interface is a template that contains only the signature of methods. The signature of a method consists of the numbers of parameters, the type of parameter (value, reference, or output), and the order of parameters. An interface has no implementation on its own because it contains only the definition of methods without any method body. An interface is defined using the _interface_ keyword. Moreover, you cannot instantiate an interface. The various features of an interface are as follows:  
10963 | 
10964 | *   An interface is used to implement multiple inheritance in code. This feature of an interface is quite different from that of abstract classes because a class cannot derive the features of more than one class but can easily implement multiple interfaces.
10965 | *   It defines a specific set of methods and their arguments.
10966 | *   Variables in interface must be declared as _public_, _static_, and _final_ while methods must be _public_ and _abstract_.
10967 | *   A class implementing an interface must implement all of its methods.
10968 | *   An interface can derive from more than one interface.
10969 | 
10970 | **Source:** _indiabix.com_
10971 | 
10972 | #### Q34: Explain different types of inheritance. ⭐⭐⭐⭐
10973 | **Answer:**
10974 | Read Full Answer on 👉 <a href='https://www.fullstack.cafe\blog\java-spring-interview-questions'>FullStack.Cafe</a>
10975 | 
10976 | #### Q35: What is the difference between association, aggregation and composition? ⭐⭐⭐⭐⭐
10977 | **Answer:**
10978 | Read Full Answer on 👉 <a href='https://www.fullstack.cafe\blog\java-spring-interview-questions'>FullStack.Cafe</a>
10979 | 
10980 | #### Q36: What does SOLID stand for? What are its principles? ⭐⭐⭐
10981 | **Answer:**
10982 | **S.O.L.I.D** is an acronym for the first five object-oriented design (OOD) principles by Robert C. Martin.
10983 | 
10984 | * **S** - *Single-responsiblity principle*. A class should have one and only one reason to change, meaning that a class should have only one job.
10985 | * **O** - *Open-closed principle*. Objects or entities should be open for extension, but closed for modification.
10986 | * **L** - *Liskov substitution principle*. Let q(x) be a property provable about objects of x of type T. Then q(y) should be provable for objects y of type S where S is a subtype of T.
10987 | * **I** - *Interface segregation principle*. A client should never be forced to implement an interface that it doesn't use or clients shouldn't be forced to depend on methods they do not use.
10988 | * **D** - *Dependency Inversion Principle*. Entities must depend on abstractions not on concretions. It states that the high level module must not depend on the low level module, but they should depend on abstractions.
10989 | 
10990 | **Source:** _scotch.io_
10991 | 
10992 | #### Q37: What are the DRY and DIE principles? ⭐⭐⭐
10993 | **Answer:**
10994 | In software engineering, **Don't Repeat Yourself (DRY)** or **Duplication is Evil (DIE)** is a principle of software development.
10995 | 
10996 | **Source:** _stackoverflow.com_
10997 | 
10998 | #### Q38: Is it better to return NULL or empty values from functions/methods where the return value is not present? ⭐⭐⭐
10999 | **Answer:**
11000 | Returning `null` is usually the best idea if you intend to indicate that no data is available.
11001 | 
11002 | An empty object implies data has been returned, whereas returning `null` clearly indicates that nothing has been returned.
11003 | 
11004 | Additionally, returning a `null` will result in a null exception if you attempt to access members in the object, which can be useful for highlighting buggy code - attempting to access a member of nothing makes no sense. Accessing members of an empty object will not fail meaning bugs can go undiscovered.
11005 | 
11006 | **Source:** _stackoverflow.com_
11007 | 
11008 | #### Q39: What is GOD class and why should we avoid it? ⭐⭐⭐⭐
11009 | **Answer:**
11010 | Read Full Answer on 👉 <a href='https://www.fullstack.cafe\blog\java-spring-interview-questions'>FullStack.Cafe</a>
11011 | 
11012 | #### Q40: What are benefits of using Spring? ⭐⭐
11013 | **Answer:**
11014 | Following is the list of few of the great benefits of using Spring Framework:
11015 | *   **Lightweight** − Spring is lightweight when it comes to size and transparency. The basic version of spring framework is around 2MB.
11016 | *   **Inversion of control (IOC)** − Loose coupling is achieved in spring using the technique Inversion of Control. The objects give their dependencies instead of creating or looking for dependent objects.
11017 | *   **Aspect oriented (AOP)** − Spring supports Aspect oriented programming and enables cohesive development by separating application business logic from system services.
11018 | *   **Container** − Spring contains and manages the life cycle and configuration of application objects.
11019 | *   **MVC Framework** − Spring's web framework is a well-designed web MVC framework, which provides a great alternative to web frameworks such as Struts or other over-engineered or less popular web frameworks.
11020 | *   **Transaction Management** − Spring provides a consistent transaction management interface that can scale down to a local transaction (using a single database, for example) and scale up to global transactions (using JTA, for example).
11021 | *   **Exception Handling** − Spring provides a convenient API to translate technology-specific exceptions (thrown by JDBC, Hibernate, or JDO, for example) into consistent, unchecked exceptions.
11022 | 
11023 | **Source:** _tutorialspoint.com_
11024 | 
11025 | #### Q41: What are Spring beans? ⭐⭐
11026 | **Answer:**
11027 | The objects that form the backbone of your application and that are managed by the Spring IoC container are called **beans**. A bean is an object that is instantiated, assembled, and otherwise managed by a Spring IoC container. These beans are created with the configuration metadata that you supply to the container, for example, in the form of XML `<bean/>` definitions.
11028 | 
11029 | **Source:** _tutorialspoint.com_
11030 | 
11031 | #### Q42: What are ORM's Spring supports? ⭐⭐
11032 | **Answer:**
11033 | Spring supports the following ORM's:
11034 | 
11035 | *   Hibernate
11036 | *   iBatis
11037 | *   JPA (Java Persistence API)
11038 | *   TopLink
11039 | *   JDO (Java Data Objects)
11040 | *   OJB
11041 | 
11042 | **Source:** _tutorialspoint.com_
11043 | 
11044 | #### Q43: What is Spring Security? ⭐⭐
11045 | **Answer:**
11046 | **Spring Security** is a separate module of the Spring framework that focuses on providing authentication and authorization methods in Java applications. It also takes care of most of the common security vulnerabilities such as CSRF attacks.
11047 | 
11048 | To use Spring Security in web applications, you can get started with a simple annotation: _@EnableWebSecurity_.
11049 | 
11050 | **Source:** _developersbook.com_
11051 | 
11052 | #### Q44: Explain Bean lifecycle in Spring framework ⭐⭐⭐
11053 | **Answer:**
11054 | Following is sequence of a bean lifecycle in Spring:
11055 | 
11056 | *   **Instantiate** − First the spring container finds the bean's definition from the XML file and instantiates the bean..
11057 | *   **Populate properties** − Using the dependency injection, spring populates all of the properties as specified in the bean definition.
11058 | *   **Set Bean Name** − If the bean implements BeanNameAware interface, spring passes the bean's id to setBeanName() method.
11059 | *   **Set Bean factory** − If Bean implements BeanFactoryAware interface, spring passes the beanfactory to setBeanFactory() method.
11060 | *   **Pre Initialization** − Also called postprocess of bean. If there are any bean BeanPostProcessors associated with the bean, Spring calls postProcesserBeforeInitialization() method.
11061 | *   **Initialize beans** − If the bean implements IntializingBean,its afterPropertySet() method is called. If the bean has init method declaration, the specified initialization method is called.
11062 | *   **Post Initialization** − If there are any BeanPostProcessors associated with the bean, their postProcessAfterInitialization() methods will be called.
11063 | *   **Ready to use** − Now the bean is ready to use by the application.
11064 | *   **Destroy** − If the bean implements DisposableBean , it will call the destroy() method .
11065 | 
11066 | **Source:** _tutorialspoint.com_
11067 | 
11068 | #### Q45: What is Controller in Spring MVC framework? ⭐⭐⭐
11069 | **Answer:**
11070 | **Controllers** provide access to the application behavior that you typically define through a service interface. Controllers interpret user input and transform it into a model that is represented to the user by the view. Spring implements a controller in a very abstract way, which enables you to create a wide variety of controllers.
11071 | 
11072 | **Source:** _tutorialspoint.com_
11073 | 
11074 | #### Q46: What is Aspect? ⭐⭐⭐
11075 | **Answer:**
11076 | An **Aspect** is a module which has a set of APIs providing _cross-cutting_ requirements. For example, a logging module would be called AOP aspect for logging. An application can have any number of aspects depending on the requirement. In Spring AOP, aspects are implemented using regular classes (the schema-based approach) or regular classes annotated with the @Aspect annotation (`@AspectJ` style).
11077 | 
11078 | **Source:** _tutorialspoint.com_
11079 | 
11080 | #### Q47: What is the typical Bean life cycle in Spring Bean Factory Container? ⭐⭐⭐
11081 | **Answer:**
11082 | Bean life cycle in Spring Bean Factory Container is as follows:
11083 | 
11084 | *   The spring container finds the beans definition from the XML file and instantiates the bean.
11085 |     
11086 | *   Using the dependency injection, spring populates all of the properties as specified in the bean definition
11087 |     
11088 | *   If the bean implements the BeanNameAware interface, the factory calls `setBeanName()` passing the beans ID.
11089 |     
11090 | *   If the bean implements the BeanFactoryAware interface, the factory calls `setBeanFactory()`, passing an instance of itself.
11091 |     
11092 | *   If there are any BeanPostProcessors associated with the bean, their post- `ProcessBeforeInitialization()` methods will be called.
11093 |     
11094 | *   If an init-method is specified for the bean, it will be called.
11095 |     
11096 | *   Finally, if there are any BeanPostProcessors associated with the bean, their `postProcessAfterInitialization()` methods will be called.
11097 | 
11098 | **Source:** _developersbook.com_
11099 | 
11100 | #### Q48: How to handle exceptions in Spring MVC Framework? ⭐⭐⭐
11101 | **Answer:**
11102 |  Spring MVC Framework provides the following ways to help us achieving robust exception handling.
11103 |     
11104 | 1.  **Controller Based** – We can define exception handler methods in our controller classes. All we need is to annotate these methods with @ExceptionHandler annotation.
11105 | 2.  **Global Exception Handler** – Exception Handling is a cross-cutting concern and Spring provides @ControllerAdvice annotation that we can use with any class to define our global exception handler.
11106 | 3.  **HandlerExceptionResolver implementation** – For generic exceptions, most of the times we serve static pages. Spring Framework provides `HandlerExceptionResolver` interface that we can implement to create global exception handler. The reason behind this additional way to define global exception handler is that Spring framework also provides default implementation classes that we can define in our spring bean configuration file to get spring framework exception handling benefits.
11107 | 
11108 | **Source:** _journaldev.com_
11109 | 
11110 | #### Q49: What is Spring IoC Container? ⭐⭐⭐
11111 | **Answer:**
11112 |  **Inversion of Control** (IoC) is the mechanism to achieve loose-coupling between Objects dependencies. To achieve loose coupling and dynamic binding of the objects at runtime, the objects define their dependencies that are being injected by other assembler objects. Spring IoC container is the program that injects dependencies into an object and makes it ready for our use.
11113 |     
11114 | Spring Framework IoC container classes are part of `org.springframework.beans` and `org.springframework.context` packages and provides us different ways to decouple the object dependencies.
11115 |     
11116 | Some of the useful ApplicationContext implementations that we use are;
11117 |     
11118 | *   `AnnotationConfigApplicationContext`: For standalone java applications using annotations based configuration.
11119 | *   `ClassPathXmlApplicationContext`: For standalone java applications using XML based configuration.
11120 | *   `FileSystemXmlApplicationContext`: Similar to ClassPathXmlApplicationContext except that the xml configuration file can be loaded from anywhere in the file system.
11121 | *   `AnnotationConfigWebApplicationContext` and `XmlWebApplicationContext` for web applications.
11122 | 
11123 | **Source:** _journaldev.com_
11124 | 
11125 | #### Q50: Is the DispatcherServlet instantiated via an application context? ⭐⭐⭐
11126 | **Answer:**
11127 | No, the `DispatcherServlet` is instantiated by Servlet containers like Tomcat or Jetty. You must define the `DispatcherServlet` into the web.xml file as shown below.
11128 | 
11129 | You can see that load-on-startup tag is 1, which means `DispatcherServlet` is instantiated when you deploy the Spring MVC application to Tomcat or any other Servlet container. During instantiation, it looks for a file servlet-name-context.xml and then initializes beans defined in this file.
11130 | 
11131 | **Source:** _dzone.com_
11132 | 
11133 | #### Q51: What is the purpose of the session scope? ⭐⭐⭐
11134 | **Answer:**
11135 | The purpose of the **session scope** is to create an instance of the bean for an HTTP Session. This means the same bean can serve multiple requests if it is scoped in session. You can define the scope of a Spring bean using scope attribute or the `@Scope` annotation in a Spring MVC application.
11136 | 
11137 | **Source:** _dzone.com_
11138 | 
11139 | #### Q52: What bean scopes does Spring support? Explain them. ⭐⭐⭐⭐
11140 | **Answer:**
11141 | Read Full Answer on 👉 <a href='https://www.fullstack.cafe\blog\java-spring-interview-questions'>FullStack.Cafe</a>
11142 | 
11143 | #### Q53: What is Weaving? ⭐⭐⭐⭐
11144 | **Answer:**
11145 | Read Full Answer on 👉 <a href='https://www.fullstack.cafe\blog\java-spring-interview-questions'>FullStack.Cafe</a>
11146 | 
11147 | #### Q54: What is the difference between concern and cross-cutting concern in Spring AOP? ⭐⭐⭐⭐
11148 | **Answer:**
11149 | Read Full Answer on 👉 <a href='https://www.fullstack.cafe\blog\java-spring-interview-questions'>FullStack.Cafe</a>
11150 | 
11151 | #### Q55: What are some benefits of using Spring Transactions? ⭐⭐⭐⭐
11152 | **Answer:**
11153 | Read Full Answer on 👉 <a href='https://www.fullstack.cafe\blog\java-spring-interview-questions'>FullStack.Cafe</a>
11154 | 
11155 | #### Q56: What is Aspect-Oriented Programming? ⭐⭐⭐⭐
11156 | **Answer:**
11157 | Read Full Answer on 👉 <a href='https://www.fullstack.cafe\blog\java-spring-interview-questions'>FullStack.Cafe</a>
11158 | 
11159 | #### Q57: What is Spring WebFlux? ⭐⭐⭐⭐
11160 | **Answer:**
11161 | Read Full Answer on 👉 <a href='https://www.fullstack.cafe\blog\java-spring-interview-questions'>FullStack.Cafe</a>
11162 | 
11163 | #### Q58: Compare @Component (v2.5) versus @Bean (v 3.0) ⭐⭐⭐⭐
11164 | **Details:**
11165 | Would it have been possible to re-use the @Component annotation instead of introducing @Bean annotation? 
11166 | 
11167 | **Answer:**
11168 | Read Full Answer on 👉 <a href='https://www.fullstack.cafe\blog\java-spring-interview-questions'>FullStack.Cafe</a>
11169 | 
11170 | #### Q59: What are some of the best practices for Spring Framework? ⭐⭐⭐⭐⭐
11171 | **Answer:**
11172 | Read Full Answer on 👉 <a href='https://www.fullstack.cafe\blog\java-spring-interview-questions'>FullStack.Cafe</a>
11173 | 
11174 | #### Q60: How does autowiring work in Spring? ⭐⭐⭐⭐⭐
11175 | **Answer:**
11176 | Read Full Answer on 👉 <a href='https://www.fullstack.cafe\blog\java-spring-interview-questions'>FullStack.Cafe</a>
11177 | 
11178 | ## [[⬆]](#toc) <a name=70C#InterviewQuestionsYouMustKnow[2019Update]>70 C# Interview Questions You Must Know [2019 Update]</a>
11179 | > Originally published on 👉 <a href='https://www.fullstack.cafe\blog\c-sharp-interview-questions'>70 C# Interview Questions You Must Know [2019 Update] | FullStack.Cafe</a>
11180 | 
11181 | #### Q1: What is the .NET Framework? ⭐
11182 | **Answer:**
11183 | The .NET is a Framework, which is a collection of classes of reusable libraries given by Microsoft to be used in other .NET applications and to develop, build and deploy many types of applications on the Windows platform including the following:
11184 | 
11185 | *   Console Applications
11186 | *   Windows Forms Applications
11187 | *   Windows Presentation Foundation (WPF) Applications
11188 | *   Web Applications
11189 | *   Web Services
11190 | *   Windows Services
11191 | *   Services-oriented applications using Windows Communications Foundation (WCF)
11192 | *   Workflow-enabled applications using Windows Workflow Foundation(WF)
11193 | 
11194 | **Source:** _c-sharpcorner.com_
11195 | 
11196 | #### Q2: What is .NET Standard? ⭐
11197 | **Answer:**
11198 | The **.NET Standard** is a formal specification of .NET APIs that are intended to be available on all .NET implementations.
11199 | 
11200 | **Source:** _docs.microsoft.com_
11201 | 
11202 | #### Q3: What is a .NET application domain? ⭐⭐
11203 | **Answer:**
11204 | It is an isolation layer provided by the .NET runtime. As such, App domains live with in a process (1 process can have many app domains) and have their own virtual address space.
11205 | 
11206 | App domains are useful because:
11207 | 
11208 | * They are less expensive than full processes
11209 | * They are multithreaded
11210 | * You can stop one without killing everything in the process
11211 | * Segregation of resources/config/etc
11212 | * Each app domain runs on its own security level
11213 | 
11214 | **Source:** _stackoverflow.com_
11215 | 
11216 | #### Q4: When should we use .NET Core and .NET Standard Class Library project types? ⭐⭐⭐
11217 | **Answer:**
11218 | * Use a **.NET Standard** library when you want to increase the number of apps that will be compatible with your library, and you are okay with a decrease in the .NET API surface area your library can access.
11219 | 
11220 | * Use a **.NET Core** library when you want to increase the .NET API surface area your library can access, and you are okay with allowing only .NET Core apps to be compatible with your library.
11221 | 
11222 | **Source:** _stackoverflow.com_
11223 | 
11224 | #### Q5: How to choose the target version of .NET Standard library? ⭐⭐⭐⭐
11225 | **Answer:**
11226 | Read Full Answer on 👉 <a href='https://www.fullstack.cafe\blog\c-sharp-interview-questions'>FullStack.Cafe</a>
11227 | 
11228 | #### Q6: What is an Object? ⭐
11229 | **Answer:**
11230 | According to MSDN, "_a class or struct definition is like a blueprint that specifies what the type can do. An object is basically a block of memory that has been allocated and configured according to the blueprint. A program may create many objects of the same class. Objects are also called instances, and they can be stored in either a named variable or in an array or collection. Client code is the code that uses these variables to call the methods and access the public properties of the object. In an object-oriented language such as C#, a typical program consists of multiple objects interacting dynamically"._
11231 | 
11232 | Objects helps us to access the member of a class or struct either they can be fields, methods or properties, by using the dot. 
11233 | 
11234 | **Source:** _c-sharpcorner.com_
11235 | 
11236 | #### Q7: What is Managed or Unmanaged Code? ⭐⭐
11237 | **Answer:**
11238 | * **Managed Code**  - The code, which is developed in .NET framework is known as managed code. This code is directly executed by CLR with the help of managed code execution. Any language that is written in .NET Framework is managed code.
11239 | * **Unmanaged Code** - The code, which is developed outside .NET framework is known as unmanaged code. Applications that do not run under the control of the CLR are said to be unmanaged, and certain languages such as C++ can be used to write such applications, which, for example, access low - level functions of the operating system. Background compatibility with the code of VB, ASP and COM are examples of unmanaged code.
11240 | 
11241 | 
11242 | **Source:** _c-sharpcorner.com_
11243 | 
11244 | #### Q8: What is Boxing and Unboxing? ⭐⭐
11245 | **Answer:**
11246 | Boxing and Unboxing both are used for type conversion but have some difference:
11247 | 
11248 | * **Boxing** - Boxing is the process of converting a value type data type to the object or to any interface data type which is implemented by this value type. When the CLR boxes a value means when CLR is converting a value type to Object Type, it wraps the value inside a System.Object and stores it on the heap area in application domain.
11249 | 
11250 | * **Unboxing** - Unboxing is also a process which is used to extract the value type from the object or any implemented interface type. Boxing may be done implicitly, but unboxing have to be explicit by code. 
11251 | 
11252 | The concept of boxing and unboxing underlines the C# unified view of the type system in which a value of any type can be treated as an object.
11253 | 
11254 | **Source:** _c-sharpcorner.com_
11255 | 
11256 | #### Q9: What are generics in C#? ⭐⭐
11257 | **Answer:**
11258 | **Generics** allow you to delay the specification of the data type of programming elements in a class or a method, until it is actually used in the program. In other words, generics allow you to write a class or method that can work with any data type.
11259 | 
11260 | **Source:** _c-sharpcorner.com_
11261 | 
11262 | #### Q10: What is Serialization? ⭐⭐
11263 | **Answer:**
11264 | **Serialization** means saving the state of your object to secondary memory, such as a file.
11265 | 
11266 | 1.  Binary serialization (Save your object data into binary format).  
11267 | 2.  Soap Serialization (Save your object data into binary format; mainly used in network related communication).  
11268 | 3.  XmlSerialization (Save your object data into an XML file).
11269 | 
11270 | **Source:** _c-sharpcorner.com_
11271 | 
11272 | #### Q11: Why can't you specify the accessibility modifier for methods inside the interface? ⭐⭐
11273 | **Answer:**
11274 | In an interface, we have virtual methods that do not have method definition. All the methods are there to be overridden in the derived class. That's why they all are public.
11275 | 
11276 | **Source:** _guru99.com_
11277 | 
11278 | #### Q12: What is an Abstract Class? ⭐⭐
11279 | **Answer:**
11280 | An **Abstract class** is a class which is denoted by abstract keyword and can be used only as a Base class. An Abstract class should always be inherited. An instance of the class itself cannot be created. If we do not want any program to create an object of a class, then such classes can be made abstract.
11281 | 
11282 | Any method in the abstract class does not have implementations in the same class. But they must be implemented in the child class.
11283 | 
11284 | **Source:** _softwaretestinghelp.com_
11285 | 
11286 | #### Q13: In how many ways you can pass parameters to a method? ⭐⭐
11287 | **Answer:**
11288 | There are three ways that parameters can be passed to a method:
11289 | 
11290 | *   **Value parameters** − This method copies the actual value of an argument into the formal parameter of the function. In this case, changes made to the parameter inside the function have no effect on the argument.
11291 | *   **Reference parameters** − This method copies the reference to the memory location of an argument into the formal parameter. This means that changes made to the parameter affect the argument.
11292 | *   **Output parameters** − This method helps in returning more than one value.
11293 | 
11294 | **Source:** _tutorialspoint.com_
11295 | 
11296 | #### Q14: What are reference types in C#? ⭐⭐
11297 | **Answer:**
11298 | The **reference types** do not contain the actual data stored in a variable, but they contain a reference to the variables.
11299 | 
11300 | In other words, they refer to a memory location. Using multiple variables, the reference types can refer to a memory location. If the data in the memory location is changed by one of the variables, the other variable automatically reflects this change in value. Example of built-in reference types are: object, dynamic, and string.
11301 | 
11302 | **Source:** _tutorialspoint.com_
11303 | 
11304 | #### Q15: What are nullable types in C#? ⭐⭐
11305 | **Answer:**
11306 | C# provides a special data types, the **nullable types**, to which you can assign normal range of values as well as null values.
11307 | 
11308 | For example, you can store any value from -2,147,483,648 to 2,147,483,647 or null in a `Nullable<Int32>` variable. Similarly, you can assign true, false, or null in a `Nullable<bool>` variable.
11309 | 
11310 | **Source:** _tutorialspoint.com_
11311 | 
11312 | #### Q16: Why to use “finally” block in C#? ⭐⭐
11313 | **Answer:**
11314 | **Finally** block will be executed irrespective of exception. So while executing the code in try block when exception is occurred, control is returned to catch block and at last `finally` block will be executed. So closing connection to database / releasing the file handlers can be kept in `finally` block.
11315 | 
11316 | **Source:** _a4academics.com_
11317 | 
11318 | #### Q17: What is the difference between Interface and Abstract Class? ⭐⭐⭐
11319 | **Answer:**
11320 | There are some differences between **Abstract Class** and **Interface** which are listed below:
11321 | 
11322 | * A class can implement any number of interfaces but a subclass can at most use only one abstract class.  
11323 | * An abstract class can have non-abstract methods (concrete methods) while in case of interface all the methods has to be abstract.  
11324 | * An abstract class can declare or use any variables while an interface is not allowed to do so.
11325 | * In an abstract class all data member or functions are private by default while in interface all are public, we can't change them manually.  
11326 | * In an abstract class we need to use abstract keyword to declare abstract methods while in an interface we don't need to use that.  
11327 | * An abstract class can't be used for multiple inheritance while interface can be used as multiple inheritance.  
11328 | * An abstract class use constructor while in an interface we don't have any type of constructor.
11329 | 
11330 | **Source:** _c-sharpcorner.com_
11331 | 
11332 | #### Q18: What is the difference between overloading and overriding? ⭐⭐⭐
11333 | **Answer:**
11334 | * **Overloading** is when you have multiple methods in the same scope, with the same name but different signatures.
11335 | 
11336 | ```csharp
11337 | //Overloading
11338 | public class test
11339 | {
11340 |     public void getStuff(int id)
11341 |     {}
11342 |     public void getStuff(string name)
11343 |     {}
11344 | }
11345 | ```
11346 | * **Overriding** is a principle that allows you to change the functionality of a method in a child class.
11347 | 
11348 | ```csharp
11349 | //Overriding
11350 | public class test
11351 | {
11352 |         public virtual void getStuff(int id)
11353 |         {
11354 |             //Get stuff default location
11355 |         }
11356 | }
11357 | 
11358 | public class test2 : test
11359 | {
11360 |         public override void getStuff(int id)
11361 |         {
11362 |             //base.getStuff(id);
11363 |             //or - Get stuff new location
11364 |         }
11365 | }
11366 | ```
11367 | 
11368 | **Source:** _stackoverflow.com_
11369 | 
11370 | #### Q19: What is Virtual Method in C#? ⭐⭐⭐
11371 | **Answer:**
11372 | A virtual method is a method that can be redefined in derived classes. A virtual method has an implementation in a base class as well as derived class. When a virtual method is invoked, the run-time type of the object is checked for an overriding member. 
11373 | 
11374 | 1.  By default, methods are non-virtual. We can't override a non-virtual method.  
11375 | 2.  We can't use the virtual modifier with the static, abstract, private or override modifiers.
11376 | 
11377 | **Source:** _c-sharpcorner.com_
11378 | 
11379 | #### Q20: Explain Anonymous type in C# ⭐⭐⭐
11380 | **Answer:**
11381 | **Anonymous types** allow us to create a new type without defining them. This is way to defining read only properties into a single object without having to define type explicitly. Here Type is generating by the compiler and it is accessible only for the current block of code. The type of properties is also inferred by the compiler.  
11382 | 
11383 | Consider:
11384 | ```csharp
11385 | var anonymousData = new
11386 | {  
11387 |      ForeName = "Jignesh",  
11388 |      SurName = "Trivedi"
11389 | };  
11390 | 
11391 | Console.WriteLine("First Name : " + anonymousData.ForeName); 
11392 | ```
11393 | 
11394 | **Source:** _c-sharpcorner.com_
11395 | 
11396 | #### Q21: What is difference between constants and readonly? ⭐⭐⭐
11397 | **Answer:**
11398 | Constant variables are declared and initialized at compile time. The value can't be changed afterwards. Readonly is used only when we want to assign the value at run time.
11399 | 
11400 | **Source:** _guru99.com_
11401 | 
11402 | #### Q22: What is the difference between Virtual method and Abstract method? ⭐⭐⭐
11403 | **Answer:**
11404 | * A **Virtual method** must always have a default implementation. However, it can be overridden in the derived class, though not mandatory. It can be overridden using _override_ keyword.
11405 | * An **Abstract method** does not have an implementation. It resides in the abstract class. It is mandatory that the derived class implements the abstract method. An _override_ keyword is not necessary here though it can be used.
11406 | 
11407 | **Source:** _softwaretestinghelp.com_
11408 | 
11409 | #### Q23: What is the difference between dynamic type variables and object type variables? ⭐⭐⭐
11410 | **Answer:**
11411 | Dynamic types are similar to object types except that type checking for object type variables takes place at compile time, whereas that for the dynamic type variables takes place at run time.
11412 | 
11413 | **Source:** _tutorialspoint.com_
11414 | 
11415 | #### Q24: What is the use of Null Coalescing Operator (??) in C#? ⭐⭐⭐
11416 | **Answer:**
11417 | The **??** operator is called the **null-coalescing operator** and is used to define a default value for nullable value types or reference types. It returns the left-hand operand if the operand is not null; otherwise, it returns the right operand. 
11418 | 
11419 | ```csharp
11420 | string name = null;  
11421 | string myname = name ?? "Laxmi";  
11422 | Console.WriteLine(myname);  
11423 | ```
11424 | 
11425 | **Source:** _tutorialspoint.com_
11426 | 
11427 | #### Q25: What is the output of the program below? Explain your answer. ⭐⭐⭐
11428 | **Details:**
11429 | Consider:
11430 | ```csharp
11431 | delegate void Printer();
11432 | 
11433 | static void Main()
11434 | {
11435 |         List<Printer> printers = new List<Printer>();
11436 |         int i=0;
11437 |         for(; i < 10; i++)
11438 |         {
11439 |             printers.Add(delegate { Console.WriteLine(i); });
11440 |         }
11441 | 
11442 |         foreach (var printer in printers)
11443 |         {
11444 |             printer();
11445 |         }
11446 | }
11447 | ```
11448 | 
11449 | **Answer:**
11450 | This program will output the number 10 ten times.
11451 | 
11452 | Here’s why: The delegate is added in the for loop and “reference” (or perhaps “pointer” would be a better choice of words) to `i` is stored, rather than the value itself. Therefore, after we exit the loop, the variable `i` has been set to 10, so by the time each delegate is invoked, the value passed to all of them is 10.
11453 | 
11454 | **Source:** _toptal.com_
11455 | 
11456 | #### Q26: What is marshalling and why do we need it? ⭐⭐⭐⭐
11457 | **Answer:**
11458 | Read Full Answer on 👉 <a href='https://www.fullstack.cafe\blog\c-sharp-interview-questions'>FullStack.Cafe</a>
11459 | 
11460 | #### Q27: What is the Constructor Chaining in C#? ⭐⭐⭐⭐
11461 | **Answer:**
11462 | Read Full Answer on 👉 <a href='https://www.fullstack.cafe\blog\c-sharp-interview-questions'>FullStack.Cafe</a>
11463 | 
11464 | #### Q28: What is an Object Pool in .Net? ⭐⭐⭐⭐
11465 | **Answer:**
11466 | Read Full Answer on 👉 <a href='https://www.fullstack.cafe\blog\c-sharp-interview-questions'>FullStack.Cafe</a>
11467 | 
11468 | #### Q29: What are the differences between a multidimensional array and an array of arrays in C#? ⭐⭐⭐⭐
11469 | **Details:**
11470 | What are the differences between multidimensional arrays `double[,]` and array-of-arrays `double[][]` in C#?
11471 | 
11472 | **Answer:**
11473 | Read Full Answer on 👉 <a href='https://www.fullstack.cafe\blog\c-sharp-interview-questions'>FullStack.Cafe</a>
11474 | 
11475 | #### Q30: What are the different ways a method can be overloaded? ⭐⭐⭐⭐
11476 | **Answer:**
11477 | Read Full Answer on 👉 <a href='https://www.fullstack.cafe\blog\c-sharp-interview-questions'>FullStack.Cafe</a>
11478 | 
11479 | #### Q31: Can you create a function in C# which can accept varying number of arguments? ⭐⭐⭐⭐
11480 | **Answer:**
11481 | Read Full Answer on 👉 <a href='https://www.fullstack.cafe\blog\c-sharp-interview-questions'>FullStack.Cafe</a>
11482 | 
11483 | #### Q32: Is operator overloading supported in C#? ⭐⭐⭐⭐
11484 | **Answer:**
11485 | Read Full Answer on 👉 <a href='https://www.fullstack.cafe\blog\c-sharp-interview-questions'>FullStack.Cafe</a>
11486 | 
11487 | #### Q33: What is the use of conditional preprocessor directive in C#? ⭐⭐⭐⭐
11488 | **Answer:**
11489 | Read Full Answer on 👉 <a href='https://www.fullstack.cafe\blog\c-sharp-interview-questions'>FullStack.Cafe</a>
11490 | 
11491 | #### Q34: Can we have only “try” block without “catch” block in C#? ⭐⭐⭐⭐
11492 | **Answer:**
11493 | Read Full Answer on 👉 <a href='https://www.fullstack.cafe\blog\c-sharp-interview-questions'>FullStack.Cafe</a>
11494 | 
11495 | #### Q35: What are the uses of delegates in C#? ⭐⭐⭐⭐
11496 | **Answer:**
11497 | Read Full Answer on 👉 <a href='https://www.fullstack.cafe\blog\c-sharp-interview-questions'>FullStack.Cafe</a>
11498 | 
11499 | #### Q36: Can Multiple Inheritance implemented in C# ? ⭐⭐⭐⭐
11500 | **Answer:**
11501 | Read Full Answer on 👉 <a href='https://www.fullstack.cafe\blog\c-sharp-interview-questions'>FullStack.Cafe</a>
11502 | 
11503 | #### Q37: What is the output of the program below? Explain your answer. ⭐⭐⭐⭐
11504 | **Details:**
11505 | Consider:
11506 | ```csharp
11507 | class Program {
11508 |   private static string result;
11509 |  
11510 |   static void Main() {
11511 |     SaySomething();
11512 |     Console.WriteLine(result);
11513 |   }
11514 |  
11515 |   static async Task<string> SaySomething() {
11516 |     await Task.Delay(5);
11517 |     result = "Hello world!";
11518 |     return “Something”;
11519 |   }
11520 | }
11521 | ```
11522 | Also, would the answer change if we were to replace `await Task.Delay(5);` with `Thread.Sleep(5)`? Why or why not?
11523 | 
11524 | **Answer:**
11525 | Read Full Answer on 👉 <a href='https://www.fullstack.cafe\blog\c-sharp-interview-questions'>FullStack.Cafe</a>
11526 | 
11527 | #### Q38: What is the "yield" keyword used for in C#? ⭐⭐⭐⭐
11528 | **Details:**
11529 | Consider:
11530 | ```csharp
11531 | IEnumerable<object> FilteredList()
11532 | {
11533 |     foreach( object item in FullList )
11534 |     {
11535 |         if( IsItemInPartialList( item )
11536 |             yield return item;
11537 |     }
11538 | }
11539 | ```
11540 | Could you explain what does the `yield` keyword do there?
11541 | 
11542 | **Answer:**
11543 | Read Full Answer on 👉 <a href='https://www.fullstack.cafe\blog\c-sharp-interview-questions'>FullStack.Cafe</a>
11544 | 
11545 | #### Q39: Explain what is short-circuit evaluation in C# ⭐⭐⭐⭐
11546 | **Answer:**
11547 | Read Full Answer on 👉 <a href='https://www.fullstack.cafe\blog\c-sharp-interview-questions'>FullStack.Cafe</a>
11548 | 
11549 | #### Q40: What is deep or shallow copy concept in C#? ⭐⭐⭐⭐⭐
11550 | **Answer:**
11551 | Read Full Answer on 👉 <a href='https://www.fullstack.cafe\blog\c-sharp-interview-questions'>FullStack.Cafe</a>
11552 | 
11553 | #### Q41: What is multicast delegate in C#? ⭐⭐⭐⭐⭐
11554 | **Answer:**
11555 | Read Full Answer on 👉 <a href='https://www.fullstack.cafe\blog\c-sharp-interview-questions'>FullStack.Cafe</a>
11556 | 
11557 | #### Q42: List some different ways for equality check in .Net ⭐⭐⭐⭐⭐
11558 | **Answer:**
11559 | Read Full Answer on 👉 <a href='https://www.fullstack.cafe\blog\c-sharp-interview-questions'>FullStack.Cafe</a>
11560 | 
11561 | #### Q43: What is a preprocessor directives in C#? ⭐⭐⭐⭐⭐
11562 | **Answer:**
11563 | Read Full Answer on 👉 <a href='https://www.fullstack.cafe\blog\c-sharp-interview-questions'>FullStack.Cafe</a>
11564 | 
11565 | #### Q44: Calculate the circumference of the circle ⭐⭐⭐⭐⭐
11566 | **Details:**
11567 | Given an instance circle of the following class:
11568 | 
11569 | ```csharp
11570 | public sealed class Circle {
11571 |   private double radius;
11572 |   
11573 |   public double Calculate(Func<double, double> op) {
11574 |     return op(radius);
11575 |   }
11576 | }
11577 | 
11578 | write code to calculate the circumference of the circle, without modifying the `Circle` class itself.
11579 | ```
11580 | 
11581 | **Answer:**
11582 | Read Full Answer on 👉 <a href='https://www.fullstack.cafe\blog\c-sharp-interview-questions'>FullStack.Cafe</a>
11583 | 
11584 | #### Q45: What is the difference between lambdas and delegates? ⭐⭐⭐⭐⭐
11585 | **Answer:**
11586 | Read Full Answer on 👉 <a href='https://www.fullstack.cafe\blog\c-sharp-interview-questions'>FullStack.Cafe</a>
11587 | 
11588 | #### Q46: Could you explain the difference between Func vs. Action vs. Predicate? ⭐⭐⭐⭐⭐
11589 | **Answer:**
11590 | Read Full Answer on 👉 <a href='https://www.fullstack.cafe\blog\c-sharp-interview-questions'>FullStack.Cafe</a>
11591 | 
11592 | #### Q47: Can you add extension methods to an existing static class? ⭐⭐⭐⭐⭐
11593 | **Answer:**
11594 | Read Full Answer on 👉 <a href='https://www.fullstack.cafe\blog\c-sharp-interview-questions'>FullStack.Cafe</a>
11595 | 
11596 | #### Q48: Implement the "Where" method in C# ⭐⭐⭐⭐⭐
11597 | **Answer:**
11598 | Read Full Answer on 👉 <a href='https://www.fullstack.cafe\blog\c-sharp-interview-questions'>FullStack.Cafe</a>
11599 | 
11600 | #### Q49: Explain what is weak reference in C#? ⭐⭐⭐⭐⭐
11601 | **Answer:**
11602 | Read Full Answer on 👉 <a href='https://www.fullstack.cafe\blog\c-sharp-interview-questions'>FullStack.Cafe</a>
11603 | 
11604 | #### Q50: What is Anonymous function? ⭐⭐
11605 | **Answer:**
11606 | An Anonymous function is a special function which does not have any name. We just define their parameters and define the code into the curly braces.
11607 | 
11608 | Consider:
11609 | ```csharp
11610 | delegate int func(int a, int b);
11611 | static void Main(string[] args)
11612 | {
11613 |     func f1 = delegate(int a, int b)
11614 |     {
11615 |         return a + b;
11616 |     };
11617 |  
11618 |     Console.WriteLine(f1(1, 2));
11619 | }
11620 | ```
11621 | 
11622 | **Source:** _stackoverflow.com_
11623 | 
11624 | #### Q51: Mention what is the role of DataContext classes in LINQ? ⭐⭐
11625 | **Answer:**
11626 | **DataContext** class acts as a bridge between SQL Server database and the LINQ to SQL. For accessing the database and also for changing the data in the database, it contains connections string and the functions. Essentially a DataContext class performs the following three tasks:
11627 | 
11628 | * Create connection to database.
11629 | * It submits and retrieves object to database.
11630 | * Converts objects to SQL queries and vice versa.
11631 | 
11632 | **Source:** _career.guru99.com_
11633 | 
11634 | #### Q52: Using LINQ to remove elements from a List<T> ⭐⭐⭐
11635 | **Details:**
11636 | Given that `authorsList` is of type `List<Author>`, how can I delete the `Author` elements that are equalling to `Bob`?
11637 | 
11638 | **Answer:**
11639 | Consider:
11640 | ```csharp
11641 | authorsList.RemoveAll(x => x.FirstName == "Bob");
11642 | ```
11643 | 
11644 | **Source:** _stackoverflow.com_
11645 | 
11646 | #### Q53: What is Expression Trees and how they used in LINQ? ⭐⭐⭐
11647 | **Answer:**
11648 | An **Expression Tree** is a data structure that contains Expressions, which is basically code. So it is a tree structure that represents a calculation you may make in code. These pieces of code can then be executed by "running" the expression tree over a set of data.
11649 | 
11650 | In LINQ, expression trees are used to represent structured queries that target sources of data that implement `IQueryable<T>`. For example, the LINQ provider implements the `IQueryable<T>` interface for querying relational data stores. The C# compiler compiles queries that target such data sources into code that builds an expression tree at runtime. The query provider can then traverse the expression tree data structure and translate it into a query language appropriate for the data source.
11651 | 
11652 | **Source:** _docs.microsoft.com_
11653 | 
11654 | #### Q54: Get the indexes of top n items where item value = true ⭐⭐⭐
11655 | **Details:**
11656 | I have a `List<bool>`. I need to get the indexes of top n items where item `value = true`.
11657 | 
11658 | ```csharp
11659 | 10011001000
11660 | 
11661 | TopTrueIndexes(3) = The first 3 indexes where bits are true are 0, 3, 4 
11662 | TopTrueIndexes(4) = The first 4 indexes where bits are true are 0, 3, 4, 7 
11663 | ```
11664 | 
11665 | 
11666 | **Answer:**
11667 | Assuming you have some easily-identifiable condition, you can do something like this, which will work for any `IEnumerable<T>`:
11668 | ```csharp
11669 | var query = source.Select((value, index) => new { value, index })
11670 |                   .Where(x => x.value => Condition(value))
11671 |                   .Select(x => x.index)
11672 |                   .Take(n);
11673 | ```
11674 | The important bits are that you use the overload of `Select` to get index/value pairs before the Where, and then another Select to get just the indexes after the Where... and use Take to only get the first n results.
11675 | 
11676 | **Source:** _stackoverflow.com_
11677 | 
11678 | #### Q55: Name some advantages of LINQ over Stored Procedures ⭐⭐⭐⭐
11679 | **Answer:**
11680 | Read Full Answer on 👉 <a href='https://www.fullstack.cafe\blog\c-sharp-interview-questions'>FullStack.Cafe</a>
11681 | 
11682 | #### Q56: When should I use a CompiledQuery? ⭐⭐⭐⭐
11683 | **Answer:**
11684 | Read Full Answer on 👉 <a href='https://www.fullstack.cafe\blog\c-sharp-interview-questions'>FullStack.Cafe</a>
11685 | 
11686 | #### Q57: Name some disadvantages of LINQ over sprocs ⭐⭐⭐⭐⭐
11687 | **Answer:**
11688 | Read Full Answer on 👉 <a href='https://www.fullstack.cafe\blog\c-sharp-interview-questions'>FullStack.Cafe</a>
11689 | 
11690 | #### Q58: A structure in C# can implement one or more interfaces. Is it true or false? ⭐⭐⭐
11691 | **Answer:**
11692 | Yes, it is true. Like classes, in C#, structures can implement one or more interfaces.
11693 | 
11694 | **Source:** _indiabix.com_
11695 | 
11696 | #### Q59: Can you allow a class to be inherited, but prevent a method from being overridden in C#? ⭐⭐⭐
11697 | **Answer:**
11698 | Yes. Just declare the class `public` and make the method `sealed`.
11699 | 
11700 | **Source:** _indiabix.com_
11701 | 
11702 | #### Q60: How can you prevent a class from overriding in C#? ⭐⭐⭐
11703 | **Answer:**
11704 | You can prevent a class from overriding in C# by using the `sealed` keyword.
11705 | 
11706 | **Source:** _indiabix.com_
11707 | 
11708 | #### Q61: Can you specify the accessibility modifier for methods inside the interface? ⭐⭐⭐
11709 | **Answer:**
11710 | All the methods inside an interface are always `public`, by default. You cannot specify any other access modifier for them.
11711 | 
11712 | **Source:** _indiabix.com_
11713 | 
11714 | #### Q62: What is Coupling in OOP? ⭐⭐⭐⭐
11715 | **Answer:**
11716 | Read Full Answer on 👉 <a href='https://www.fullstack.cafe\blog\c-sharp-interview-questions'>FullStack.Cafe</a>
11717 | 
11718 | #### Q63: What is Cohesion in OOP? ⭐⭐⭐⭐
11719 | **Answer:**
11720 | Read Full Answer on 👉 <a href='https://www.fullstack.cafe\blog\c-sharp-interview-questions'>FullStack.Cafe</a>
11721 | 
11722 | #### Q64: Explain the concept of destructor? ⭐⭐⭐⭐
11723 | **Answer:**
11724 | Read Full Answer on 👉 <a href='https://www.fullstack.cafe\blog\c-sharp-interview-questions'>FullStack.Cafe</a>
11725 | 
11726 | #### Q65: Explain different types of inheritance. ⭐⭐⭐⭐
11727 | **Answer:**
11728 | Read Full Answer on 👉 <a href='https://www.fullstack.cafe\blog\c-sharp-interview-questions'>FullStack.Cafe</a>
11729 | 
11730 | #### Q66: Why Doesn't C# Allow Static Methods to Implement an Interface? ⭐⭐⭐⭐⭐
11731 | **Answer:**
11732 | Read Full Answer on 👉 <a href='https://www.fullstack.cafe\blog\c-sharp-interview-questions'>FullStack.Cafe</a>
11733 | 
11734 | #### Q67: What is LSP (Liskov Substitution Principle) and what are some examples of its use (good and bad)? ⭐⭐⭐⭐⭐
11735 | **Answer:**
11736 | Read Full Answer on 👉 <a href='https://www.fullstack.cafe\blog\c-sharp-interview-questions'>FullStack.Cafe</a>
11737 | 
11738 | #### Q68: Why prefer composition over inheritance? What trade-offs are there for each approach? When should you choose inheritance over composition? ⭐⭐⭐⭐⭐
11739 | **Answer:**
11740 | Read Full Answer on 👉 <a href='https://www.fullstack.cafe\blog\c-sharp-interview-questions'>FullStack.Cafe</a>
11741 | 
11742 | #### Q69: Can you declare a private class in a namespace? ⭐⭐⭐⭐⭐
11743 | **Answer:**
11744 | Read Full Answer on 👉 <a href='https://www.fullstack.cafe\blog\c-sharp-interview-questions'>FullStack.Cafe</a>
11745 | 
11746 | #### Q70: You have defined a destructor in a class that you have developed by using the C# programming language, but the destructor never executed. Why did the destructor not execute? ⭐⭐⭐⭐⭐
11747 | **Answer:**
11748 | Read Full Answer on 👉 <a href='https://www.fullstack.cafe\blog\c-sharp-interview-questions'>FullStack.Cafe</a>
11749 | 
11750 | ## [[⬆]](#toc) <a name=75+JavaScriptInterviewQuestions[ES6/ES2015Update]in2019>75+ JavaScript Interview Questions [ES6/ES2015 Update] in 2019</a>
11751 | > Originally published on 👉 <a href='https://www.fullstack.cafe\blog\javascript-interview-questions-and-answers'>75+ JavaScript Interview Questions [ES6/ES2015 Update] in 2019 | FullStack.Cafe</a>
11752 | 
11753 | #### Q1: What is Coercion in JavaScript? 
11754 | **Answer:**
11755 | In JavaScript conversion between different two build-in types called `coercion`.  Coercion comes in two forms in JavaScript: *explicit* and *implicit*.
11756 | 
11757 | Here's an example of explicit coercion:
11758 | ```js
11759 | var a = "42";
11760 | 
11761 | var b = Number( a );
11762 | 
11763 | a;				// "42"
11764 | b;				// 42 -- the number!
11765 | ```
11766 | And here's an example of implicit coercion:
11767 | ```js
11768 | var a = "42";
11769 | 
11770 | var b = a * 1;	// "42" implicitly coerced to 42 here
11771 | 
11772 | a;				// "42"
11773 | b;				// 42 -- the number!
11774 | ``` 
11775 | 
11776 | #### Q2: What is Scope in JavaScript? ⭐
11777 | **Answer:**
11778 | In JavaScript, each function gets its own *scope*. Scope is basically a collection of variables as well as the rules for how those variables are accessed by name. Only code inside that function can access that function's scoped variables.
11779 | 
11780 | A variable name has to be unique within the same scope. A scope can be nested inside another scope. If one scope is nested inside another, code inside the innermost scope can access variables from either scope.
11781 | 
11782 | #### Q3: Explain equality in JavaScript ⭐
11783 | **Answer:**
11784 | JavaScript has both strict and type–converting comparisons: 
11785 | * **Strict comparison (e.g., ===)** checks for value equality without allowing *coercion*
11786 | * **Abstract comparison (e.g. ==)** checks for value equality with *coercion* allowed
11787 | 
11788 | ```js
11789 | var a = "42";
11790 | var b = 42;
11791 | 
11792 | a == b;			// true
11793 | a === b;		// false
11794 | ```
11795 | Some simple equalityrules:
11796 | * If either value (aka side) in a comparison could be the `true` or `false` value, avoid `==` and use `===`.
11797 | * If either value in a comparison could be of these specific values (`0`, `""`, or `[]` -- empty array), avoid `==` and use `===`.
11798 | * In all other cases, you're safe to use `==`. Not only is it safe, but in many cases it simplifies your code in a way that improves readability.
11799 | 
11800 | #### Q4: What is typeof operator? ⭐
11801 | **Answer:**
11802 | JavaScript provides a `typeof` operator that can examine a value and tell you what type it is:
11803 | ```js
11804 | var a;
11805 | typeof a;				// "undefined"
11806 | 
11807 | a = "hello world";
11808 | typeof a;				// "string"
11809 | 
11810 | a = 42;
11811 | typeof a;				// "number"
11812 | 
11813 | a = true;
11814 | typeof a;				// "boolean"
11815 | 
11816 | a = null;
11817 | typeof a;				// "object" -- weird, bug
11818 | 
11819 | a = undefined;
11820 | typeof a;				// "undefined"
11821 | 
11822 | a = { b: "c" };
11823 | typeof a;				// "object"
11824 | ```
11825 | 
11826 | 
11827 | #### Q5: What is the object type? ⭐
11828 | **Answer:**
11829 | The object type refers to a compound value where you can set properties (named locations) that each hold their own values of any type. 
11830 | 
11831 | ```js
11832 | var obj = {
11833 | 	a: "hello world", // property
11834 | 	b: 42,
11835 | 	c: true
11836 | };
11837 | 
11838 | obj.a;		// "hello world", accessed with doted notation
11839 | obj.b;		// 42
11840 | obj.c;		// true
11841 | 
11842 | obj["a"];	// "hello world", accessed with bracket notation
11843 | obj["b"];	// 42
11844 | obj["c"];	// true
11845 | ```
11846 | Bracket notation is also useful if you want to access a property/key but the name is stored in another variable, such as:
11847 | ```js
11848 | var obj = {
11849 | 	a: "hello world",
11850 | 	b: 42
11851 | };
11852 | 
11853 | var b = "a";
11854 | 
11855 | obj[b];			// "hello world"
11856 | obj["b"];		// 42
11857 | ```
11858 | 
11859 | #### Q6: Explain arrays in JavaScript ⭐
11860 | **Answer:**
11861 | An `array` is an object that holds values (of any type) not particularly in named properties/keys, but rather in numerically indexed positions:
11862 | 
11863 | ```js
11864 | var arr = [
11865 | 	"hello world",
11866 | 	42,
11867 | 	true
11868 | ];
11869 | 
11870 | arr[0];			// "hello world"
11871 | arr[1];			// 42
11872 | arr[2];			// true
11873 | arr.length;		// 3
11874 | 
11875 | typeof arr;		// "object"
11876 | ```
11877 | 
11878 | 
11879 | #### Q7: Explain Values and Types in JavaScript ⭐⭐
11880 | **Answer:**
11881 | JavaScript has typed values, not typed variables. The following built-in types are available:
11882 | * `string`
11883 | * `number`
11884 | * `boolean`
11885 | * `null` and `undefined`
11886 | * `object`
11887 | * `symbol` (new to ES6)
11888 | 
11889 | #### Q8: Explain Null and Undefined in JavaScript ⭐⭐
11890 | **Answer:**
11891 | JavaScript (and by extension TypeScript) has two bottom types: `null` and `undefined`. They are *intended* to mean different things:
11892 | * Something hasn't been initialized : `undefined`.
11893 | * Something is currently unavailable: `null`.
11894 | 
11895 | #### Q9: What is a Polyfill? ⭐⭐
11896 | **Answer:**
11897 | A polyfill is essentially the specific code (or plugin) that would allow you to have some specific functionality that you expect in current or “modern” browsers to also work in other browsers that do not have the support for that functionality built in.
11898 | * Polyfills are not part of the HTML5 standard
11899 | * Polyfilling is not limited to Javascript
11900 | 
11901 | **Source:** _programmerinterview.com_
11902 | 
11903 | #### Q10: What is let keyword in JavaScript? ⭐⭐
11904 | **Answer:**
11905 | In addition to creating declarations for variables at the function level, ES6 lets you declare variables to belong to individual blocks (pairs of { .. }), using the `let` keyword. 
11906 | 
11907 | **Source:** _github.com/getify_
11908 | 
11909 | #### Q11: Being told that an unsorted array contains (n - 1) of n consecutive numbers (where the bounds are defined), find the missing number in O(n) time ⭐⭐
11910 | **Answer:**
11911 | ```js
11912 | // The output of the function should be 8
11913 | var arrayOfIntegers = [2, 5, 1, 4, 9, 6, 3, 7];
11914 | var upperBound = 9;
11915 | var lowerBound = 1;
11916 | 
11917 | findMissingNumber(arrayOfIntegers, upperBound, lowerBound); // 8
11918 | 
11919 | function findMissingNumber(arrayOfIntegers, upperBound, lowerBound) {
11920 |   // Iterate through array to find the sum of the numbers
11921 |   var sumOfIntegers = 0;
11922 |   for (var i = 0; i < arrayOfIntegers.length; i++) {
11923 |     sumOfIntegers += arrayOfIntegers[i];
11924 |   }
11925 | 
11926 |   // Find theoretical sum of the consecutive numbers using a variation of Gauss Sum.
11927 |   // Formula: [(N * (N + 1)) / 2] - [(M * (M - 1)) / 2];
11928 |   // N is the upper bound and M is the lower bound
11929 | 
11930 |   upperLimitSum = (upperBound * (upperBound + 1)) / 2;
11931 |   lowerLimitSum = (lowerBound * (lowerBound - 1)) / 2;
11932 | 
11933 |   theoreticalSum = upperLimitSum - lowerLimitSum;
11934 | 
11935 |   return theoreticalSum - sumOfIntegers;
11936 | }
11937 | ```
11938 | 
11939 | **Source:** _https://github.com/kennymkchan_
11940 | 
11941 | #### Q12: Remove duplicates of an array and return an array of only unique elements ⭐⭐
11942 | **Answer:**
11943 | ```js
11944 | // ES6 Implementation
11945 | var array = [1, 2, 3, 5, 1, 5, 9, 1, 2, 8];
11946 | 
11947 | Array.from(new Set(array)); // [1, 2, 3, 5, 9, 8]
11948 | 
11949 | // ES5 Implementation
11950 | var array = [1, 2, 3, 5, 1, 5, 9, 1, 2, 8];
11951 | 
11952 | uniqueArray(array); // [1, 2, 3, 5, 9, 8]
11953 | 
11954 | function uniqueArray(array) {
11955 |   var hashmap = {};
11956 |   var unique = [];
11957 | 
11958 |   for(var i = 0; i < array.length; i++) {
11959 |     // If key returns undefined (unique), it is evaluated as false.
11960 |     if(!hashmap.hasOwnProperty(array[i])) {
11961 |       hashmap[array[i]] = 1;
11962 |       unique.push(array[i]);
11963 |     }
11964 |   }
11965 | 
11966 |   return unique;
11967 | }
11968 | ```
11969 | 
11970 | **Source:** _https://github.com/kennymkchan_
11971 | 
11972 | #### Q13: Given a string, reverse each word in the sentence ⭐⭐
11973 | **Details:**
11974 | For example `Welcome to this Javascript Guide!` should be become `emocleW ot siht tpircsavaJ !ediuG`
11975 | 
11976 | **Answer:**
11977 | ```js
11978 | var string = "Welcome to this Javascript Guide!";
11979 | 
11980 | // Output becomes !ediuG tpircsavaJ siht ot emocleW
11981 | var reverseEntireSentence = reverseBySeparator(string, "");
11982 | 
11983 | // Output becomes emocleW ot siht tpircsavaJ !ediuG
11984 | var reverseEachWord = reverseBySeparator(reverseEntireSentence, " ");
11985 | 
11986 | function reverseBySeparator(string, separator) {
11987 |   return string.split(separator).reverse().join(separator);
11988 | }
11989 | ```
11990 | 
11991 | **Source:** _https://github.com/kennymkchan_
11992 | 
11993 | #### Q14: Implement enqueue and dequeue using only two stacks ⭐⭐
11994 | **Answer:**
11995 | *Enqueue* means to add an element, *dequeue* to remove an element.
11996 | 
11997 | ```js
11998 | var inputStack = []; // First stack
11999 | var outputStack = []; // Second stack
12000 | 
12001 | // For enqueue, just push the item into the first stack
12002 | function enqueue(stackInput, item) {
12003 |   return stackInput.push(item);
12004 | }
12005 | 
12006 | function dequeue(stackInput, stackOutput) {
12007 |   // Reverse the stack such that the first element of the output stack is the
12008 |   // last element of the input stack. After that, pop the top of the output to
12009 |   // get the first element that was ever pushed into the input stack
12010 |   if (stackOutput.length <= 0) {
12011 |     while(stackInput.length > 0) {
12012 |       var elementToOutput = stackInput.pop();
12013 |       stackOutput.push(elementToOutput);
12014 |     }
12015 |   }
12016 | 
12017 |   return stackOutput.pop();
12018 | }
12019 | ```
12020 | 
12021 | **Source:** _https://github.com/kennymkchan_
12022 | 
12023 | #### Q15: Explain event bubbling and how one may prevent it ⭐⭐
12024 | **Answer:**
12025 | **Event bubbling** is the concept in which an event triggers at the deepest possible element, and triggers on parent elements in nesting order. As a result, when clicking on a child element one may exhibit the handler of the parent activating.
12026 | 
12027 | One way to prevent event bubbling is using `event.stopPropagation()` or `event.cancelBubble` on IE < 9.
12028 | 
12029 | **Source:** _https://github.com/kennymkchan_
12030 | 
12031 | #### Q16: How to check if an object is an array or not? Provide some code. ⭐⭐
12032 | **Answer:**
12033 | > The best way to find whether an object is instance of a particular class or not using `toString` method from `Object.prototype`
12034 | 
12035 | ```javascript
12036 | var arrayList = [1 , 2, 3];
12037 | ```
12038 | 
12039 | One of the best use cases of type checking of an object is when we do method overloading in JavaScript. For understanding this let say we have a method called `greet` which take one single string and also a list of string, so making our `greet` method workable in both situation we need to know what kind of parameter is being passed, is it single value or list of value?
12040 | 
12041 | ```javascript
12042 | function greet(param) {
12043 |   if() {
12044 |     // here have to check whether param is array or not
12045 |   }
12046 |   else {
12047 |   }
12048 | }
12049 | ```
12050 | 
12051 | However, in above implementation it might not necessary to check type for array, we can check for single value string and put array logic code in else block, let see below code for the same.
12052 | 
12053 | ```javascript
12054 |  function greet(param) {
12055 |    if(typeof param === 'string') {
12056 |    }
12057 |    else {
12058 |      // If param is of type array then this block of code would execute
12059 |    }
12060 |  }
12061 | ```
12062 | 
12063 | Now it's fine we can go with above two implementations, but when we have a situation like a parameter can be `single value`, `array`, and `object` type then we will be in trouble.
12064 | 
12065 | Coming back to checking type of object, As we mentioned that we can use `Object.prototype.toString`
12066 | 
12067 | ```javascript
12068 | if(Object.prototype.toString.call(arrayList) === '[object Array]') {
12069 |   console.log('Array!');
12070 | }
12071 | ```
12072 | 
12073 | If you are using `jQuery` then you can also used jQuery `isArray` method:
12074 | 
12075 | ```javascript
12076 | if($.isArray(arrayList)) {
12077 |   console.log('Array');
12078 | } else {
12079 |   console.log('Not an array');
12080 | }
12081 | ```
12082 | 
12083 | FYI jQuery uses `Object.prototype.toString.call` internally to check whether an object is an array or not.
12084 | 
12085 | In modern browser, you can also use:
12086 | 
12087 | ```javascript
12088 | Array.isArray(arrayList);
12089 | ```
12090 | 
12091 | `Array.isArray` is supported by Chrome 5, Firefox 4.0, IE 9, Opera 10.5 and Safari 5
12092 | 
12093 | **Source:** _github.com/ganqqwerty_
12094 | 
12095 | #### Q17: Write a function that would allow you to do this. ⭐⭐
12096 | **Details:**
12097 | ```js
12098 | var addSix = createBase(6);
12099 | addSix(10); // returns 16
12100 | addSix(21); // returns 27
12101 | ```
12102 | 
12103 | **Answer:**
12104 | You can create a closure to keep the value passed to the function `createBase` even after the inner function is returned. The inner function that is being returned is created within an outer function, making it a closure, and it has access to the variables within the outer function, in this case the variable `baseNumber`.
12105 | 
12106 | ```js
12107 | function createBase(baseNumber) {
12108 |   return function(N) {
12109 |     // we are referencing baseNumber here even though it was declared
12110 |     // outside of this function. Closures allow us to do this in JavaScript
12111 |     return baseNumber + N;
12112 |   }
12113 | }
12114 | 
12115 | var addSix = createBase(6);
12116 | addSix(10);
12117 | addSix(21);
12118 | ```
12119 | 
12120 | **Source:** _coderbyte.com_
12121 | 
12122 | #### Q18: How would you check if a number is an integer? ⭐⭐
12123 | **Answer:**
12124 | A very simply way to check if a number is a decimal or integer is to see if there is a remainder left when you divide by 1.
12125 | 
12126 | ```js
12127 | function isInt(num) {
12128 |   return num % 1 === 0;
12129 | }
12130 | 
12131 | console.log(isInt(4)); // true
12132 | console.log(isInt(12.2)); // false
12133 | console.log(isInt(0.3)); // false
12134 | ```
12135 | 
12136 | **Source:** _coderbyte.com_
12137 | 
12138 | #### Q19: What does "use strict" do? ⭐⭐
12139 | **Answer:**
12140 | The `use strict` literal is entered at the top of a JavaScript program or at the top of a function and it helps you write safer JavaScript code by throwing an error if a global variable is created by mistake. For example, the following program will throw an error:
12141 | 
12142 | ```js
12143 | function doSomething(val) {
12144 |   "use strict"; 
12145 |   x = val + 10;
12146 | }`
12147 | ```
12148 | 
12149 | It will throw an error because `x` was not defined and it is being set to some value in the global scope, which isn't allowed with `use strict` The small change below fixes the error being thrown:
12150 | 
12151 | ```js
12152 | function doSomething(val) {
12153 |   "use strict"; 
12154 |   var x = val + 10;
12155 | }
12156 | ```
12157 | 
12158 | **Source:** _coderbyte.com_
12159 | 
12160 | #### Q20: Explain what a callback function is and provide a simple example. ⭐⭐
12161 | **Answer:**
12162 | A `callback` function is a function that is passed to another function as an argument and is executed after some operation has been completed. Below is an example of a simple callback function that logs to the console *after* some operations have been completed.
12163 | 
12164 | ```js
12165 | function modifyArray(arr, callback) {
12166 |   // do something to arr here
12167 |   arr.push(100);
12168 |   // then execute the callback function that was passed
12169 |   callback();
12170 | }
12171 | 
12172 | var arr = [1, 2, 3, 4, 5];
12173 | 
12174 | modifyArray(arr, function() {
12175 |   console.log("array has been modified", arr);
12176 | });
12177 | ```
12178 | 
12179 | **Source:** _coderbyte.com_
12180 | 
12181 | #### Q21: What are some of the advantages/disadvantages of writing JavaScript code in a language that compiles to JavaScript? ⭐⭐
12182 | **Answer:**
12183 | Some examples of languages that compile to JavaScript include CoffeeScript, Elm, ClojureScript, PureScript, and TypeScript.
12184 | 
12185 | Advantages:
12186 | 
12187 | * Fixes some of the longstanding problems in JavaScript and discourages JavaScript anti-patterns.
12188 | * Enables you to write shorter code, by providing some syntactic sugar on top of JavaScript, which I think ES5 lacks, but ES2015 is awesome.
12189 | * Static types are awesome (in the case of TypeScript) for large projects that need to be maintained over time.
12190 | 
12191 | Disadvantages:
12192 | 
12193 | * Require a build/compile process as browsers only run JavaScript and your code will need to be compiled into JavaScript before being served to browsers.
12194 | * Debugging can be a pain if your source maps do not map nicely to your pre-compiled source.
12195 | * Most developers are not familiar with these languages and will need to learn it. There's a ramp up cost involved for your team if you use it for your projects.
12196 | * Smaller community (depends on the language), which means resources, tutorials, libraries, and tooling would be harder to find.
12197 | * IDE/editor support might be lacking.
12198 | * These languages will always be behind the latest JavaScript standard.
12199 | * Developers should be cognizant of what their code is being compiled to — because that is what would actually be running, and that is what matters in the end.
12200 | 
12201 | Practically, ES2015 has vastly improved JavaScript and made it much nicer to write. I don't really see the need for CoffeeScript these days.
12202 | 
12203 | **Source:** _github.com/yangshun_
12204 | 
12205 | #### Q22: Why would you use something like the `load` event? Does this event have disadvantages? Do you know any alternatives, and why would you use those? ⭐⭐
12206 | **Answer:**
12207 | The `load` event fires at the end of the document loading process. At this point, all of the objects in the document are in the DOM, and all the images, scripts, links and sub-frames have finished loading.
12208 | 
12209 | The DOM event `DOMContentLoaded` will fire after the DOM for the page has been constructed, but do not wait for other resources to finish loading. This is preferred in certain cases when you do not need the full page to be loaded before initializing.
12210 | 
12211 | **Source:** _github.com/yangshun_
12212 | 
12213 | #### Q23: Make this work ⭐⭐
12214 | **Details:**
12215 | ```js
12216 | duplicate([1, 2, 3, 4, 5]); // [1,2,3,4,5,1,2,3,4,5]
12217 | ```
12218 | 
12219 | **Answer:**
12220 | ```js
12221 | function duplicate(arr) {
12222 |   return arr.concat(arr);
12223 | }
12224 | 
12225 | duplicate([1, 2, 3, 4, 5]); // [1,2,3,4,5,1,2,3,4,5]
12226 | ```
12227 | 
12228 | **Source:** _github.com/yangshun_
12229 | 
12230 | #### Q24: Explain the same-origin policy with regards to JavaScript. ⭐⭐
12231 | **Answer:**
12232 | The same-origin policy prevents JavaScript from making requests across domain boundaries. An origin is defined as a combination of URI scheme, hostname, and port number. This policy prevents a malicious script on one page from obtaining access to sensitive data on another web page through that page's Document Object Model.
12233 | 
12234 | **Source:** _github.com/yangshun_
12235 | 
12236 | #### Q25: What is the difference between `==` and `===`? ⭐⭐
12237 | **Answer:**
12238 | `==` is the abstract equality operator while `===` is the strict equality operator. The `==` operator will compare for equality after doing any necessary type conversions. The `===` operator will not do type conversion, so if two values are not the same type `===` will simply return `false`. When using `==`, funky things can happen, such as:
12239 | 
12240 | ```js
12241 | 1 == '1'; // true
12242 | 1 == [1]; // true
12243 | 1 == true; // true
12244 | 0 == ''; // true
12245 | 0 == '0'; // true
12246 | 0 == false; // true
12247 | ```
12248 | 
12249 | My advice is never to use the `==` operator, except for convenience when comparing against `null` or `undefined`, where `a == null` will return `true` if `a` is `null` or `undefined`.
12250 | 
12251 | ```js
12252 | var a = null;
12253 | console.log(a == null); // true
12254 | console.log(a == undefined); // true
12255 | ```
12256 | 
12257 | **Source:** _github.com/yangshun_
12258 | 
12259 | #### Q26: Is there anyway to force using strict mode in Node.js? ⭐⭐
12260 | **Answer:**
12261 | you can place
12262 | 
12263 | ```js
12264 | "use strict";
12265 | ```
12266 | 
12267 | at the top of your file in **node >= 0.10.7**, but if you want your whole app to run in strict (**including external modules**) you can do this
12268 | 
12269 | ```sh
12270 | node --use_strict
12271 | ```
12272 | 
12273 | **Source:** _stackoverflow.com_
12274 | 
12275 | #### Q27: How to compare two objects in JavaScript? ⭐⭐⭐
12276 | **Answer:**
12277 | Two non-primitive values, like objects (including function and array) held by reference, so both `==` and `===` comparisons will simply check whether the references match, not anything about the underlying values.
12278 | 
12279 | For example, `arrays` are by default coerced to strings by simply joining all the values with commas (`,`) in between. So two arrays with the same contents would not be `==` equal:
12280 | 
12281 | ```js
12282 | var a = [1,2,3];
12283 | var b = [1,2,3];
12284 | var c = "1,2,3";
12285 | 
12286 | a == c;		// true
12287 | b == c;		// true
12288 | a == b;		// false
12289 | ```
12290 | For *deep object comparison* use external libs like `deep-equal` or implement your own recursive equality algorithm.
12291 | 
12292 | 
12293 | #### Q28: What is the difference between anonymous and named functions?  ⭐⭐⭐
12294 | **Answer:**
12295 | Consider:
12296 | ```js
12297 | var foo = function() { // anonymous function assigned to variable foo
12298 | 	// ..
12299 | };
12300 | 
12301 | var x = function bar(){ // named function (bar) assigned to variable x 
12302 | 	// ..
12303 | };
12304 | 
12305 | foo(); // actual function execution
12306 | x();
12307 | ```
12308 | 
12309 | #### Q29: What is the difference between a shim and a polyfill? ⭐⭐⭐
12310 | **Answer:**
12311 | * A **shim** is any piece of code that performs interception of an API call and provides a layer of abstraction. It isn't necessarily restricted to a web application or HTML5/CSS3.
12312 | 
12313 | * A **polyfill** is a type of shim that retrofits legacy browsers with modern HTML5/CSS3 features usually using Javascript or Flash.
12314 | 
12315 | A shim is a library that brings a new API to an older environment, using only the means of that environment. Thus, a polyfill is a shim for a browser API. 
12316 | 
12317 | **Source:** _stackoverflow.com/_
12318 | 
12319 | #### Q30: Could you explain the difference between ES5 and ES6 ⭐⭐⭐
12320 | **Answer:**
12321 | * **ECMAScript 5 (ES5)**: The 5th edition of ECMAScript, standardized in 2009. This standard has been implemented fairly completely in all modern browsers
12322 | 
12323 | * **ECMAScript 6 (ES6)/ ECMAScript 2015 (ES2015)**: The 6th edition of ECMAScript, standardized in 2015. This standard has been partially implemented in most modern browsers.
12324 | 
12325 | Here are some key differences between ES5 and ES6:
12326 | * **Arrow functions** & **string interpolation**:<br/>
12327 | Consider:
12328 | ```js
12329 | const greetings = (name) => {
12330 |       return `hello ${name}`;
12331 | }
12332 | ```
12333 | and even:
12334 | ```js
12335 | const greetings = name => `hello ${name}`;
12336 | ```
12337 | * **Const**. <br>
12338 | Const works like a constant in other languages in many ways but there are some caveats. Const stands for ‘constant reference’ to a value. So with const, you can actually mutate the properties of an object being referenced by the variable. You just can’t change the reference itself.
12339 | ```js
12340 | const NAMES = [];
12341 | NAMES.push("Jim");
12342 | console.log(NAMES.length === 1); // true
12343 | NAMES = ["Steve", "John"]; // error
12344 | ```
12345 | * **Block-scoped variables**.<br>
12346 | The new ES6 keyword `let` allows developers to scope variables at the block level.
12347 | `Let` doesn’t hoist in the same way `var` does.
12348 | * **Default parameter values**
12349 | Default parameters allow us to initialize functions with default values. A default is used when an argument is either omitted or undefined — meaning null is a valid value.
12350 | ```js
12351 | // Basic syntax
12352 | function multiply (a, b = 2) {
12353 |      return a * b;
12354 | }
12355 | multiply(5); // 10
12356 | ```
12357 | * ** Class Definition and Inheritance**<br>
12358 | ES6 introduces language support for classes (`class` keyword), constructors (`constructor` keyword), and the `extend` keyword for inheritance.
12359 | 
12360 | * **for-of operator**<br>
12361 | The for...of statement creates a loop iterating over iterable objects.
12362 | * **Spread Operator**
12363 | For objects merging
12364 | ```js
12365 | const obj1 = { a: 1, b: 2 }
12366 | const obj2 = { a: 2, c: 3, d: 4}
12367 | const obj3 = {...obj1, ...obj2}
12368 | ```
12369 | * **Promises**<br>
12370 | Promises provide a mechanism to handle the results and errors from asynchronous operations.  You can accomplish the same thing with callbacks, but promises provide improved readability via method chaining and succinct error handling. 
12371 | ```js
12372 | const isGreater = (a, b) => {
12373 |   return new Promise ((resolve, reject) => {
12374 |     if(a > b) {
12375 |       resolve(true)
12376 |     } else {
12377 |       reject(false)
12378 |     }
12379 |     })
12380 | }
12381 | isGreater(1, 2)
12382 |   .then(result => {
12383 |     console.log('greater')
12384 |   })
12385 |  .catch(result => {
12386 |     console.log('smaller')
12387 |  })
12388 | ```
12389 | * **Modules exporting & importing**
12390 | Consider module exporting:
12391 | ```js
12392 | const myModule = { x: 1, y: () => { console.log('This is ES5') }}
12393 | export default myModule;
12394 | ```
12395 | and importing:
12396 | ```js
12397 | import myModule from './myModule';
12398 | ```
12399 | 
12400 | 
12401 | #### Q31: Given an array of integers, find the largest difference between two elements such that the element of lesser value must come before the greater element ⭐⭐⭐
12402 | **Answer:**
12403 | ```js
12404 | var array = [7, 8, 4, 9, 9, 15, 3, 1, 10];
12405 | // [7, 8, 4, 9, 9, 15, 3, 1, 10] would return `11` based on the difference between `4` and `15`
12406 | // Notice: It is not `14` from the difference between `15` and `1` because 15 comes before 1.
12407 | 
12408 | findLargestDifference(array);
12409 | 
12410 | function findLargestDifference(array) {
12411 |   // If there is only one element, there is no difference
12412 |   if (array.length <= 1) return -1;
12413 | 
12414 |   // currentMin will keep track of the current lowest
12415 |   var currentMin = array[0];
12416 |   var currentMaxDifference = 0;
12417 | 
12418 |   // We will iterate through the array and keep track of the current max difference
12419 |   // If we find a greater max difference, we will set the current max difference to that variable
12420 |   // Keep track of the current min as we iterate through the array, since we know the greatest
12421 |   // difference is yield from `largest value in future` - `smallest value before it`
12422 | 
12423 |   for (var i = 1; i < array.length; i++) {
12424 |     if (array[i] > currentMin && (array[i] - currentMin > currentMaxDifference)) {
12425 |       currentMaxDifference = array[i] - currentMin;
12426 |     } else if (array[i] <= currentMin) {
12427 |       currentMin = array[i];
12428 |     }
12429 |   }
12430 | 
12431 |   // If negative or 0, there is no largest difference
12432 |   if (currentMaxDifference <= 0) return -1;
12433 | 
12434 |   return currentMaxDifference;
12435 | }
12436 | ```
12437 | 
12438 | **Source:** _https://github.com/kennymkchan_
12439 | 
12440 | #### Q32: Find the intersection of two arrays. An intersection would be the common elements that exists within both arrays. In this case, these elements should be unique! ⭐⭐⭐
12441 | **Answer:**
12442 | ```js
12443 | var firstArray = [2, 2, 4, 1];
12444 | var secondArray = [1, 2, 0, 2];
12445 | 
12446 | intersection(firstArray, secondArray); // [2, 1]
12447 | 
12448 | function intersection(firstArray, secondArray) {
12449 |   // The logic here is to create a hashmap with the elements of the firstArray as the keys.
12450 |   // After that, you can use the hashmap's O(1) look up time to check if the element exists in the hash
12451 |   // If it does exist, add that element to the new array.
12452 | 
12453 |   var hashmap = {};
12454 |   var intersectionArray = [];
12455 | 
12456 |   firstArray.forEach(function(element) {
12457 |     hashmap[element] = 1;
12458 |   });
12459 | 
12460 |   // Since we only want to push unique elements in our case... we can implement a counter to keep track of what we already added
12461 |   secondArray.forEach(function(element) {
12462 |     if (hashmap[element] === 1) {
12463 |       intersectionArray.push(element);
12464 |       hashmap[element]++;
12465 |     }
12466 |   });
12467 | 
12468 |   return intersectionArray;
12469 | 
12470 |   // Time complexity O(n), Space complexity O(n)
12471 | }
12472 | ```
12473 | 
12474 | **Source:** _https://github.com/kennymkchan_
12475 | 
12476 | #### Q33: Given two strings, return true if they are anagrams of one another ⭐⭐⭐
12477 | **Details:**
12478 | For example: `Mary` is an anagram of `Army`
12479 | 
12480 | **Answer:**
12481 | ```js
12482 | var firstWord = "Mary";
12483 | var secondWord = "Army";
12484 | 
12485 | isAnagram(firstWord, secondWord); // true
12486 | 
12487 | function isAnagram(first, second) {
12488 |   // For case insensitivity, change both words to lowercase.
12489 |   var a = first.toLowerCase();
12490 |   var b = second.toLowerCase();
12491 | 
12492 |   // Sort the strings, and join the resulting array to a string. Compare the results
12493 |   a = a.split("").sort().join("");
12494 |   b = b.split("").sort().join("");
12495 | 
12496 |   return a === b;
12497 | }
12498 | ```
12499 | 
12500 | **Source:** _https://github.com/kennymkchan_
12501 | 
12502 | #### Q34: Explain the difference between "undefined" and "not defined" in JavaScript ⭐⭐⭐
12503 | **Answer:**
12504 | In JavaScript if you try to use a variable that doesn't exist and has not been declared, then JavaScript will throw an error `var name is not defined` and the script will stop execute thereafter. But If you use `typeof undeclared_variable` then it will return `undefined`.
12505 | 
12506 | Before starting further discussion let's understand the difference between declaration and definition.
12507 | 
12508 | `var x` is a declaration because you are not defining what value it holds yet, but you are declaring its existence and the need of memory allocation.
12509 | 
12510 | ```javascript
12511 | var x; // declaring x
12512 | console.log(x); //output: undefined
12513 | ```
12514 | 
12515 | `var x = 1` is both declaration and definition (also we can say we are doing initialisation), Here declaration and assignment of value happen inline for variable x, In JavaScript every variable declaration and function declaration brings to the top of its current scope in which it's declared then assignment happen in order this term is called `hoisting`.
12516 | 
12517 | A variable that is declared but not define and when we try to access it, It will result `undefined`.
12518 | 
12519 | ```javascript
12520 | var x; // Declaration
12521 | if(typeof x === 'undefined') // Will return true
12522 | ```
12523 | 
12524 | > A variable that neither declared nor defined when we try to reference such variable then It result `not defined`.
12525 | 
12526 | ```javascript
12527 | console.log(y);  // Output: ReferenceError: y is not defined
12528 | ```
12529 | 
12530 | **Source:** _stackoverflow.com_
12531 | 
12532 | #### Q35: What is the drawback of creating true private in JavaScript? ⭐⭐⭐
12533 | **Answer:**
12534 | One of the drawback of creating a true private method in JavaScript is that they are very memory inefficient because a new copy of the method would be created for each instance.
12535 | 
12536 | ```javascript
12537 | var Employee = function (name, company, salary) {
12538 |   this.name = name || "";       //Public attribute default value is null
12539 |   this.company = company || ""; //Public attribute default value is null
12540 |   this.salary = salary || 5000; //Public attribute default value is null
12541 | 
12542 |   // Private method
12543 |   var increaseSalary = function () {
12544 |     this.salary = this.salary + 1000;
12545 |   };
12546 | 
12547 |   // Public method
12548 |   this.dispalyIncreasedSalary = function() {
12549 |     increaseSalary();
12550 |     console.log(this.salary);
12551 |   };
12552 | };
12553 | 
12554 | // Create Employee class object
12555 | var emp1 = new Employee("John","Pluto",3000);
12556 | // Create Employee class object
12557 | var emp2 = new Employee("Merry","Pluto",2000);
12558 | // Create Employee class object
12559 | var emp3 = new Employee("Ren","Pluto",2500);
12560 | ```
12561 | 
12562 | Here each instance variable `emp1`, `emp2`, `emp3` has own copy of increaseSalary private method.
12563 | 
12564 | So as recommendation don't go for a private method unless it's necessary.
12565 | 
12566 | **Source:** _github.com/ganqqwerty_
12567 | 
12568 | #### Q36: What will be the output of the following code? ⭐⭐⭐
12569 | **Details:**
12570 | ```javascript
12571 | var x = 1;
12572 | var output = (function() {
12573 |   delete x;
12574 |   return x;
12575 | })();
12576 | 
12577 | console.log(output);
12578 | ```
12579 | 
12580 | **Answer:**
12581 | Above code will output `1` as output. `delete` operator is used to delete property from object. Here `x` is not an object it's **global variable** of type `number`.
12582 | 
12583 | 
12584 | **Source:** _github.com/ganqqwerty_
12585 | 
12586 | #### Q37: What is IIFEs (Immediately Invoked Function Expressions)? ⭐⭐⭐
12587 | **Answer:**
12588 | It’s an Immediately-Invoked Function Expression, or IIFE for short. It executes immediately after it’s created:
12589 | ```js
12590 | (function IIFE(){
12591 | 	console.log( "Hello!" );
12592 | })();
12593 | // "Hello!"
12594 | ```
12595 | 
12596 | This pattern is often used when trying to avoid polluting the global namespace, because all the variables used inside the IIFE (like in any other normal function) are not visible outside its scope.
12597 | 
12598 | **Source:** _stackoverflow.com_
12599 | 
12600 | #### Q38: Write a function that would allow you to do this ⭐⭐⭐
12601 | **Details:**
12602 | ```js
12603 | multiply(5)(6);
12604 | ```
12605 | 
12606 | **Answer:**
12607 | You can create a *closure* to keep the value of a even after the inner function is returned. The inner function that is being returned is created within an outer function, making it a closure, and it has access to the variables within the outer function, in this case the variable `a`.
12608 | 
12609 | ```js
12610 | function multiply(a) {
12611 |   return function(b) {
12612 |     return a * b;
12613 |   }
12614 | }
12615 | 
12616 | multiply(5)(6);
12617 | ```
12618 | 
12619 | 
12620 | 
12621 | **Source:** _coderbyte.com_
12622 | 
12623 | #### Q39: What's the difference between using “let” and “var” to declare a variable in ES6? ⭐⭐⭐
12624 | **Answer:**
12625 | The difference is _scoping_. `var` is scoped to the nearest function block and `let` is scoped to the nearest enclosing block, which can be smaller than a function block. Both are global if outside any block. Also, variables declared with `let` are not accessible before they are declared in their enclosing block. This will throw a `ReferenceError` exception.
12626 | 
12627 | **Source:** _stackoverflow.com_
12628 | 
12629 | #### Q40: What are the benefits of using spread syntax in ES6 and how is it different from rest syntax? ⭐⭐⭐
12630 | **Answer:**
12631 | ES6's spread syntax is very useful when coding in a functional paradigm as we can easily create copies of arrays or objects without resorting to `Object.create`, `slice`, or a library function. This language feature is used often in Redux and rx.js projects.
12632 | 
12633 | ```js
12634 | function putDookieInAnyArray(arr) {
12635 |   return [...arr, 'dookie'];
12636 | }
12637 | 
12638 | const result = putDookieInAnyArray(['I', 'really', "don't", 'like']); // ["I", "really", "don't", "like", "dookie"]
12639 | 
12640 | const person = {
12641 |   name: 'Todd',
12642 |   age: 29,
12643 | };
12644 | 
12645 | const copyOfTodd = { ...person };
12646 | ```
12647 | 
12648 | ES6's rest syntax offers a shorthand for including an arbitrary number of arguments to be passed to a function. It is like an inverse of the spread syntax, taking data and stuffing it into an array rather than unpacking an array of data, and it works in function arguments, as well as in array and object destructuring assignments.
12649 | 
12650 | ```js
12651 | function addFiveToABunchOfNumbers(...numbers) {
12652 |   return numbers.map(x => x + 5);
12653 | }
12654 | 
12655 | const result = addFiveToABunchOfNumbers(4, 5, 6, 7, 8, 9, 10); // [9, 10, 11, 12, 13, 14, 15]
12656 | 
12657 | const [a, b, ...rest] = [1, 2, 3, 4]; // a: 1, b: 2, rest: [3, 4]
12658 | 
12659 | const { e, f, ...others } = {
12660 |   e: 1,
12661 |   f: 2,
12662 |   g: 3,
12663 |   h: 4,
12664 | }; // e: 1, f: 2, others: { g: 3, h: 4 }
12665 | ```
12666 | 
12667 | **Source:** _github.com/yangshun_
12668 | 
12669 | #### Q41: What is 'Currying'? ⭐⭐⭐
12670 | **Answer:**
12671 | Currying is when you break down a function that takes multiple arguments into a series of functions that take part of the arguments. Here's an example in JavaScript:
12672 | 
12673 | ```js
12674 | function add (a, b) {
12675 |   return a + b;
12676 | }
12677 | 
12678 | add(3, 4); // returns 7
12679 | ```
12680 | 
12681 | This is a function that takes two arguments, a and b, and returns their sum. We will now curry this function:
12682 | 
12683 | ```js
12684 | function add (a) {
12685 |   return function (b) {
12686 |     return a + b;
12687 |   }
12688 | }
12689 | ```
12690 | In an algebra of functions, dealing with functions that take multiple arguments (or equivalent one argument that's an N-tuple) is somewhat inelegant. So how do you deal with something you'd naturally express as, say, f(x,y)? Well, you take that as equivalent to f(x)(y) -- f(x), call it g, is a function, and you apply that function to y. In other words, you only have functions that take one argument -- but some of those functions return other functions (which ALSO take one argument).
12691 | 
12692 | **Source:** _stackoverflow.com_
12693 | 
12694 | #### Q42: What are the differences between ES6 class and ES5 function constructors? ⭐⭐⭐
12695 | **Answer:**
12696 | Let's first look at example of each:
12697 | 
12698 | ```js
12699 | // ES5 Function Constructor
12700 | function Person(name) {
12701 |   this.name = name;
12702 | }
12703 | 
12704 | // ES6 Class
12705 | class Person {
12706 |   constructor(name) {
12707 |     this.name = name;
12708 |   }
12709 | }
12710 | ```
12711 | 
12712 | For simple constructors, they look pretty similar.
12713 | 
12714 | The main difference in the constructor comes when using inheritance. If we want to create a `Student` class that subclasses `Person` and add a `studentId` field, this is what we have to do in addition to the above.
12715 | 
12716 | ```js
12717 | // ES5 Function Constructor
12718 | function Student(name, studentId) {
12719 |   // Call constructor of superclass to initialize superclass-derived members.
12720 |   Person.call(this, name);
12721 | 
12722 |   // Initialize subclass's own members.
12723 |   this.studentId = studentId;
12724 | }
12725 | 
12726 | Student.prototype = Object.create(Person.prototype);
12727 | Student.prototype.constructor = Student;
12728 | 
12729 | // ES6 Class
12730 | class Student extends Person {
12731 |   constructor(name, studentId) {
12732 |     super(name);
12733 |     this.studentId = studentId;
12734 |   }
12735 | }
12736 | ```
12737 | 
12738 | It's much more verbose to use inheritance in ES5 and the ES6 version is easier to understand and remember.
12739 | 
12740 | **Source:** _github.com/yangshun_
12741 | 
12742 | #### Q43: Explain the differences on the usage of `foo` between `function foo() {}` and `var foo = function() {}` ⭐⭐⭐
12743 | **Answer:**
12744 | The former is a _function declaration_ while the latter is a _function expression_. The key difference is that function declarations have its body hoisted but the bodies of function expressions are not (they have the same hoisting behavior as variables). If you try to invoke a function expression before it is defined, you will get an `Uncaught TypeError: XXX is not a function` error.
12745 | 
12746 | **Function Declaration**
12747 | 
12748 | ```js
12749 | foo(); // 'FOOOOO'
12750 | function foo() {
12751 |   console.log('FOOOOO');
12752 | }
12753 | ```
12754 | 
12755 | **Function Expression**
12756 | 
12757 | ```js
12758 | foo(); // Uncaught TypeError: foo is not a function
12759 | var foo = function() {
12760 |   console.log('FOOOOO');
12761 | };
12762 | ```
12763 | 
12764 | **Source:** _github.com/yangshun_
12765 | 
12766 | #### Q44: What are the advantages and disadvantages of using "use strict"? ⭐⭐⭐
12767 | **Answer:**
12768 | 'use strict' is a statement used to enable strict mode to entire scripts or individual functions. Strict mode is a way to opt into a restricted variant of JavaScript.
12769 | 
12770 | Advantages:
12771 | 
12772 | * Makes it impossible to accidentally create global variables.
12773 | * Makes assignments which would otherwise silently fail to throw an exception.
12774 | * Makes attempts to delete undeletable properties throw (where before the attempt would simply have no effect).
12775 | * Requires that function parameter names be unique.
12776 | * `this` is undefined in the global context.
12777 | * It catches some common coding bloopers, throwing exceptions.
12778 | * It disables features that are confusing or poorly thought out.
12779 | 
12780 | Disadvantages:
12781 | 
12782 | * Many missing features that some developers might be used to.
12783 | * No more access to `function.caller` and `function.arguments`.
12784 | * Concatenation of scripts written in different strict modes might cause issues.
12785 | 
12786 | Overall, I think the benefits outweigh the disadvantages, and I never had to rely on the features that strict mode blocks. I would recommend using strict mode.
12787 | 
12788 | 
12789 | **Source:** _github.com/yangshun_
12790 | 
12791 | #### Q45: Explain `Function.prototype.bind`. ⭐⭐⭐
12792 | **Answer:**
12793 | Taken word-for-word from [MDN](https://developer.mozilla.org/en/docs/Web/JavaScript/Reference/Global_objects/Function/bind):
12794 | 
12795 | > The `bind()` method creates a new function that, when called, has its this keyword set to the provided value, with a given sequence of arguments preceding any provided when the new function is called.
12796 | 
12797 | In my experience, it is most useful for binding the value of `this` in methods of classes that you want to pass into other functions. This is frequently done in React components.
12798 | 
12799 | **Source:** _github.com/yangshun_
12800 | 
12801 | #### Q46: What's the difference between `.call` and `.apply`? ⭐⭐⭐
12802 | **Answer:**
12803 | Both `.call` and `.apply` are used to invoke functions and the first parameter will be used as the value of `this` within the function. However, `.call` takes in comma-separated arguments as the next arguments while `.apply` takes in an array of arguments as the next argument. An easy way to remember this is C for `call` and comma-separated and A for `apply` and an array of arguments.
12804 | 
12805 | ```js
12806 | function add(a, b) {
12807 |   return a + b;
12808 | }
12809 | 
12810 | console.log(add.call(null, 1, 2)); // 3
12811 | console.log(add.apply(null, [1, 2])); // 3
12812 | ```
12813 | 
12814 | 
12815 | **Source:** _github.com/yangshun_
12816 | 
12817 | #### Q47: What's a typical use case for anonymous functions? ⭐⭐⭐
12818 | **Answer:**
12819 | They can be used in IIFEs to encapsulate some code within a local scope so that variables declared in it do not leak to the global scope.
12820 | 
12821 | ```js
12822 | (function() {
12823 |   // Some code here.
12824 | })();
12825 | ```
12826 | 
12827 | As a callback that is used once and does not need to be used anywhere else. The code will seem more self-contained and readable when handlers are defined right inside the code calling them, rather than having to search elsewhere to find the function body.
12828 | 
12829 | ```js
12830 | setTimeout(function() {
12831 |   console.log('Hello world!');
12832 | }, 1000);
12833 | ```
12834 | 
12835 | Arguments to functional programming constructs or Lodash (similar to callbacks).
12836 | 
12837 | ```js
12838 | const arr = [1, 2, 3];
12839 | const double = arr.map(function(el) {
12840 |   return el * 2;
12841 | });
12842 | console.log(double); // [2, 4, 6]
12843 | ```
12844 | 
12845 | **Source:** _github.com/yangshun_
12846 | 
12847 | #### Q48: What do you think of AMD vs CommonJS? ⭐⭐⭐
12848 | **Answer:**
12849 | Both are ways to implement a module system, which was not natively present in JavaScript until ES2015 came along. CommonJS is synchronous while AMD (Asynchronous Module Definition) is obviously asynchronous. CommonJS is designed with server-side development in mind while AMD, with its support for asynchronous loading of modules, is more intended for browsers.
12850 | 
12851 | I find AMD syntax to be quite verbose and CommonJS is closer to the style you would write import statements in other languages. Most of the time, I find AMD unnecessary, because if you served all your JavaScript into one concatenated bundle file, you wouldn't benefit from the async loading properties. Also, CommonJS syntax is closer to Node style of writing modules and there is less context-switching overhead when switching between client side and server side JavaScript development.
12852 | 
12853 | I'm glad that with ES2015 modules, that has support for both synchronous and asynchronous loading, we can finally just stick to one approach. Although it hasn't been fully rolled out in browsers and in Node, we can always use transpilers to convert our code.
12854 | 
12855 | **Source:** _github.com/yangshun_
12856 | 
12857 | #### Q49: Why should we use ES6 classes? ⭐⭐⭐
12858 | **Answer:**
12859 | Some reasons you might choose to use **Classes**:
12860 | 
12861 | * The syntax is simpler and less error-prone.
12862 | * It's **much** easier (and again, less error-prone) to set up inheritance hierarchies using the new syntax than with the old.
12863 | * `class` defends you from the common error of failing to use `new` with the constructor function (by having the constructor throw an exception if `this` isn't a valid object for the constructor).
12864 | * Calling the parent prototype's version of a method is much simpler with the new syntax than the old (`super.method()` instead of `ParentConstructor.prototype.method.call(this)` or `Object.getPrototypeOf(Object.getPrototypeOf(this)).method.call(this)`).
12865 | 
12866 | Consider:
12867 | ```js
12868 | // **ES5**
12869 | var Person = function(first, last) {
12870 |     if (!(this instanceof Person)) {
12871 |         throw new Error("Person is a constructor function, use new with it");
12872 |     }
12873 |     this.first = first;
12874 |     this.last = last;
12875 | };
12876 | 
12877 | Person.prototype.personMethod = function() {
12878 |     return "Result from personMethod: this.first = " + this.first + ", this.last = " + this.last;
12879 | };
12880 | 
12881 | var Employee = function(first, last, position) {
12882 |     if (!(this instanceof Employee)) {
12883 |         throw new Error("Employee is a constructor function, use new with it");
12884 |     }
12885 |     Person.call(this, first, last);
12886 |     this.position = position;
12887 | };
12888 | Employee.prototype = Object.create(Person.prototype);
12889 | Employee.prototype.constructor = Employee;
12890 | Employee.prototype.personMethod = function() {
12891 |     var result = Person.prototype.personMethod.call(this);
12892 |     return result + ", this.position = " + this.position;
12893 | };
12894 | Employee.prototype.employeeMethod = function() {
12895 |     // ...
12896 | };
12897 | ```
12898 | And the same with ES6 classes:
12899 | ```js
12900 | // ***ES2015+**
12901 | class Person {
12902 |     constructor(first, last) {
12903 |         this.first = first;
12904 |         this.last = last;
12905 |     }
12906 | 
12907 |     personMethod() {
12908 |         // ...
12909 |     }
12910 | }
12911 | 
12912 | class Employee extends Person {
12913 |     constructor(first, last, position) {
12914 |         super(first, last);
12915 |         this.position = position;
12916 |     }
12917 | 
12918 |     employeeMethod() {
12919 |         // ...
12920 |     }
12921 | }
12922 | ```
12923 | 
12924 | 
12925 | **Source:** _stackoverflow.com_
12926 | 
12927 | #### Q50: Explain the difference between Object.freeze() vs const ⭐⭐⭐
12928 | **Answer:**
12929 | `const` and `Object.freeze` are two completely different things.
12930 | 
12931 | * `const` applies to **bindings** ("variables"). It creates an immutable binding, i.e. you cannot assign a new value to the binding.
12932 | ```js
12933 | const person = {
12934 |     name: "Leonardo"
12935 | };
12936 | let animal = {
12937 |     species: "snake"
12938 | };
12939 | person = animal; // ERROR "person" is read-only
12940 | ```
12941 | * `Object.freeze` works on **values**, and more specifically, *object values*. It makes an object immutable, i.e. you cannot change its properties.
12942 | ```js
12943 | let person = {
12944 |     name: "Leonardo"
12945 | };
12946 | let animal = {
12947 |     species: "snake"
12948 | };
12949 | Object.freeze(person);
12950 | person.name = "Lima"; //TypeError: Cannot assign to read only property 'name' of object
12951 | console.log(person);
12952 | ```
12953 | 
12954 | **Source:** _stackoverflow.com_
12955 | 
12956 | #### Q51: What is generator in JS? ⭐⭐⭐
12957 | **Answer:**
12958 | Generators are functions which can be exited and later re-entered. Their context (variable bindings) will be saved across re-entrances. Generator functions are written using the `function*` syntax. When called initially, generator functions do not execute any of their code, instead returning a type of iterator called a Generator. When a value is consumed by calling the generator's `next` method, the Generator function executes until it encounters the `yield` keyword.
12959 | 
12960 | The function can be called as many times as desired and returns a new Generator each time, however each Generator may only be iterated once.
12961 | 
12962 | ```js
12963 | function* makeRangeIterator(start = 0, end = Infinity, step = 1) {
12964 |     let iterationCount = 0;
12965 |     for (let i = start; i < end; i += step) {
12966 |         iterationCount++;
12967 |         yield i;
12968 |     }
12969 |     return iterationCount;
12970 | }
12971 | ```
12972 | 
12973 | **Source:** _stackoverflow.com_
12974 | 
12975 | #### Q52: When should we use generators in ES6? ⭐⭐⭐
12976 | **Answer:**
12977 | To put it simple, generator has two features:
12978 | 
12979 | * one can choose to jump out of a function and let outer code to determine when to jump back into the function.
12980 | * the control of asynchronous call can be done outside of your code
12981 | 
12982 | The most important feature in generators — we can get the next value in only when we really need it, not all the values at once. And in some situations it can be very convenient.
12983 | 
12984 | **Source:** _stackoverflow.com_
12985 | 
12986 | #### Q53: What is Hoisting in JavaScript? ⭐⭐⭐⭐
12987 | **Answer:**
12988 | Read Full Answer on 👉 <a href='https://www.fullstack.cafe\blog\javascript-interview-questions-and-answers'>FullStack.Cafe</a>
12989 | 
12990 | #### Q54: How does the “this” keyword work? Provide some code examples. ⭐⭐⭐⭐
12991 | **Answer:**
12992 | Read Full Answer on 👉 <a href='https://www.fullstack.cafe\blog\javascript-interview-questions-and-answers'>FullStack.Cafe</a>
12993 | 
12994 | #### Q55: What does the term "Transpiling" stand for? ⭐⭐⭐⭐
12995 | **Answer:**
12996 | Read Full Answer on 👉 <a href='https://www.fullstack.cafe\blog\javascript-interview-questions-and-answers'>FullStack.Cafe</a>
12997 | 
12998 | #### Q56: Check if a given string is a isomorphic ⭐⭐⭐⭐
12999 | **Answer:**
13000 | Read Full Answer on 👉 <a href='https://www.fullstack.cafe\blog\javascript-interview-questions-and-answers'>FullStack.Cafe</a>
13001 | 
13002 | #### Q57: Write a recursive function that performs a binary search ⭐⭐⭐⭐
13003 | **Answer:**
13004 | Read Full Answer on 👉 <a href='https://www.fullstack.cafe\blog\javascript-interview-questions-and-answers'>FullStack.Cafe</a>
13005 | 
13006 | #### Q58: Given an integer, determine if it is a power of 2. If so, return that number, else return -1 ⭐⭐⭐⭐
13007 | **Answer:**
13008 | Read Full Answer on 👉 <a href='https://www.fullstack.cafe\blog\javascript-interview-questions-and-answers'>FullStack.Cafe</a>
13009 | 
13010 | #### Q59: What is “closure” in javascript? Provide an example? ⭐⭐⭐⭐
13011 | **Answer:**
13012 | Read Full Answer on 👉 <a href='https://www.fullstack.cafe\blog\javascript-interview-questions-and-answers'>FullStack.Cafe</a>
13013 | 
13014 | #### Q60: What will be the output of the following code? ⭐⭐⭐⭐
13015 | **Details:**
13016 | ```javascript
13017 | var Employee = {
13018 |   company: 'xyz'
13019 | }
13020 | var emp1 = Object.create(Employee);
13021 | delete emp1.company
13022 | console.log(emp1.company);
13023 | ```
13024 | 
13025 | **Answer:**
13026 | Read Full Answer on 👉 <a href='https://www.fullstack.cafe\blog\javascript-interview-questions-and-answers'>FullStack.Cafe</a>
13027 | 
13028 | #### Q61: Explain the Prototype Design Pattern ⭐⭐⭐⭐
13029 | **Answer:**
13030 | Read Full Answer on 👉 <a href='https://www.fullstack.cafe\blog\javascript-interview-questions-and-answers'>FullStack.Cafe</a>
13031 | 
13032 | #### Q62: How would you add your own method to the Array object so the following code would work? ⭐⭐⭐⭐
13033 | **Details:**
13034 | ```js
13035 | var arr = [1, 2, 3, 4, 5];
13036 | var avg = arr.average();
13037 | console.log(avg);
13038 | ```
13039 | 
13040 | **Answer:**
13041 | Read Full Answer on 👉 <a href='https://www.fullstack.cafe\blog\javascript-interview-questions-and-answers'>FullStack.Cafe</a>
13042 | 
13043 | #### Q63: What will the following code output? ⭐⭐⭐⭐
13044 | **Details:**
13045 | ```js
13046 | 0.1 + 0.2 === 0.3
13047 | ```
13048 | 
13049 | **Answer:**
13050 | Read Full Answer on 👉 <a href='https://www.fullstack.cafe\blog\javascript-interview-questions-and-answers'>FullStack.Cafe</a>
13051 | 
13052 | #### Q64: How would you create a private variable in JavaScript? ⭐⭐⭐⭐
13053 | **Answer:**
13054 | Read Full Answer on 👉 <a href='https://www.fullstack.cafe\blog\javascript-interview-questions-and-answers'>FullStack.Cafe</a>
13055 | 
13056 | #### Q65: What are the actual uses of ES6 WeakMap? ⭐⭐⭐⭐
13057 | **Answer:**
13058 | Read Full Answer on 👉 <a href='https://www.fullstack.cafe\blog\javascript-interview-questions-and-answers'>FullStack.Cafe</a>
13059 | 
13060 | #### Q66: Can you give an example for destructuring an object or an array in ES6? ⭐⭐⭐⭐
13061 | **Answer:**
13062 | Read Full Answer on 👉 <a href='https://www.fullstack.cafe\blog\javascript-interview-questions-and-answers'>FullStack.Cafe</a>
13063 | 
13064 | #### Q67: Explain difference between: `function Person(){}`, `var person = Person()`, and `var person = new Person()`? ⭐⭐⭐⭐
13065 | **Answer:**
13066 | Read Full Answer on 👉 <a href='https://www.fullstack.cafe\blog\javascript-interview-questions-and-answers'>FullStack.Cafe</a>
13067 | 
13068 | #### Q68: What's the difference between a variable that is: `null`, `undefined` or undeclared? How would you go about checking for any of these states? ⭐⭐⭐⭐
13069 | **Answer:**
13070 | Read Full Answer on 👉 <a href='https://www.fullstack.cafe\blog\javascript-interview-questions-and-answers'>FullStack.Cafe</a>
13071 | 
13072 | #### Q69: Explain why the following doesn't work as an IIFE. What needs to be changed to properly make it an IIFE? ⭐⭐⭐⭐
13073 | **Details:**
13074 | ```js
13075 | function foo(){ }();
13076 | ```
13077 | 
13078 | **Answer:**
13079 | Read Full Answer on 👉 <a href='https://www.fullstack.cafe\blog\javascript-interview-questions-and-answers'>FullStack.Cafe</a>
13080 | 
13081 | #### Q70: Describe the Revealing Module Pattern design pattern ⭐⭐⭐⭐⭐
13082 | **Answer:**
13083 | Read Full Answer on 👉 <a href='https://www.fullstack.cafe\blog\javascript-interview-questions-and-answers'>FullStack.Cafe</a>
13084 | 
13085 | #### Q71: Can you give an example of a curry function and why this syntax offers an advantage? ⭐⭐⭐⭐⭐
13086 | **Answer:**
13087 | Read Full Answer on 👉 <a href='https://www.fullstack.cafe\blog\javascript-interview-questions-and-answers'>FullStack.Cafe</a>
13088 | 
13089 | #### Q72: How to "deep-freeze" object in JavaScript? ⭐⭐⭐⭐⭐
13090 | **Answer:**
13091 | Read Full Answer on 👉 <a href='https://www.fullstack.cafe\blog\javascript-interview-questions-and-answers'>FullStack.Cafe</a>
13092 | 
13093 | #### Q73: What is the difference between the await keyword and the yield keyword?  ⭐⭐⭐⭐⭐
13094 | **Answer:**
13095 | Read Full Answer on 👉 <a href='https://www.fullstack.cafe\blog\javascript-interview-questions-and-answers'>FullStack.Cafe</a>
13096 | 
13097 | #### Q74: Is it possible to reset an ECMAScript 6 generator to its initial state? ⭐⭐⭐⭐⭐
13098 | **Answer:**
13099 | Read Full Answer on 👉 <a href='https://www.fullstack.cafe\blog\javascript-interview-questions-and-answers'>FullStack.Cafe</a>
13100 | 
13101 | #### Q75: Compare Async/Await and Generators usage to achive same functionality ⭐⭐⭐⭐⭐
13102 | **Answer:**
13103 | Read Full Answer on 👉 <a href='https://www.fullstack.cafe\blog\javascript-interview-questions-and-answers'>FullStack.Cafe</a>
13104 | 
13105 | ## [[⬆]](#toc) <a name=8CommonFullStackInterviewQuestionsToBrushUp(2018Edition)>8 Common Full Stack Interview Questions To Brush Up (2018 Edition)</a>
13106 | > Originally published on 👉 <a href='https://www.fullstack.cafe\blog\8-ultimate-full-stack-interview-questions-and-answers'>8 Common Full Stack Interview Questions To Brush Up (2018 Edition) | FullStack.Cafe</a>
13107 | 
13108 | #### Q1: What is Inversion of Control? ⭐⭐
13109 | **Answer:**
13110 | 
13111 | *Inversion of control* is a broad term but for a software developer it's most commonly described as a pattern used for decoupling components and layers in the system. 
13112 | 
13113 | For example, say your application has a text editor component and you want to provide spell checking. Your standard code would look something like this:
13114 | ```js
13115 | public class TextEditor {
13116 | 
13117 |     private SpellChecker checker;
13118 | 
13119 |     public TextEditor() {
13120 |         this.checker = new SpellChecker();
13121 |     }
13122 | }
13123 | ```
13124 | What we've done here creates a dependency between the TextEditor and the SpellChecker. In an IoC scenario we would instead do something like this:
13125 | ```js
13126 | public class TextEditor {
13127 | 
13128 |     private IocSpellChecker checker;
13129 | 
13130 |     public TextEditor(IocSpellChecker checker) {
13131 |         this.checker = checker;
13132 |     }
13133 | }
13134 | ```
13135 | 
13136 | You have *inverted control* by handing the responsibility of instantiating the spell checker from the TextEditor class to the caller.
13137 | 
13138 | ```js
13139 | SpellChecker sc = new SpellChecker; // dependency
13140 | TextEditor textEditor = new TextEditor(sc);
13141 | ```
13142 | 
13143 | 
13144 | **Source:** _stackoverflow.com_
13145 | 
13146 | #### Q2: What is Bridge pattern? ⭐⭐⭐
13147 | **Answer:**
13148 | **Bridge pattern** is used when we need to decouple an abstraction from its implementation so that the two can vary independently. This type of design pattern comes under *structural* pattern as this pattern decouples implementation class and abstract class by providing a bridge structure between them.
13149 | 
13150 | The bridge pattern is useful when both the class and what it does vary often. The class itself can be thought of as the abstraction and what the class can do as the implementation. The bridge pattern can also be thought of as two layers of abstraction.
13151 | 
13152 | <div class="text-center">
13153 | <img src="http://www.bogotobogo.com/DesignPatterns/images/bridge/bridgediagram.png" class="img-fluid">
13154 | </div>
13155 | 
13156 | This pattern involves an interface which acts as a bridge which makes the functionality of concrete classes independent from interface implementer classes. Both types of classes can be altered structurally without affecting each other.
13157 | 
13158 | The example of bridge pattern implementation is when:
13159 | ```sh
13160 |                    ----Shape---
13161 |                   /            \
13162 |          Rectangle              Circle
13163 |         /         \            /      \
13164 | BlueRectangle  RedRectangle BlueCircle RedCircle
13165 | ```
13166 | refactored to:
13167 | ```sh
13168 |           ----Shape---                        Color
13169 |          /            \                       /   \
13170 | Rectangle(Color)   Circle(Color)           Blue   Red
13171 | ```
13172 | or in general when:
13173 | ```sh
13174 |         A
13175 |      /     \
13176 |     Aa      Ab
13177 |    / \     /  \
13178 |  Aa1 Aa2  Ab1 Ab2
13179 | ```
13180 | refactored to:
13181 | ```sh
13182 |      A         N
13183 |   /     \     / \
13184 | Aa(N) Ab(N)  1   2
13185 | ```
13186 | 
13187 | **Source:** _tutorialspoint.com_
13188 | 
13189 | #### Q3: What are the success factors for Continuous Integration? ⭐⭐
13190 | **Answer:**
13191 | *   Maintain a code repository
13192 | *   Automate the build
13193 | *   Make the build self-testing
13194 | *   Everyone commits to the baseline every day
13195 | *   Every commit (to baseline) should be built
13196 | *   Keep the build fast
13197 | *   Test in a clone of the production environment
13198 | *   Make it easy to get the latest deliverables
13199 | *   Everyone can see the results of the latest build
13200 | *   Automate deployment
13201 | 
13202 | **Source:** _edureka.co_
13203 | 
13204 | #### Q4: Explain a use case for Docker ⭐⭐⭐
13205 | **Answer:**
13206 | * Docker a low overhead way to run virtual machines on your local box or in the cloud. Although they're not strictly distinct machines, nor do they need to boot an OS, they give you many of those benefits.
13207 | * Docker can encapsulate legacy applications, allowing you to deploy them to servers that might not otherwise be easy to setup with older packages & software versions.
13208 | * Docker can be used to build test boxes, during your deploy process to facilitate continuous integration testing.
13209 | * Docker can be used to provision boxes in the cloud, and with swarm you can orchestrate clusters too.
13210 | 
13211 | **Source:** _dev.to_
13212 | 
13213 | #### Q5: Can you explain what “git reset” does in plain english? ⭐⭐⭐⭐
13214 | **Answer:**
13215 | Read Full Answer on 👉 <a href='https://www.fullstack.cafe\blog\8-ultimate-full-stack-interview-questions-and-answers'>FullStack.Cafe</a>
13216 | 
13217 | #### Q6: Explain the main difference between REST and GraphQL ⭐⭐⭐
13218 | **Answer:**
13219 | The main and most important difference between REST and GraphQL is that *GraphQL is not dealing with dedicated resources, instead everything is regarded as a graph and therefore is connected and can be queried to app exact needs*.
13220 | 
13221 | **Source:** _medium.com/codingthesmartway-com-blog_
13222 | 
13223 | #### Q7: Explain prototype inheritance in JavaScript? ⭐⭐⭐⭐
13224 | **Answer:**
13225 | Read Full Answer on 👉 <a href='https://www.fullstack.cafe\blog\8-ultimate-full-stack-interview-questions-and-answers'>FullStack.Cafe</a>
13226 | 
13227 | #### Q8: What is Event Loop? ⭐⭐⭐
13228 | **Answer:**
13229 | Node.js is a single threaded application but it support concurrency via concept of event and callbacks. As every API of Node js are asynchronous and being a single thread, it uses async function calls to maintain the concurrency. Node uses observer pattern. Node thread keeps an event loop and whenever any task get completed, it fires the corresponding event which signals the event listener function to get executed.
13230 | 
13231 | **Source:** _tutorialspoint.com_
13232 | 
13233 | ## [[⬆]](#toc) <a name=8DevOpsInterviewQuestionsandAnswersin2018>8 DevOps Interview Questions and Answers in 2018</a>
13234 | > Originally published on 👉 <a href='https://www.fullstack.cafe\blog\8-devops-interview-questions-and-answers-2018'>8 DevOps Interview Questions and Answers in 2018 | FullStack.Cafe</a>
13235 | 
13236 | #### Q1: Explain what is DevOps ? ⭐
13237 | **Answer:**
13238 | **DevOps** is a newly emerging term in IT field, which is nothing but a practice that emphasizes the collaboration and communication of both software developers and other information-technology (IT) professionals. It focuses on delivering software product faster and lowering the failure rate of releases.
13239 | 
13240 | **Source:** _quora.com_
13241 | 
13242 | #### Q2: How is DevOps different from Agile/SDLC? ⭐⭐
13243 | **Answer:**
13244 | * Agile software development methodology focuses on the development of software.
13245 | * DevOps on the other hand is responsible for development as well as deployment of the software in the safest and most reliable way possible.
13246 | 
13247 | 
13248 | **Source:** _edureka.co_
13249 | 
13250 | #### Q3: What does Containerization mean? ⭐⭐
13251 | **Answer:**
13252 | *Containerisation* is a type of *virtualization* strategy that emerged as an alternative to traditional hypervisor-based virtualization. 
13253 | 
13254 | In containerization, the operating system is shared by the different containers rather than cloned for each virtual machine. For example Docker provides a container virtualization platform that serves as a good alternative to hypervisor-based arrangements.
13255 | 
13256 | **Source:** _linoxide.com_
13257 | 
13258 | #### Q4: What is the difference between resource allocation and resource provisioning? ⭐⭐⭐
13259 | **Answer:**
13260 | * Resource allocation is the process of reservation that demarcates a quantity of a resource for a tenant's use.
13261 | * Resource provision is the process of activation of a bundle of the allocated quantity to bear the tenant's workload.
13262 | 
13263 | Immediately after allocation, all the quantity of a resource is available.  Provision removes a quantity of a resource from the available set. De-provision returns a quantity of a resource to the available set.
13264 | At any time:
13265 | 
13266 | ```
13267 | Allocated quantity = Available quantity + Provisioned quantity
13268 | ```
13269 | 
13270 | **Source:** _dev.to_
13271 | 
13272 | #### Q5: Classify Cloud Platforms by category ⭐⭐⭐
13273 | **Answer:**
13274 | Cloud Computing software can be classified as:
13275 | * **Software as a Service or SaaS** - is peace of software that runs over network on remote server and has only user interface exposed to users, usually in web browser. For example salesforce.com.
13276 | * **Infrastructure as a Service or IaaS** -  is a cloud environment that exposes VM to user to use as entire OS or container where you could install anything you would install on your server. Example for this would be OpenStack, AWS, Eucalyptus.  
13277 | * **Platform as a Service or PaaS** - allows users to deploy their own application on the preinstalled platform, usually framework of application server and suite of developer tools. Examples for this would be Heroku.
13278 | 
13279 | **Source:** _linoxide.com_
13280 | 
13281 | #### Q6: How is container different from a virtual machine? ⭐⭐⭐⭐
13282 | **Answer:**
13283 | Read Full Answer on 👉 <a href='https://www.fullstack.cafe\blog\8-devops-interview-questions-and-answers-2018'>FullStack.Cafe</a>
13284 | 
13285 | #### Q7: Are you familiar with The Twelve-Factor App principles? ⭐⭐⭐⭐⭐
13286 | **Answer:**
13287 | Read Full Answer on 👉 <a href='https://www.fullstack.cafe\blog\8-devops-interview-questions-and-answers-2018'>FullStack.Cafe</a>
13288 | 
13289 | ## [[⬆]](#toc) <a name=8GraphQLInterviewQuestionsToKnow(in2018)>8 GraphQL Interview Questions To Know (in 2018)</a>
13290 | > Originally published on 👉 <a href='https://www.fullstack.cafe\blog\5-graphql-interview-questions-you-should-know'>8 GraphQL Interview Questions To Know (in 2018) | FullStack.Cafe</a>
13291 | 
13292 | #### Q1: What is GraphQL? ⭐
13293 | **Answer:**
13294 | GraphQL is a query language created by [Facebook](http://facebook.github.io/) in 2012 which provides a **common interface between the client and the server for data fetching and manipulations**.
13295 | 
13296 | The client asks for various data from the GraphQL server via queries. The response format is described in the query and defined by the client instead of the server: they are called **client‐specified queries**.  
13297 | The structure of the data is not hardcoded as in traditional REST APIs - this makes retrieving data from the server more efficient for the client.
13298 | 
13299 | **Source:** _howtographql.com_
13300 | 
13301 | #### Q2: How to do Error Handling? ⭐⭐
13302 | **Answer:**
13303 | A successful GraphQL query is supposed to return a JSON object with a root field called `"data"`. If the request fails or partially fails (e.g. because the user requesting the data doesn’t have the right access permissions), a second root field called `"errors"` is added to the response:
13304 | ```js
13305 |     {
13306 |       "data": { ... },
13307 |       "errors": [ ... ]
13308 |     }
13309 | ```   
13310 | 
13311 | **Source:** _howtographql.com_
13312 | 
13313 | #### Q3: What is GraphQL schema? ⭐⭐
13314 | **Answer:**
13315 | Every GraphQL server has two core parts that determine how it works: a schema and resolve functions.
13316 | 
13317 | The *schema* is a model of the data that can be fetched through the GraphQL server. It defines what queries clients are allowed to make, what types of data can be fetched from the server, and what the relationships between these types are. 
13318 | 
13319 | Consider:
13320 | 
13321 | ```css
13322 | type Author {
13323 |   id: Int
13324 |   name: String
13325 |   posts: [Post]
13326 | }
13327 | type Post {
13328 |   id: Int
13329 |   title: String
13330 |   text: String
13331 |   author: Author
13332 | }
13333 | type Query {
13334 |   getAuthor(id: Int): Author
13335 |   getPostsByTitle(titleContains: String): [Post]
13336 | }
13337 | schema {
13338 |   query: Query
13339 | }
13340 | ```
13341 | 
13342 | **Source:** _dev-blog.apollodata.com_
13343 | 
13344 | #### Q4: How to do Authentication and Authorization? ⭐⭐⭐
13345 | **Answer:**
13346 | Authentication and authorization are often confused. _Authentication_ describes the process of claiming an _identity_. That’s what you do when you log in to a service with a username and password, you authenticate yourself. _Authorization_ on the other hand describes _permission rules_ that specify the access rights of individual users and user groups to certain parts of the system.
13347 | 
13348 | Authentication in GraphQL can be implemented with common patterns such as [OAuth](https://oauth.net/).
13349 | 
13350 | To implement authorization, it is [recommended](http://graphql.org/learn/authorization/) to delegate any data access logic to the business logic layer and not handle it directly in the GraphQL implementation.
13351 | 
13352 | **Source:** _howtographql.com_
13353 | 
13354 | #### Q5: How to do Server-side Caching? ⭐⭐⭐
13355 | **Answer:**
13356 | One common concern with GraphQL, especially when comparing it to REST, are the difficulties to maintain server-side cache. With REST, it’s easy to cache the data for each endpoint, since it’s sure that the _structure_ of the data will not change.
13357 | 
13358 | With GraphQL on the other hand, it’s not clear what a client will request next, so putting a caching layer right behind the API doesn’t make a lot of sense.
13359 | 
13360 | Server-side caching still is a challenge with GraphQL.
13361 | 
13362 | **Source:** _howtographql.com_
13363 | 
13364 | #### Q6: List the key concepts of the GraphQL query language ⭐⭐⭐
13365 | **Answer:**
13366 | **Key concepts of the GraphQL** query language are:
13367 | 
13368 | *   Hierarchical
13369 | *   Product‐centric
13370 | *   Strong‐typing
13371 | *   Client‐specified queries
13372 | *   Introspective
13373 | 
13374 | **Source:** _blog.risingstack.com_
13375 | 
13376 | #### Q7: Explain the main difference between REST and GraphQL ⭐⭐⭐
13377 | **Answer:**
13378 | The main and most important difference between REST and GraphQL is that *GraphQL is not dealing with dedicated resources, instead everything is regarded as a graph and therefore is connected and can be queried to app exact needs*.
13379 | 
13380 | **Source:** _medium.com/codingthesmartway-com-blog_
13381 | 
13382 | #### Q8: Are there any disadvantages to GraphQL? ⭐⭐⭐⭐
13383 | **Answer:**
13384 | Read Full Answer on 👉 <a href='https://www.fullstack.cafe\blog\5-graphql-interview-questions-you-should-know'>FullStack.Cafe</a>
13385 | 
13386 | ## [[⬆]](#toc) <a name=8PerformanceTestingInterviewQuestions&Answersin2018>8 Performance Testing Interview Questions & Answers in 2018</a>
13387 | > Originally published on 👉 <a href='https://www.fullstack.cafe\blog\8-performance-testing-interview-questions-and-answers-in-2018'>8 Performance Testing Interview Questions & Answers in 2018 | FullStack.Cafe</a>
13388 | 
13389 | ## [[⬆]](#toc) <a name=8StepstoIncreaseYourDevResumeResponseRateby90%>8 Steps to Increase Your Dev Resume Response Rate by 90%</a>
13390 | > Originally published on 👉 <a href='https://www.fullstack.cafe\blog\full-stack-resume-template'>8 Steps to Increase Your Dev Resume Response Rate by 90% | FullStack.Cafe</a>
13391 | 
13392 | #### Q1: career test ⭐⭐⭐
13393 | **Details:**
13394 | test
13395 | 
13396 | **Answer:**
13397 | test
13398 | 
13399 | ## [[⬆]](#toc) <a name=9BasicwebpackInterviewQuestionsAndAnswersin2019>9 Basic webpack Interview Questions And Answers in 2019</a>
13400 | > Originally published on 👉 <a href='https://www.fullstack.cafe\blog\basic-webpack-interview-questions-and-answers-2019'>9 Basic webpack Interview Questions And Answers in 2019 | FullStack.Cafe</a>
13401 | 
13402 | #### Q1: What is webpack? ⭐
13403 | **Answer:**
13404 | **Webpack** is a build tool that puts all of your assets, including Javascript, images, fonts, and CSS, in a dependency graph. Webpack lets you use `require()` in your source code to point to local files, like images, and decide how they're processed in your final Javascript bundle, like replacing the path with a URL pointing to a CDN.
13405 | 
13406 | 
13407 | 
13408 | **Source:** _blog.andrewray.me_
13409 | 
13410 | #### Q2: Name some benefits of using webpack ⭐⭐⭐
13411 | **Answer:**
13412 | Webpack and static assets in a dependency graph offers many benefits. Here's a few:
13413 | 
13414 | *   **Dead asset elimination.** This is killer, especially for CSS rules. You only build the images and CSS into your `dist/` folder that your application actually needs.
13415 | *   **Easier code splitting.** For example, because you know that your file `Homepage.js` only requires specific CSS files, Webpack could easily build a `homepage.css` file to greatly reduce initial file size.
13416 | *   **You control how assets are processed.** If an image is below a certain size, you could [base64 encode it](https://developer.mozilla.org/en-US/docs/Web/API/WindowBase64/Base64_encoding_and_decoding) directly into your Javascript for fewer HTTP requests. If a JSON file is too big, you can load it from a URL. You can `require('./style.less')` and it's automaticaly parsed by Less into vanilla CSS.
13417 | *   **Stable production deploys.** You can't accidentally deploy code with images missing, or outdated styles.
13418 | *   Webpack will slow you down at the start, but give you **great speed benefits** when used correctly. You get hot page reloading. True CSS management. CDN cache busting because Webpack automatically changes file names to hashes of the file contents, etc.
13419 | 
13420 | Webpack is the main build tool adopted by the React community.
13421 | 
13422 | **Source:** _blog.andrewray.me_
13423 | 
13424 | #### Q3: Name some plugins you think are very important and helpful ⭐⭐⭐
13425 | **Answer:**
13426 | * **CommonsChunkPlugin** - creates a separate file (known as a chunk), consisting of common modules shared between multiple entry points.
13427 | * **DefinePlugin** -  allows you to create global constants which can be configured at compile time. 
13428 | * **HtmlWebpackPlugin** - simplifies creation of HTML files to serve your webpack bundles. 
13429 | * **ExtractTextWebpackPlugin** - Extract text from a bundle, or bundles, into a separate file.
13430 | * **CompressionWebpackPlugin** - Prepare compressed versions of assets to serve them with Content-Encoding.
13431 | 
13432 | **Source:** _webpack.js.org_
13433 | 
13434 | #### Q4: Webpack gives us a dependency graph. What does that mean? ⭐⭐⭐
13435 | **Answer:**
13436 | Any time one file depends on another, webpack treats this as a *dependency*. This allows webpack to take non-code assets, such as images or web fonts, and also provide them as dependencies for your application.
13437 | 
13438 | Webpack lets you use require() on local "static assets":
13439 | ```js
13440 | <img src={ require('../../assets/logo.png') } />  
13441 | ```
13442 | 
13443 | When webpack processes your application, it starts from a list of modules defined on the command line or in its config file. Starting from these entry points, webpack recursively builds a dependency graph that includes every module your application needs, then packages all of those modules into a small number of bundles - often, just one - to be loaded by the browser.
13444 | 
13445 | The `require('logo.png')` source code never actually gets executed in the browser (nor in Node.js). Webpack builds a new Javascript file, replacing `require()` calls with valid Javascript code, such as URLs. The bundled file is what's executed by Node or the browser.
13446 | 
13447 | **Source:** _blog.andrewray.me_
13448 | 
13449 | #### Q5: List some pitfalls of Webpack ⭐⭐⭐⭐
13450 | **Answer:**
13451 | Read Full Answer on 👉 <a href='https://www.fullstack.cafe\blog\basic-webpack-interview-questions-and-answers-2019'>FullStack.Cafe</a>
13452 | 
13453 | #### Q6: Explain me the difference between NPM vs. Bower vs. Browserify vs. Gulp vs. Grunt vs. Webpack? ⭐⭐⭐⭐
13454 | **Answer:**
13455 | Read Full Answer on 👉 <a href='https://www.fullstack.cafe\blog\basic-webpack-interview-questions-and-answers-2019'>FullStack.Cafe</a>
13456 | 
13457 | #### Q7: What's the difference between webpack loaders and plugins? ⭐⭐⭐⭐
13458 | **Answer:**
13459 | Read Full Answer on 👉 <a href='https://www.fullstack.cafe\blog\basic-webpack-interview-questions-and-answers-2019'>FullStack.Cafe</a>
13460 | 
13461 | #### Q8: Explain this code ⭐⭐⭐⭐
13462 | **Details:**
13463 |  ```javascript
13464 | new webpack.optimize.CommonsChunkPlugin({
13465 |   name: 'common',
13466 |   filename: 'common.js',
13467 |   chunks: ['home', 'dashboard']
13468 | })
13469 |  ```
13470 | 
13471 | **Answer:**
13472 | Read Full Answer on 👉 <a href='https://www.fullstack.cafe\blog\basic-webpack-interview-questions-and-answers-2019'>FullStack.Cafe</a>
13473 | 
13474 | #### Q9: Describe tree shaking mechanism in webpack ⭐⭐⭐⭐⭐
13475 | **Answer:**
13476 | Read Full Answer on 👉 <a href='https://www.fullstack.cafe\blog\basic-webpack-interview-questions-and-answers-2019'>FullStack.Cafe</a>
13477 | 
13478 | ## [[⬆]](#toc) <a name=9ExpertDesignPatternsInterviewQuestionsToKnow(in2018)>9 Expert Design Patterns Interview Questions To Know (in 2018)</a>
13479 | > Originally published on 👉 <a href='https://www.fullstack.cafe\blog\9-unusual-design-patterns-interview-questions'>9 Expert Design Patterns Interview Questions To Know (in 2018) | FullStack.Cafe</a>
13480 | 
13481 | #### Q1: What is Design Patterns and why anyone should use them? ⭐
13482 | **Answer:**
13483 | Design patterns are a well-described solution to the most commonly encountered problems which occur during software development. 
13484 | 
13485 | Design pattern represents the best practices evolved over a period of time by experienced software developers. They promote reusability which leads to a more robust and maintainable code.
13486 | 
13487 | **Source:** _www.educba.com_
13488 | 
13489 | #### Q2: What is Filter pattern? ⭐⭐
13490 | **Answer:**
13491 | **Filter pattern** or **Criteria pattern** is a design pattern that enables developers to filter a set of objects using different criteria and chaining them in a decoupled way through logical operations. This type of design pattern comes under *structural* pattern as this pattern combines multiple criteria to obtain single criteria.
13492 | 
13493 | **Filter design pattern** is useful where you want to add filters dynamically or you are implementing multiple functionalities and most of them require different filter criteria to filter something. In that case instead of hard coding the filters inside the functionalities, you can create filter criteria and re-use it wherever required.
13494 | 
13495 | ```js
13496 | List<Laptop> laptops = LaptopFactory.manufactureInBulk();
13497 | AndCriteria searchCriteria = new AndCriteria(
13498 |   new HardDisk250GBFilter(), 
13499 |   new MacintoshFilter(), 
13500 |   new I5ProcessorFilter());
13501 | List<Laptop> filteredLaptops = searchCriteria.meets(laptops);
13502 | ```
13503 | 
13504 | **Source:** _tutorialspoint.com_
13505 | 
13506 | #### Q3: What is Strategy pattern? ⭐⭐
13507 | **Answer:**
13508 | In **Strategy pattern**, a class behavior or its algorithm can be changed at run time. This type of design pattern comes under _behavior_ pattern.
13509 | 
13510 | In Strategy pattern, we create objects which represent various strategies and a context object whose behavior varies as per its strategy object. The strategy object changes the executing algorithm of the context object.
13511 | 
13512 | <div class="text-center">
13513 | <img src="https://upload.wikimedia.org/wikipedia/commons/4/45/W3sDesign_Strategy_Design_Pattern_UML.jpg" class="img-fluid"/>
13514 | </div>
13515 | 
13516 | 
13517 | 
13518 | **Source:** _tutorialspoint.com_
13519 | 
13520 | #### Q4: What is Observer pattern? ⭐⭐⭐
13521 | **Answer:**
13522 | **Observer pattern**  (also known as *Publish-Subscribe Pattern*) is used when there is one-to-many relationship between objects such as if one object is modified, its dependent objects are to be notified automatically. Observer pattern falls under _behavioral_ pattern category.
13523 | 
13524 | An object with a one-to-many relationship with other objects who are interested in its state is called the _subject_ or _publisher_. The _observers_ are notified whenever the state of the _subject_ changes and can act accordingly. The _subject_ can have any number of dependent _observers_ which it notifies, and any number of _observers_ can subscribe to the _subject_ to receive such notifications.
13525 | 
13526 | Observer pattern uses two actor classes:
13527 | * The Observer (os Subscriber) abstract class provides an `update()` method which will be called by the subject to notify it of the subject’s state change. 
13528 | * The Subject (or Publisher) class is also an abstract class and defines four primary methods: `attach()`, `detach()`, `setState()`, and `notify()`
13529 | 
13530 | 
13531 | 
13532 | <div class="text-center">
13533 | <img src="https://upload.wikimedia.org/wikipedia/commons/0/01/W3sDesign_Observer_Design_Pattern_UML.jpg" class="img-fluid"/>
13534 | </div>
13535 | 
13536 | **Source:** _sitepoint.com_
13537 | 
13538 | #### Q5: When would you use the Builder Pattern? Why not just use a Factory Pattern? ⭐⭐⭐⭐
13539 | **Answer:**
13540 | Read Full Answer on 👉 <a href='https://www.fullstack.cafe\blog\9-unusual-design-patterns-interview-questions'>FullStack.Cafe</a>
13541 | 
13542 | #### Q6: Why would I ever use a Chain of Responsibility over a Decorator? ⭐⭐⭐⭐
13543 | **Answer:**
13544 | Read Full Answer on 👉 <a href='https://www.fullstack.cafe\blog\9-unusual-design-patterns-interview-questions'>FullStack.Cafe</a>
13545 | 
13546 | #### Q7: How is Bridge pattern is different from Adapter pattern? ⭐⭐⭐⭐
13547 | **Answer:**
13548 | Read Full Answer on 👉 <a href='https://www.fullstack.cafe\blog\9-unusual-design-patterns-interview-questions'>FullStack.Cafe</a>
13549 | 
13550 | #### Q8: Explain difference between the Facade, Proxy, Adapter and Decorator design patterns? ⭐⭐⭐⭐⭐
13551 | **Answer:**
13552 | Read Full Answer on 👉 <a href='https://www.fullstack.cafe\blog\9-unusual-design-patterns-interview-questions'>FullStack.Cafe</a>
13553 | 
13554 | #### Q9: What's the difference between the Dependency Injection and Service Locator patterns? ⭐⭐⭐⭐⭐
13555 | **Answer:**
13556 | Read Full Answer on 👉 <a href='https://www.fullstack.cafe\blog\9-unusual-design-patterns-interview-questions'>FullStack.Cafe</a>
13557 | 
13558 | ## [[⬆]](#toc) <a name=9QuestionsEveryDeveloperShouldAskOnInterview>9 Questions Every Developer Should Ask On Interview</a>
13559 | > Originally published on 👉 <a href='https://www.fullstack.cafe\blog\9-questions-every-developer-should-ask-on-interview'>9 Questions Every Developer Should Ask On Interview | FullStack.Cafe</a>
13560 | 
13561 | #### Q1: What does the company do to nurture and train its employees? ⭐⭐
13562 | **Answer:**
13563 | 
13564 | 
13565 | #### Q2: What is your stack? What is the rationale for/story behind this specific stack? ⭐⭐
13566 | **Answer:**
13567 | 
13568 | 
13569 | #### Q3: What is the most fulfilling/exciting/technically complex project that you've worked on here so far? ⭐⭐
13570 | **Answer:**
13571 | 
13572 | 
13573 | #### Q4: What makes your product competitive? ⭐⭐⭐
13574 | **Answer:**
13575 | 
13576 | 
13577 | #### Q5: There's "C++" (or Python, Swift or any other tech) in the job description. How will you estimate my proficiency in this tech in 3 months? ⭐⭐⭐
13578 | **Answer:**
13579 | 
13580 | 
13581 | #### Q6: How much time do you spend on new project development versus maintenance? ⭐⭐⭐⭐
13582 | **Answer:**
13583 | Read Full Answer on 👉 <a href='https://www.fullstack.cafe\blog\9-questions-every-developer-should-ask-on-interview'>FullStack.Cafe</a>
13584 | 
13585 | #### Q7: What has been the worst technical blunder that has happened in the recent past? How did you guys deal with it? What changes were implemented afterwards to make sure it didn't happen again? ⭐⭐⭐⭐
13586 | **Answer:**
13587 | Read Full Answer on 👉 <a href='https://www.fullstack.cafe\blog\9-questions-every-developer-should-ask-on-interview'>FullStack.Cafe</a>
13588 | 
13589 | #### Q8: What is the most costly technical decision made early on that the company is living with now? ⭐⭐⭐⭐
13590 | **Answer:**
13591 | Read Full Answer on 👉 <a href='https://www.fullstack.cafe\blog\9-questions-every-developer-should-ask-on-interview'>FullStack.Cafe</a>
13592 | 
13593 | #### Q9: How long does the average engineer stay at the company? ⭐⭐⭐⭐⭐
13594 | **Answer:**
13595 | Read Full Answer on 👉 <a href='https://www.fullstack.cafe\blog\9-questions-every-developer-should-ask-on-interview'>FullStack.Cafe</a>
13596 | 
13597 | ## [[⬆]](#toc) <a name=9TrickySoftwareArchitectureInterviewQuestions>9 Tricky Software Architecture Interview Questions </a>
13598 | > Originally published on 👉 <a href='https://www.fullstack.cafe\blog\9-tricky-software-architecture-interview-questions'>9 Tricky Software Architecture Interview Questions  | FullStack.Cafe</a>
13599 | 
13600 | #### Q1: What does “program to interfaces, not implementations” mean? ⭐⭐⭐
13601 | **Answer:**
13602 | *Coding against interface* means, the client code always holds an Interface object which is supplied by a *factory*. 
13603 | 
13604 | Any instance returned by the factory would be of type Interface which any factory candidate class must have implemented. This way the client program is not worried about implementation and the interface signature determines what all operations can be done. 
13605 | 
13606 | This approach can be used to change the behavior of a program at run-time. It also helps you to write far better programs from the maintenance point of view.
13607 | 
13608 | **Source:** _tutorialspoint.com_
13609 | 
13610 | #### Q2: What are the differences between continuous integration, continuous delivery, and continuous deployment? ⭐⭐⭐
13611 | **Answer:**
13612 | * Developers practicing **continuous integration** merge their changes back to the main branch as often as possible. By doing so, you avoid the integration hell that usually happens when people wait for release day to merge their changes into the release branch.
13613 | * **Continuous delivery** is an extension of continuous integration to make sure that you can release new changes to your customers quickly in a sustainable way. This means that on top of having automated your testing, you also have automated your release process and you can deploy your application at any point of time by clicking on a button.
13614 | * **Continuous deployment** goes one step further than continuous delivery. With this practice, every change that passes all stages of your production pipeline is released to your customers. There's no human intervention, and only a failed test will prevent a new change to be deployed to production.
13615 | 
13616 | **Source:** _atlassian.com_
13617 | 
13618 | #### Q3: What does SOLID stand for? What are its principles? ⭐⭐⭐
13619 | **Answer:**
13620 | **S.O.L.I.D** is an acronym for the first five object-oriented design (OOD) principles by Robert C. Martin.
13621 | 
13622 | * **S** - *Single-responsiblity principle*. A class should have one and only one reason to change, meaning that a class should have only one job.
13623 | * **O** - *Open-closed principle*. Objects or entities should be open for extension, but closed for modification.
13624 | * **L** - *Liskov substitution principle*. Let q(x) be a property provable about objects of x of type T. Then q(y) should be provable for objects y of type S where S is a subtype of T.
13625 | * **I** - *Interface segregation principle*. A client should never be forced to implement an interface that it doesn't use or clients shouldn't be forced to depend on methods they do not use.
13626 | * **D** - *Dependency Inversion Principle*. Entities must depend on abstractions not on concretions. It states that the high level module must not depend on the low level module, but they should depend on abstractions.
13627 | 
13628 | **Source:** _scotch.io_
13629 | 
13630 | #### Q4: What Is BASE Property Of A System? ⭐⭐⭐⭐
13631 | **Answer:**
13632 | Read Full Answer on 👉 <a href='https://www.fullstack.cafe\blog\9-tricky-software-architecture-interview-questions'>FullStack.Cafe</a>
13633 | 
13634 | #### Q5: What Is CAP Theorem? ⭐⭐⭐⭐⭐
13635 | **Answer:**
13636 | Read Full Answer on 👉 <a href='https://www.fullstack.cafe\blog\9-tricky-software-architecture-interview-questions'>FullStack.Cafe</a>
13637 | 
13638 | #### Q6: Are you familiar with The Twelve-Factor App principles? ⭐⭐⭐⭐⭐
13639 | **Answer:**
13640 | Read Full Answer on 👉 <a href='https://www.fullstack.cafe\blog\9-tricky-software-architecture-interview-questions'>FullStack.Cafe</a>
13641 | 
13642 | #### Q7: What are heuristic exceptions? ⭐⭐⭐⭐⭐
13643 | **Answer:**
13644 | Read Full Answer on 👉 <a href='https://www.fullstack.cafe\blog\9-tricky-software-architecture-interview-questions'>FullStack.Cafe</a>
13645 | 
13646 | #### Q8: What Is Shared Nothing Architecture? How Does It Scale? ⭐⭐⭐⭐⭐
13647 | **Answer:**
13648 | Read Full Answer on 👉 <a href='https://www.fullstack.cafe\blog\9-tricky-software-architecture-interview-questions'>FullStack.Cafe</a>
13649 | 
13650 | #### Q9: What Does Eventually Consistent Mean? ⭐⭐⭐⭐⭐
13651 | **Answer:**
13652 | Read Full Answer on 👉 <a href='https://www.fullstack.cafe\blog\9-tricky-software-architecture-interview-questions'>FullStack.Cafe</a>
13653 | 
13654 | ## [[⬆]](#toc) <a name=AngularDeveloperResumeSample&Template(DownloadWord/PDF)>Angular Developer Resume Sample & Template (Download Word/PDF)</a>
13655 | > Originally published on 👉 <a href='https://www.fullstack.cafe\blog\angular-developer-resume-sample'>Angular Developer Resume Sample & Template (Download Word/PDF) | FullStack.Cafe</a>
13656 | 
13657 | #### Q1: career test ⭐⭐⭐
13658 | **Details:**
13659 | test
13660 | 
13661 | **Answer:**
13662 | test
13663 | 
13664 | ## [[⬆]](#toc) <a name=FrontEndDeveloperResumeSample&Template(Word,PDF)>Front End Developer Resume Sample & Template (Word, PDF)</a>
13665 | > Originally published on 👉 <a href='https://www.fullstack.cafe\blog\front-end-developer-resume-sample'>Front End Developer Resume Sample & Template (Word, PDF) | FullStack.Cafe</a>
13666 | 
13667 | #### Q1: career test ⭐⭐⭐
13668 | **Details:**
13669 | test
13670 | 
13671 | **Answer:**
13672 | test
13673 | 
13674 | ## [[⬆]](#toc) <a name=GuestVoice:TheSolutionForTheCVProblemInITRecruitment>Guest Voice: The Solution For The CV Problem In IT Recruitment</a>
13675 | > Originally published on 👉 <a href='https://www.fullstack.cafe\blog\the-solution-for-the-cv-problem-it-recruitment'>Guest Voice: The Solution For The CV Problem In IT Recruitment | FullStack.Cafe</a>
13676 | 
13677 | #### Q1: How do you spend your time outside work? ⭐
13678 | **Answer:**
13679 | 
13680 | 
13681 | ## [[⬆]](#toc) <a name=JavaScriptDeveloperResumeSample&Template(2019Update)>JavaScript Developer Resume Sample & Template (2019 Update)</a>
13682 | > Originally published on 👉 <a href='https://www.fullstack.cafe\blog\javascript-developer-resume-sample'>JavaScript Developer Resume Sample & Template (2019 Update) | FullStack.Cafe</a>
13683 | 
13684 | #### Q1: career test ⭐⭐⭐
13685 | **Details:**
13686 | test
13687 | 
13688 | **Answer:**
13689 | test
13690 | 
13691 | ## [[⬆]](#toc) <a name=Node.jsErrorHandling:7WaysToKillThemAll>Node.js Error Handling: 7 Ways To Kill Them All</a>
13692 | > Originally published on 👉 <a href='https://www.fullstack.cafe\blog\nodejs-error-handling-patterns-demystified-examples'>Node.js Error Handling: 7 Ways To Kill Them All | FullStack.Cafe</a>
13693 | 
13694 | #### Q1: Explain some Error Handling approaches in Node.js you know about. Which one will you use? ⭐⭐⭐⭐⭐
13695 | **Answer:**
13696 | Read Full Answer on 👉 <a href='https://www.fullstack.cafe\blog\nodejs-error-handling-patterns-demystified-examples'>FullStack.Cafe</a>
13697 | 
13698 | ## [[⬆]](#toc) <a name=TheUltimateGuidetoTransitioningtoRemoteWebDevelopment>The Ultimate Guide to Transitioning to Remote Web Development</a>
13699 | > Originally published on 👉 <a href='https://www.fullstack.cafe\blog\ultimate-guide-to-transitioning-to-remote-web-development'>The Ultimate Guide to Transitioning to Remote Web Development | FullStack.Cafe</a>
13700 | 
13701 | #### Q1: career test ⭐⭐⭐
13702 | **Details:**
13703 | test
13704 | 
13705 | **Answer:**
13706 | test
13707 | 
13708 | ## [[⬆]](#toc) <a name=Top26+ReactInterviewQuestions(2018Edition)>Top 26+ React Interview Questions (2018 Edition)</a>
13709 | > Originally published on 👉 <a href='https://www.fullstack.cafe\blog\top-26-react-redux-interview-questions-to-brush-up-2018'>Top 26+ React Interview Questions (2018 Edition) | FullStack.Cafe</a>
13710 | 
13711 | #### Q1: What is React? ⭐
13712 | **Answer:**
13713 | React is an open-source JavaScript library created by Facebook for building complex, interactive UIs in web and mobile applications. React’s core purpose is to build UI components; it is often referred to as just the “V” (View) in an “MVC” architecture. 
13714 | 
13715 | **Source:** _codementor.io_
13716 | 
13717 | #### Q2: What are the advantages of ReactJS? ⭐
13718 | **Answer:**
13719 | Below are the advantages of ReactJS:
13720 | 1. Increases the application’s performance with Virtual DOM
13721 | 2. JSX makes code is easy to read and write
13722 | 3. It renders both on client and server side
13723 | 4. Easy to integrate with other frameworks (Angular, BackboneJS) since it is only a view library
13724 | 5. Easy to write UI Test cases and integration with tools such as JEST.
13725 | 
13726 | **Source:** _github.com/sudheerj_
13727 | 
13728 | #### Q3: What are the major features of ReactJS? ⭐
13729 | **Answer:**
13730 | The major features of ReactJS are as follows,
13731 | 
13732 | - It uses **VirtualDOM** instead RealDOM considering that RealDOM manipulations are expensive.
13733 | - Supports **server-side rendering**
13734 | - Follows **Unidirectional** data flow or data binding
13735 | - Uses **reusable/composable** UI components to develop the view
13736 | 
13737 | **Source:** _https://github.com/sudheerj_
13738 | 
13739 | #### Q4: What is virtual DOM? ⭐
13740 | **Answer:**
13741 | **The virtual DOM (VDOM)** is an in-memory representation of Real DOM. The representation of a UI is kept in memory and synced with the “real” DOM. It’s a step that happens between the render function being called and the displaying of elements on the screen. This entire process is called reconciliation.
13742 | 
13743 | **Source:** _github.com/sudheerj_
13744 | 
13745 | #### Q5: What’s the difference between an "Element" and a "Component" in React? ⭐⭐
13746 | **Answer:**
13747 | Simply put, a React element describes what you want to see on the screen. Not so simply put, a React element is an object representation of some UI.
13748 | 
13749 | A React component is a function or a class which optionally accepts input and returns a React element (typically via JSX which gets transpiled to a createElement invocation).
13750 | 
13751 | **Source:** _medium.freecodecamp.org/_
13752 | 
13753 | #### Q6: What are the limitations of ReactJS? ⭐⭐
13754 | **Answer:**
13755 | Below are the list of limitations:
13756 | 
13757 | 1. React is just a view library, not a full-blown framework
13758 | 2. There is a learning curve for beginners who are new to web development.
13759 | 3. Integrating React.js into a traditional MVC framework requires some additional configuration
13760 | 4. The code complexity increases with inline templating and JSX.
13761 | 5. Too many smaller components leading to over-engineering or boilerplate
13762 | 
13763 | **Source:** _github.com/sudheerj_
13764 | 
13765 | #### Q7: What is the difference between a Presentational component and a Container component? ⭐⭐
13766 | **Answer:**
13767 | * **Presentational components** are concerned with _how things look_. They generally receive data and callbacks exclusively via props. These components rarely have their own state, but when they do it generally concerns UI state, as opposed to data state.
13768 | 
13769 | * **Container components** are more concerned with _how things work_. These components provide the data and behavior to presentational or other container components. They call Flux actions and provide these as callbacks to the presentational components. They are also often stateful as they serve as data sources. 
13770 | 
13771 | **Source:** _github.com/Pau1fitz_
13772 | 
13773 | #### Q8: How is React different from AngularJS (1.x)? ⭐⭐
13774 | **Answer:**
13775 | For example, AngularJS (1.x) approaches building an application by extending HTML markup and injecting various constructs (e.g. Directives, Controllers, Services) at runtime. As a result, AngularJS is very opinionated about the greater architecture of your application — these abstractions are certainly useful in some cases, but they come at the cost of flexibility.
13776 | 
13777 | By contrast, React focuses exclusively on the creation of components, and has few (if any) opinions about an application’s architecture. This allows a developer an incredible amount of flexibility in choosing the architecture they deem “best” — though it also places the responsibility of choosing (or building) those parts on the developer.
13778 | 
13779 | **Source:** _codementor.io_
13780 | 
13781 | #### Q9: Describe how events are handled in React. ⭐⭐
13782 | **Answer:**
13783 | In order to solve cross browser compatibility issues, your event handlers in React will be passed instances of SyntheticEvent, which is React’s cross-browser wrapper around the browser’s native event. These synthetic events have the same interface as native events you’re used to, except they work identically across all browsers.
13784 | 
13785 | What’s mildly interesting is that React doesn’t actually attach events to the child nodes themselves. React will listen to all events at the top level using a single event listener. This is good for performance and it also means that React doesn’t need to worry about keeping track of event listeners when updating the DOM.
13786 | 
13787 | **Source:** _tylermcginnis.com_
13788 | 
13789 | #### Q10: What is state in ReactJS? ⭐⭐
13790 | **Answer:**
13791 | **State** of a component is an object that holds some information that may change over the lifetime of the component. We should always try to make our state as simple as possible and minimize the number of stateful components.
13792 | 
13793 |  Let's create user component with message state,
13794 | 
13795 |  ```js
13796 |  class User extends React.Component {
13797 |     constructor(props) {
13798 |        super(props);
13799 | 
13800 |        this.state = {
13801 |           message: "Welcome to React world",
13802 |        }
13803 |     }
13804 |     render() {
13805 |        return (
13806 |           <div>
13807 |              <h1>{this.state.message}</h1>
13808 |           </div>
13809 |        );
13810 |     }
13811 |  }
13812 |  ```
13813 | 
13814 | **Source:** _https://github.com/sudheerj_
13815 | 
13816 | #### Q11: What is the difference between state and props? ⭐⭐
13817 | **Answer:**
13818 | Both **props** and **state** are plain JavaScript objects. While both of them hold information that influences the output of render, they are different in their functionality with respect to component. i.e, 
13819 | * Props get passed to the component similar to function parameters 
13820 | * state is managed within the component similar to variables declared within a function.
13821 | 
13822 | **Source:** _https://github.com/sudheerj_
13823 | 
13824 | #### Q12: What can you tell me about JSX? ⭐⭐⭐
13825 | **Answer:**
13826 | When Facebook first released React to the world, they also introduced a new dialect of JavaScript called JSX that embeds raw HTML templates inside JavaScript code. JSX code by itself cannot be read by the browser; it must be transpiled into traditional JavaScript using tools like Babel and webpack. While many developers understandably have initial knee-jerk reactions against it, JSX (in tandem with ES2015) has become the defacto method of defining React components.
13827 | 
13828 | ```js
13829 | class MyComponent extends React.Component {
13830 |   render() {
13831 |     let props = this.props;  
13832 |     return (
13833 |       <div className="my-component">
13834 |       <a href={props.url}>{props.name}</a>
13835 |       </div>
13836 |     );
13837 |   }
13838 | }
13839 | ```
13840 | 
13841 | **Source:** _codementor.io_
13842 | 
13843 | #### Q13: Why should not we update the state directly? ⭐⭐⭐
13844 | **Answer:**
13845 | If you try to update state directly then it won’t re-render the component.
13846 | 
13847 | ```js
13848 |     //Wrong
13849 |     This.state.message =”Hello world”;
13850 | ```
13851 | 
13852 | Instead use `setState()` method. It schedules an update to a component’s state object. When state changes, the component responds by re-rendering
13853 | 
13854 | ```js
13855 |     //Correct
13856 |     This.setState({message: ‘Hello World’});
13857 | ```
13858 | 
13859 | **Note:** The only place you can assign the state is constructor.
13860 | 
13861 | 
13862 | **Source:** _https://github.com/sudheerj_
13863 | 
13864 | #### Q14: What are the different phases of ReactJS component lifecycle? ⭐⭐⭐
13865 | **Answer:**
13866 | There are four different phases of React component’s lifecycle:
13867 | 1. **Initialization:** In this phase react component prepares setting up the initial state and default props.
13868 | 2. **Mounting:** The react component is ready to mount in the browser DOM. This phase covers **componentWillMount** and **componentDidMount** lifecycle methods.
13869 | 3. **Updating:** In this phase, the component get updated in two ways, sending the new props and updating the state. This phase covers **shouldComponentUpdate, componentWillUpdate and componentDidUpdate** lifecycle methods.
13870 | 4. **Unmounting:** In this last phase, the component is not needed and get unmounted from the browser DOM. This phase include **componentWillUnmount** lifecycle method.
13871 | 
13872 | <div class="text-center">
13873 | <img src="https://github.com/sudheerj/reactjs-interview-questions/raw/master/images/phases.png" class="img-fluid"/>
13874 | </div>
13875 | 
13876 | **Source:** _github.com/sudheerj_
13877 | 
13878 | #### Q15: What are error boundaries in ReactJS (16)? ⭐⭐⭐
13879 | **Answer:**
13880 | Error boundaries are React components that catch JavaScript errors anywhere in their child component tree, log those errors, and display a fallback UI instead of the component tree that crashed.
13881 | 
13882 | A class component becomes an error boundary if it defines a new lifecycle method called `componentDidCatch(error, info)`
13883 | ```js
13884 | class ErrorBoundary extends React.Component {
13885 |   constructor(props) {
13886 |     super(props);
13887 |     this.state = { hasError: false };
13888 |   }
13889 | 
13890 |   componentDidCatch(error, info) {
13891 |     // Display fallback UI
13892 |     this.setState({ hasError: true });
13893 |     // You can also log the error to an error reporting service
13894 |     logErrorToMyService(error, info);
13895 |   }
13896 | 
13897 |   render() {
13898 |     if (this.state.hasError) {
13899 |       // You can render any custom fallback UI
13900 |       return <h1>Something went wrong.</h1>;
13901 |     }
13902 |     return this.props.children;
13903 |   }
13904 | }
13905 | ```
13906 | 
13907 | After that use it as a regular component
13908 | 
13909 | ```js
13910 | <ErrorBoundary>
13911 |   <MyWidget />
13912 | </ErrorBoundary>
13913 | ```
13914 | 
13915 | **Source:** _github.com/sudheerj_
13916 | 
13917 | #### Q16: Why ReactJS uses className over class attribute? ⭐⭐⭐
13918 | **Answer:**
13919 | **class** is a keyword in javascript and JSX is an extension of javascript. That's the principal reason why React uses `className` instead of class. 
13920 | 
13921 | ```js
13922 | render() {
13923 |   return <span className="menu navigation-menu">Menu</span>
13924 | }
13925 | ```
13926 | 
13927 | **Source:** _github.com/sudheerj_
13928 | 
13929 | #### Q17: What is the difference between a controlled component and an uncontrolled component? ⭐⭐⭐⭐
13930 | **Answer:**
13931 | Read Full Answer on 👉 <a href='https://www.fullstack.cafe\blog\top-26-react-redux-interview-questions-to-brush-up-2018'>FullStack.Cafe</a>
13932 | 
13933 | #### Q18: What is wrong with this code? ⭐⭐⭐⭐
13934 | **Answer:**
13935 | Read Full Answer on 👉 <a href='https://www.fullstack.cafe\blog\top-26-react-redux-interview-questions-to-brush-up-2018'>FullStack.Cafe</a>
13936 | 
13937 | #### Q19: Why would you use forceUpdate in a React component? ⭐⭐⭐⭐
13938 | **Answer:**
13939 | Read Full Answer on 👉 <a href='https://www.fullstack.cafe\blog\top-26-react-redux-interview-questions-to-brush-up-2018'>FullStack.Cafe</a>
13940 | 
13941 | #### Q20: Describe Flux vs MVC? ⭐⭐⭐⭐
13942 | **Answer:**
13943 | Read Full Answer on 👉 <a href='https://www.fullstack.cafe\blog\top-26-react-redux-interview-questions-to-brush-up-2018'>FullStack.Cafe</a>
13944 | 
13945 | #### Q21: Explain some difference between Flux and AngularJS (1.x) approach ⭐⭐⭐⭐⭐
13946 | **Answer:**
13947 | Read Full Answer on 👉 <a href='https://www.fullstack.cafe\blog\top-26-react-redux-interview-questions-to-brush-up-2018'>FullStack.Cafe</a>
13948 | 
13949 | #### Q22: What is a pure function? ⭐⭐⭐⭐⭐
13950 | **Answer:**
13951 | Read Full Answer on 👉 <a href='https://www.fullstack.cafe\blog\top-26-react-redux-interview-questions-to-brush-up-2018'>FullStack.Cafe</a>
13952 | 
13953 | #### Q23: What is Redux? ⭐
13954 | **Answer:**
13955 | **Redux** is a predictable state container for JavaScript apps based on the Flux design pattern. Redux can be used together with ReactJS, or with any other view library. It is tiny (about 2kB) and has no dependencies.
13956 | 
13957 | **Source:** _github.com/sudheerj_
13958 | 
13959 | #### Q24: What is Flux? ⭐
13960 | **Answer:**
13961 | **Flux** is an application design paradigm used as a replacement for the more traditional mvc pattern. It is not a framework or a library but a new kind of architecture that complements React and the concept of Unidirectional Data Flow. Facebook used this pattern internally when working with React The workflow between dispatcher, stores and views components with distinct inputs and outputs as follows:
13962 | 
13963 | <div class="text-center"/>
13964 | <img src="https://github.com/sudheerj/reactjs-interview-questions/raw/master/images/flux.png" class="img-fluid"/>
13965 | </div>
13966 | 
13967 | 
13968 | **Source:** _github.com/sudheerj_
13969 | 
13970 | #### Q25: How to access redux store outside a react component? ⭐⭐⭐
13971 | **Answer:**
13972 | Yes.You just need to export the store from the module where it created with `createStore`. Also, it shouldn't pollute the global window object
13973 | ```js
13974 | store = createStore(myReducer);
13975 | export default store;
13976 | ```
13977 | 
13978 | **Source:** _github.com/sudheerj_
13979 | 
13980 | #### Q26: What are the downsides of Redux over Flux? ⭐⭐⭐
13981 | **Answer:**
13982 | Instead of saying downsides we can say that there are few compromises of using Redux over Flux. Those are as follows:
13983 | 1. **You will need to learn avoiding mutations:**
13984 | Flux is un-opinionated about mutating data, but Redux doesn't like mutations and many packages complementary to Redux assume you never mutate the state. You can enforce this with dev-only packages like redux-immutable-state-invariant, Immutable.js, or your team to write non-mutative code.
13985 | 2. **You're going to have to carefully pick your packages:**
13986 | While Flux explicitly doesn't try to solve problems such as undo/redo, persistence, or forms, Redux has extension points such as middleware and store enhancers, and it has spawned a young but rich ecosystem. This means most packages are new ideas and haven't received the critical mass of usage yet
13987 | 3. **There is no nice Flow integration yet:**
13988 | Flux currently lets you do very impressive static type checks which Redux doesn't support yet.
13989 | 
13990 | **Source:** _github.com/sudheerj_
13991 | 
13992 | ## [[⬆]](#toc) <a name=Top60+MEANStackDeveloperInterviewQuestionsAndAnswers(2019Edition)>Top 60+ MEAN Stack Developer Interview Questions And Answers (2019 Edition)</a>
13993 | > Originally published on 👉 <a href='https://www.fullstack.cafe\blog\top-60-mean-stack-interview-questions-and-answers'>Top 60+ MEAN Stack Developer Interview Questions And Answers (2019 Edition) | FullStack.Cafe</a>
13994 | 
13995 | #### Q1: What is Routing Guard in Angular? ⭐
13996 | **Answer:**
13997 | Angular’s route guards are interfaces which can tell the router whether or not it should allow navigation to a requested route. They make this decision by looking for a true or false return value from a class which implements the given guard interface.
13998 | 
13999 | **Source:** _medium.com_
14000 | 
14001 | #### Q2: What is a service, and when will you use it? ⭐⭐
14002 | **Answer:**
14003 | *Angular services* are singleton objects which get instantiated only once during the lifetime of an application. They contain methods that maintain data throughout the life of an application, i.e. data does not get refreshed and is available all the time. The main objective of a service is to organize and share business logic, models, or data and functions with different components of an Angular application.
14004 | 
14005 | The *separation of concerns* is the main reason why Angular services came into existence. An Angular service is a stateless object and provides some very useful functions. 
14006 | 
14007 | **Source:** _dzone.com_
14008 | 
14009 | #### Q3: How to bundle an Angular app for production? ⭐⭐⭐
14010 | **Answer:**
14011 | **OneTime Setup**
14012 | 
14013 | *   `npm install -g @angular/cli`
14014 | *   `ng new projectFolder` creates a new application
14015 | 
14016 | **Bundling Step**
14017 | 
14018 | *   `ng build --prod` (run in command line when directory is `projectFolder`)
14019 | *   flag `prod` _bundle for production
14020 | 
14021 | _bundles are generated by default to_ **_projectFolder/dist/_**
14022 | 
14023 | **Deployment**
14024 | 
14025 | You can get a preview of your application using the `ng serve --prod` command that starts a local HTTP server such that the application with production files is accessible using [http://localhost:4200](http://localhost:4200).
14026 | 
14027 | For a production usage, you have to deploy all the files from the `dist` folder in the HTTP server of your choice.
14028 | 
14029 | **Source:** _medium.com_
14030 | 
14031 | #### Q4: What's new in Angular 6 and why shall we upgrade to it? ⭐⭐⭐
14032 | **Answer:**
14033 | * **Angular Elements** - Angular Elements is a project that lets you wrap your Angular components as Web Components and embed them in a non-Angular application. 
14034 | * **New Rendering Engine: Ivy** -  increases in speed and decreases in application size.
14035 | * **Tree-shakeable providers** - a new, recommended, way to register a provider, directly inside the @Injectable() decorator, using the new `providedIn` attribute
14036 | * **RxJS 6** - Angular 6 now uses RxJS 6 internally, and requires you to update your application also. RxJS released a library called rxjs-compat, that allows you to bump RxJS to version 6.0 even if you, or one of the libraries you’re using, is still using one of the “old” syntaxes.
14037 | * **ElementRef`<T>`** - in Angular 5.0 or older, is that the said ElementRef had its nativeElement property typed as any. In Angular 6.0, you can now type ElementRef more strictly. 
14038 | * **Animations** - The polyfill web-animations-js is not necessary anymore for animations in Angular 6.0, except if you are using the AnimationBuilder.
14039 | * **i18n** - possibility to have “runtime i18n”, without having to build the application once per locale. 
14040 | 
14041 | 
14042 | **Source:** _ninja-squad.com_
14043 | 
14044 | #### Q5: What is AOT? ⭐⭐⭐
14045 | **Answer:**
14046 | The Angular Ahead-of-Time compiler pre-compiles application components and their templates during the build process.
14047 | Apps compiled with AOT launch faster for several reasons. 
14048 | * Application components execute immediately, without client-side compilation. 
14049 | * Templates are embedded as code within their components so there is no client-side request for template files. 
14050 | * You don't download the Angular compiler, which is pretty big on its own. 
14051 | * The compiler discards unused Angular directives that a tree-shaking tool can then exclude.
14052 | 
14053 | **Source:** _stackoverflow.com_
14054 | 
14055 | #### Q6: What is Redux and how does it relate to an Angular app? ⭐⭐⭐
14056 | **Answer:**
14057 | **Redux** is a way to manage application state and improve maintainability of asynchronicity in your application by providing a single source of truth for the application state, and a unidirectional flow of data change in the application. `ngrx/store` is one implementation of Redux principles.
14058 | 
14059 | **Source:** _github.com/WebPredict_
14060 | 
14061 | #### Q7: How to set headers for every request in Angular? ⭐⭐⭐⭐
14062 | **Answer:**
14063 | Read Full Answer on 👉 <a href='https://www.fullstack.cafe\blog\top-60-mean-stack-interview-questions-and-answers'>FullStack.Cafe</a>
14064 | 
14065 | #### Q8: Just-in-Time (JiT) vs Ahead-of-Time (AoT) compilation. Explain the difference. ⭐⭐⭐⭐⭐
14066 | **Answer:**
14067 | Read Full Answer on 👉 <a href='https://www.fullstack.cafe\blog\top-60-mean-stack-interview-questions-and-answers'>FullStack.Cafe</a>
14068 | 
14069 | #### Q9: Do you know how you can run angularJS and angular side by side? ⭐⭐⭐⭐⭐
14070 | **Answer:**
14071 | Read Full Answer on 👉 <a href='https://www.fullstack.cafe\blog\top-60-mean-stack-interview-questions-and-answers'>FullStack.Cafe</a>
14072 | 
14073 | #### Q10: What is a Grid System in CSS? ⭐⭐⭐
14074 | **Answer:**
14075 | A grid system is a structure that allows for content to be stacked both vertically and horizontally in a consistent and easily manageable fashion. Grid systems include two key components: rows and columns.
14076 | 
14077 | Some Grid Systems:
14078 | * Simple Grid
14079 | * Pure
14080 | * Flexbox Grid
14081 | * Bootstrap
14082 | * Foundation
14083 | 
14084 | **Source:** _sitepoint.com_
14085 | 
14086 | #### Q11: How is responsive design different from adaptive design? ⭐⭐⭐
14087 | **Answer:**
14088 | Both *responsive* and *adaptive* design attempt to optimize the user experience across different devices, adjusting for different viewport sizes, resolutions, usage contexts, control mechanisms, and so on.
14089 | 
14090 | **Responsive design** works on the principle of flexibility — a single fluid website that can look good on any device. Responsive websites use *media queries*, *flexible grids*, and *responsive images* to create a user experience that flexes and changes based on a multitude of factors. Like a single ball growing or shrinking to fit through several different hoops.
14091 | 
14092 | **Adaptive design** is more like the modern definition of progressive enhancement. Instead of one flexible design, adaptive design detects the device and other features, and then provides the appropriate feature and layout based on a *predefined set of viewport sizes* and other characteristics. The site detects the type of device used, and delivers the pre-set layout for that device. Instead of a single ball going through several different-sized hoops, you’d have several different balls to use depending on the hoop size.
14093 | 
14094 | **Source:** _codeburst.io_
14095 | 
14096 | #### Q12: Explain the basic rules of CSS Specificity ⭐⭐⭐⭐
14097 | **Answer:**
14098 | Read Full Answer on 👉 <a href='https://www.fullstack.cafe\blog\top-60-mean-stack-interview-questions-and-answers'>FullStack.Cafe</a>
14099 | 
14100 | #### Q13: What is the difference between Linear Search and Binary Search? ⭐⭐
14101 | **Answer:**
14102 | * A **linear search** looks down a list, one item at a time, without jumping. In complexity terms this is an `O(n)` search - the time taken to search the list gets bigger at the same rate as the list does.
14103 | 
14104 | * A **binary search** is when you start with the middle of a sorted list, and see whether that's greater than or less than the value you're looking for, which determines whether the value is in the first or second half of the list. Jump to the half way through the sublist, and compare again etc. In complexity terms this is an `O(log n)` search - the number of search operations grows more slowly than the list does, because you're halving the "search space" with each operation.
14105 | 
14106 | Comparing the two:
14107 | 
14108 | - Binary search requires the input data to be sorted; linear search doesn't
14109 | - Binary search requires an *ordering* comparison; linear search only requires equality comparisons
14110 | - Binary search has complexity `O(log n)`; linear search has complexity O(n)
14111 | - Binary search requires random access to the data; linear search only requires sequential access (this can be very important - it means a linear search can *stream* data of arbitrary size)
14112 | 
14113 | **Source:** _wikipedia.org_
14114 | 
14115 | #### Q14: What is Dependency Injection? ⭐⭐
14116 | **Answer:**
14117 | *Dependency injection* makes it easy to create loosely coupled components, which typically means that components consume functionality defined by interfaces without having any first-hand knowledge of which implementation classes are being used.
14118 | 
14119 | *Dependency injection* makes it easier to change the behavior of an application by changing the components that implement the interfaces that define application features. It also results in components that are easier to isolate for unit testing.
14120 | 
14121 | **Source:** _Pro ASP.NET Core MVC 2_
14122 | 
14123 | #### Q15: What is Inversion of Control? ⭐⭐
14124 | **Answer:**
14125 | 
14126 | *Inversion of control* is a broad term but for a software developer it's most commonly described as a pattern used for decoupling components and layers in the system. 
14127 | 
14128 | For example, say your application has a text editor component and you want to provide spell checking. Your standard code would look something like this:
14129 | ```js
14130 | public class TextEditor {
14131 | 
14132 |     private SpellChecker checker;
14133 | 
14134 |     public TextEditor() {
14135 |         this.checker = new SpellChecker();
14136 |     }
14137 | }
14138 | ```
14139 | What we've done here creates a dependency between the TextEditor and the SpellChecker. In an IoC scenario we would instead do something like this:
14140 | ```js
14141 | public class TextEditor {
14142 | 
14143 |     private IocSpellChecker checker;
14144 | 
14145 |     public TextEditor(IocSpellChecker checker) {
14146 |         this.checker = checker;
14147 |     }
14148 | }
14149 | ```
14150 | 
14151 | You have *inverted control* by handing the responsibility of instantiating the spell checker from the TextEditor class to the caller.
14152 | 
14153 | ```js
14154 | SpellChecker sc = new SpellChecker; // dependency
14155 | TextEditor textEditor = new TextEditor(sc);
14156 | ```
14157 | 
14158 | 
14159 | **Source:** _stackoverflow.com_
14160 | 
14161 | #### Q16: What is Prototype pattern? ⭐⭐⭐
14162 | **Answer:**
14163 | *Prototype pattern* refers to creating duplicate object while keeping performance in mind. This pattern involves implementing a prototype interface which tells to create a clone of the current object.
14164 | 
14165 | <img src="https://cppcodetips.files.wordpress.com/2014/11/prototypepattern.png?w=640&h=388f" class="image-fluid center"/>
14166 | 
14167 | *The Prototype pattern* is used when creation of object directly is costly. For example, an object is to be created after a costly database operation. We can cache the object, returns its clone on next request and update the database as and when needed thus reducing database calls.
14168 | 
14169 | **Source:** _tutorialspoint.com_
14170 | 
14171 | #### Q17: Which are the top DevOps tools? Which tools have you worked on? ⭐⭐
14172 | **Answer:**
14173 | The most popular DevOps tools are:
14174 | 
14175 | *   **Git**: Version Control System tool
14176 | *   **Jenkins**: Continuous Integration tool
14177 | *   **Selenium**: Continuous Testing tool
14178 | *   **Puppet, Chef, Ansible**: Configuration Management and Deployment tools
14179 | *   **Nagios**: Continuous Monitoring tool
14180 | *   **Docker**: Containerization tool
14181 | 
14182 | **Source:** _edureka.co_
14183 | 
14184 | #### Q18: What does Containerization mean? ⭐⭐
14185 | **Answer:**
14186 | *Containerisation* is a type of *virtualization* strategy that emerged as an alternative to traditional hypervisor-based virtualization. 
14187 | 
14188 | In containerization, the operating system is shared by the different containers rather than cloned for each virtual machine. For example Docker provides a container virtualization platform that serves as a good alternative to hypervisor-based arrangements.
14189 | 
14190 | **Source:** _linoxide.com_
14191 | 
14192 | #### Q19: What's the difference between a blue/green deployment and a rolling deployment? ⭐⭐⭐
14193 | **Answer:**
14194 | * In **Blue Green Deployment**, you have TWO complete environments.
14195 | One is Blue environment which is running and the Green environment to which you want to upgrade. Once you swap the environment from blue to green, the traffic is directed to your new green environment. You can delete or save your old blue environment for backup until the green environment is stable.
14196 | 
14197 | * In **Rolling Deployment**, you have only ONE complete environment. The code is deployed in the subset of instances of the same environment and moves to another subset after completion.
14198 | 
14199 | **Source:** _stackoverflow.com_
14200 | 
14201 | #### Q20: How does the Centralized Workflow work? ⭐⭐
14202 | **Answer:**
14203 | The **Centralized Workflow** uses a central repository to serve as the single point-of-entry for all changes to the project. The default development branch is called master and all changes are committed into this branch.
14204 | 
14205 | Developers start by cloning the central repository. In their own local copies of the project, they edit files and commit changes. These new commits are stored locally.
14206 | 
14207 | To publish changes to the official project, developers *push* their local master branch to the central repository. Before the developer can publish their feature, they need to *fetch* the updated central commits and rebase their changes on top of them. 
14208 | 
14209 | Compared to other workflows, the Centralized Workflow has no defined pull request or forking patterns. 
14210 | 
14211 | **Source:** _atlassian.com_
14212 | 
14213 | #### Q21: Could you explain the Gitflow workflow? ⭐⭐⭐
14214 | **Answer:**
14215 | Gitflow workflow employs two parallel *long-running* branches to record the history of the project, `master` and `develop`:
14216 | * **Master** -  is always ready to be released on LIVE, with everything fully tested and approved (production-ready).
14217 |  * **Hotfix** - Maintenance or “hotfix” branches are used to quickly patch production releases. Hotfix branches are a lot like release branches and feature branches except they're based on `master` instead of `develop`.
14218 | 
14219 | 
14220 | * **Develop** - is the branch to which all feature branches are merged and where all tests are performed. Only when everything’s been thoroughly checked and fixed it can be merged to the `master`.
14221 |  * **Feature** - Each new feature should reside in its own branch, which can be pushed to the `develop` branch as their parent one.
14222 | 
14223 | <div class="text-center">
14224 | <img src="https://res.cloudinary.com/practicaldev/image/fetch/s--pLQxGakq--/c_limit%2Cf_auto%2Cfl_progressive%2Cq_auto%2Cw_880/https://wac-cdn.atlassian.com/dam/jcr:61ccc620-5249-4338-be66-94d563f2843c/05%2520%282%29.svg%3FcdnVersion%3Dji" class="img-fluid" style="max-width: 500px;"/>
14225 | </div>
14226 | 
14227 | 
14228 | **Source:** _atlassian.com_
14229 | 
14230 | #### Q22: Explain the main difference between REST and GraphQL ⭐⭐⭐
14231 | **Answer:**
14232 | The main and most important difference between REST and GraphQL is that *GraphQL is not dealing with dedicated resources, instead everything is regarded as a graph and therefore is connected and can be queried to app exact needs*.
14233 | 
14234 | **Source:** _medium.com/codingthesmartway-com-blog_
14235 | 
14236 | #### Q23: Are there any disadvantages to GraphQL? ⭐⭐⭐⭐
14237 | **Answer:**
14238 | Read Full Answer on 👉 <a href='https://www.fullstack.cafe\blog\top-60-mean-stack-interview-questions-and-answers'>FullStack.Cafe</a>
14239 | 
14240 | #### Q24: Describe the difference between a 'cookie', 'sessionStorage' and 'localStorage'. ⭐⭐⭐
14241 | **Answer:**
14242 | All the above-mentioned technologies are key-value storage mechanisms on the client side. They are only able to store values as strings.
14243 | 
14244 | |                                        | `cookie`                                                 | `localStorage` | `sessionStorage` |
14245 | | -------------------------------------- | -------------------------------------------------------- | -------------- | ---------------- |
14246 | | Initiator                              | Client or server. Server can use `Set-Cookie` header     | Client         | Client           |
14247 | | Expiry                                 | Manually set                                             | Forever        | On tab close     |
14248 | | Persistent across browser sessions     | Depends on whether expiration is set                     | Yes            | No               |
14249 | | Sent to server with every HTTP request | Cookies are automatically being sent via `Cookie` header | No             | No               |
14250 | | Capacity (per domain)                  | 4kb                                                      | 5MB            | 5MB              |
14251 | | Accessibility                          | Any window                                               | Any window     | Same tab         |
14252 | 
14253 | **Source:** _developer.mozilla.org_
14254 | 
14255 | #### Q25: What are the building blocks of HTML5? ⭐⭐⭐⭐
14256 | **Answer:**
14257 | Read Full Answer on 👉 <a href='https://www.fullstack.cafe\blog\top-60-mean-stack-interview-questions-and-answers'>FullStack.Cafe</a>
14258 | 
14259 | #### Q26: What is Scope in JavaScript? ⭐
14260 | **Answer:**
14261 | In JavaScript, each function gets its own *scope*. Scope is basically a collection of variables as well as the rules for how those variables are accessed by name. Only code inside that function can access that function's scoped variables.
14262 | 
14263 | A variable name has to be unique within the same scope. A scope can be nested inside another scope. If one scope is nested inside another, code inside the innermost scope can access variables from either scope.
14264 | 
14265 | #### Q27: How would you use a closure to create a private counter? ⭐⭐
14266 | **Answer:**
14267 | You can create a function within an outer function (a closure) that allows you to update a private variable but the variable wouldn't be accessible from outside the function without the use of a helper function.
14268 | 
14269 | ```js
14270 | function counter() {
14271 |   var _counter = 0;
14272 |   // return an object with several functions that allow you
14273 |   // to modify the private _counter variable
14274 |   return {
14275 |     add: function(increment) { _counter += increment; },
14276 |     retrieve: function() { return 'The counter is currently at: ' + _counter; }
14277 |   }
14278 | }
14279 | 
14280 | // error if we try to access the private variable like below
14281 | // _counter;
14282 | 
14283 | // usage of our counter function
14284 | var c = counter();
14285 | c.add(5); 
14286 | c.add(9); 
14287 | 
14288 | // now we can access the private variable in the following way
14289 | c.retrieve(); // => The counter is currently at: 14
14290 | ```
14291 | 
14292 | **Source:** _coderbyte.com_
14293 | 
14294 | #### Q28: Could you explain the difference between ES5 and ES6 ⭐⭐⭐
14295 | **Answer:**
14296 | * **ECMAScript 5 (ES5)**: The 5th edition of ECMAScript, standardized in 2009. This standard has been implemented fairly completely in all modern browsers
14297 | 
14298 | * **ECMAScript 6 (ES6)/ ECMAScript 2015 (ES2015)**: The 6th edition of ECMAScript, standardized in 2015. This standard has been partially implemented in most modern browsers.
14299 | 
14300 | Here are some key differences between ES5 and ES6:
14301 | * **Arrow functions** & **string interpolation**:<br/>
14302 | Consider:
14303 | ```js
14304 | const greetings = (name) => {
14305 |       return `hello ${name}`;
14306 | }
14307 | ```
14308 | and even:
14309 | ```js
14310 | const greetings = name => `hello ${name}`;
14311 | ```
14312 | * **Const**. <br>
14313 | Const works like a constant in other languages in many ways but there are some caveats. Const stands for ‘constant reference’ to a value. So with const, you can actually mutate the properties of an object being referenced by the variable. You just can’t change the reference itself.
14314 | ```js
14315 | const NAMES = [];
14316 | NAMES.push("Jim");
14317 | console.log(NAMES.length === 1); // true
14318 | NAMES = ["Steve", "John"]; // error
14319 | ```
14320 | * **Block-scoped variables**.<br>
14321 | The new ES6 keyword `let` allows developers to scope variables at the block level.
14322 | `Let` doesn’t hoist in the same way `var` does.
14323 | * **Default parameter values**
14324 | Default parameters allow us to initialize functions with default values. A default is used when an argument is either omitted or undefined — meaning null is a valid value.
14325 | ```js
14326 | // Basic syntax
14327 | function multiply (a, b = 2) {
14328 |      return a * b;
14329 | }
14330 | multiply(5); // 10
14331 | ```
14332 | * ** Class Definition and Inheritance**<br>
14333 | ES6 introduces language support for classes (`class` keyword), constructors (`constructor` keyword), and the `extend` keyword for inheritance.
14334 | 
14335 | * **for-of operator**<br>
14336 | The for...of statement creates a loop iterating over iterable objects.
14337 | * **Spread Operator**
14338 | For objects merging
14339 | ```js
14340 | const obj1 = { a: 1, b: 2 }
14341 | const obj2 = { a: 2, c: 3, d: 4}
14342 | const obj3 = {...obj1, ...obj2}
14343 | ```
14344 | * **Promises**<br>
14345 | Promises provide a mechanism to handle the results and errors from asynchronous operations.  You can accomplish the same thing with callbacks, but promises provide improved readability via method chaining and succinct error handling. 
14346 | ```js
14347 | const isGreater = (a, b) => {
14348 |   return new Promise ((resolve, reject) => {
14349 |     if(a > b) {
14350 |       resolve(true)
14351 |     } else {
14352 |       reject(false)
14353 |     }
14354 |     })
14355 | }
14356 | isGreater(1, 2)
14357 |   .then(result => {
14358 |     console.log('greater')
14359 |   })
14360 |  .catch(result => {
14361 |     console.log('smaller')
14362 |  })
14363 | ```
14364 | * **Modules exporting & importing**
14365 | Consider module exporting:
14366 | ```js
14367 | const myModule = { x: 1, y: () => { console.log('This is ES5') }}
14368 | export default myModule;
14369 | ```
14370 | and importing:
14371 | ```js
14372 | import myModule from './myModule';
14373 | ```
14374 | 
14375 | 
14376 | #### Q29: Given two strings, return true if they are anagrams of one another ⭐⭐⭐
14377 | **Details:**
14378 | For example: `Mary` is an anagram of `Army`
14379 | 
14380 | **Answer:**
14381 | ```js
14382 | var firstWord = "Mary";
14383 | var secondWord = "Army";
14384 | 
14385 | isAnagram(firstWord, secondWord); // true
14386 | 
14387 | function isAnagram(first, second) {
14388 |   // For case insensitivity, change both words to lowercase.
14389 |   var a = first.toLowerCase();
14390 |   var b = second.toLowerCase();
14391 | 
14392 |   // Sort the strings, and join the resulting array to a string. Compare the results
14393 |   a = a.split("").sort().join("");
14394 |   b = b.split("").sort().join("");
14395 | 
14396 |   return a === b;
14397 | }
14398 | ```
14399 | 
14400 | **Source:** _https://github.com/kennymkchan_
14401 | 
14402 | #### Q30: How would you create a private variable in JavaScript? ⭐⭐⭐⭐
14403 | **Answer:**
14404 | Read Full Answer on 👉 <a href='https://www.fullstack.cafe\blog\top-60-mean-stack-interview-questions-and-answers'>FullStack.Cafe</a>
14405 | 
14406 | #### Q31: Compare SQL databases and MongoDB at a high level. ⭐⭐
14407 | **Answer:**
14408 | SQL databases store data in form of tables, rows, columns and records. This data is stored in a pre-defined data model which is not very much flexible for today's real-world highly growing applications. MongoDB in contrast uses a flexible structure which can be easily modified and extended.
14409 | 
14410 | **Source:** _tutorialspoint.com_
14411 | 
14412 | #### Q32: What is BSON in MongoDB? ⭐⭐
14413 | **Answer:**
14414 | **BSON** is a binary serialization format used to store documents and make remote procedure calls in MongoDB. BSON extends the JSON model to provide additional data types, ordered fields, and to be efficient for encoding and decoding within different languages. 
14415 | 
14416 | 
14417 | **Source:** _mongodb.com_
14418 | 
14419 | #### Q33: What are Indexes in MongoDB? ⭐⭐
14420 | **Answer:**
14421 | Indexes support the efficient execution of queries in MongoDB. Without indexes, MongoDB must perform a collection scan, i.e. scan every document in a collection, to select those documents that match the query statement. If an appropriate index exists for a query, MongoDB can use the index to limit the number of documents it must inspect.
14422 | 
14423 | **Source:** _tutorialspoint.com_
14424 | 
14425 | #### Q34: What does MongoDB not being ACID compliant really mean? ⭐⭐⭐
14426 | **Answer:**
14427 | It's actually not correct that MongoDB is not ACID-compliant. On the contrary, MongoDB is ACID-compilant at the document level.
14428 | 
14429 | Any update to a single document is
14430 | 
14431 | * **Atomic**: it either fully completes or it does not
14432 | * **Consistent**: no reader will see a "partially applied" update
14433 | * **Isolated**: again, no reader will see a "dirty" read
14434 | * **Durable**: (with the appropriate write concern)
14435 | 
14436 | What MongoDB doesn't have is *transactions* - that is, multiple-document updates that can be rolled back and are ACID-compliant.
14437 | 
14438 | Multi-document transactions, scheduled for MongoDB 4.0 in Summer 2018*, will feel just like the transactions developers are familiar with from relational databases – multi-statement, similar syntax, and easy to add to any application.
14439 | 
14440 | **Source:** _stackoverflow.com_
14441 | 
14442 | #### Q35: What is Aggregation in MongoDB? ⭐⭐⭐
14443 | **Answer:**
14444 | *Aggregations* operations process data records and return computed results. Aggregation operations group values from multiple documents together, and can perform a variety of operations on the grouped data to return a single result. MongoDB provides three ways to perform aggregation: 
14445 | * the aggregation pipeline,
14446 | * the map-reduce function, 
14447 | * and single purpose aggregation methods and commands.
14448 | 
14449 | **Source:** _tutorialspoint.com_
14450 | 
14451 | #### Q36: How to query MongoDB with “like”? ⭐⭐⭐
14452 | **Answer:**
14453 | I want to query something as SQL's like query:
14454 | ```js
14455 | select * 
14456 | from users 
14457 | where name like '%m%'
14458 | ```
14459 | How to do the same in MongoDB?
14460 | 
14461 | **Answer**
14462 | 
14463 | ```js
14464 | db.users.find({"name": /.*m.*/})
14465 | // or
14466 | db.users.find({"name": /m/})
14467 | ```
14468 | You're looking for something that contains "m" somewhere (SQL's `'%'` operator is equivalent to Regexp's `'.*'`), not something that has "m" anchored to the beginning of the string.
14469 | 
14470 | 
14471 | **Source:** _stackoverflow.com_
14472 | 
14473 | #### Q37: How can I combine data from multiple collections into one collection? ⭐⭐⭐
14474 | **Answer:**
14475 | MongoDB 3.2 allows one to combine data from multiple collections into one through the `$lookup` aggregation stage. 
14476 | 
14477 | ```js
14478 | db.books.aggregate([{
14479 |     $lookup: {
14480 |             from: "books_selling_data",
14481 |             localField: "isbn",
14482 |             foreignField: "isbn",
14483 |             as: "copies_sold"
14484 |         }
14485 | }])
14486 | ```
14487 | 
14488 | **Source:** _stackoverflow.com_
14489 | 
14490 | #### Q38: How do I perform the SQL JOIN equivalent in MongoDB? ⭐⭐⭐
14491 | **Answer:**
14492 | Mongo is not a relational database, and the devs are being careful to recommend specific use cases for $lookup, but at least as of 3.2 doing join is now possible with MongoDB. The new $lookup operator added to the aggregation pipeline is essentially identical to a left outer join:
14493 | 
14494 | ```js
14495 | {
14496 |    $lookup:
14497 |      {
14498 |        from: <collection to join>,
14499 |        localField: <field from the input documents>,
14500 |        foreignField: <field from the documents of the "from" collection>,
14501 |        as: <output array field>
14502 |      }
14503 | }
14504 | ```
14505 | 
14506 | **Source:** _stackoverflow.com_
14507 | 
14508 | #### Q39: How to query MongoDB with %like%? ⭐⭐⭐
14509 | **Details:**
14510 | I want to query something as SQL's like query:
14511 | 
14512 | ```sql
14513 | select * 
14514 | from users 
14515 | where name like '%m%'
14516 | ```
14517 | How to do the same in MongoDB?
14518 | 
14519 | **Answer:**
14520 | ```js
14521 | db.users.find({name: /a/})  //like '%a%'
14522 | db.users.find({name: /^pa/}) //like 'pa%'
14523 | db.users.find({name: /ro$/}) //like '%ro'
14524 | ```
14525 | Or using Mongoose:
14526 | ```js
14527 | db.users.find({'name': {'$regex': 'sometext'}})
14528 | ```
14529 | 
14530 | **Source:** _stackoverflow.com_
14531 | 
14532 | #### Q40: What are the benefits of using Node.js? ⭐⭐
14533 | **Answer:**
14534 | Following are main benefits of using Node.js
14535 | 
14536 | *   **Aynchronous and Event Driven** - All APIs of Node.js library are aynchronous that is non-blocking. It essentially means a Node.js based server never waits for a API to return data. Server moves to next API after calling it and a notification mechanism of Events of Node.js helps server to get response from the previous API call.
14537 | *   **Very Fast** - Being built on Google Chrome's V8 JavaScript Engine, Node.js library is very fast in code execution.
14538 | *   **Single Threaded but highly Scalable** - Node.js uses a single threaded model with event looping. Event mechanism helps server to respond in a non-bloking ways and makes server highly scalable as opposed to traditional servers which create limited threads to handle requests. Node.js uses a single threaded program and same program can services much larger number of requests than traditional server like Apache HTTP Server.
14539 | *   **No Buffering** \- Node.js applications never buffer any data. These applications simply output the data in chunks.
14540 | 
14541 | **Source:** _tutorialspoint.com_
14542 | 
14543 | #### Q41: What is a blocking code? ⭐⭐⭐
14544 | **Answer:**
14545 | If application has to wait for some I/O operation in order to complete its execution any further then the code responsible for waiting is known as blocking code.
14546 | 
14547 | **Source:** _tutorialspoint.com_
14548 | 
14549 | #### Q42: How can you avoid callback hells? ⭐⭐⭐
14550 | **Answer:**
14551 | To do so you have more options:
14552 | 
14553 | *   **modularization**: break callbacks into independent functions
14554 | *   use _Promises_
14555 | *   use `yield` with _Generators_ and/or _Promises_
14556 | 
14557 | **Source:** _tutorialspoint.com_
14558 | 
14559 | #### Q43: What's the event loop? ⭐⭐⭐
14560 | **Answer:**
14561 | **The event loop** is what allows Node.js to perform non-blocking I/O operations — despite the fact that JavaScript is single-threaded — by offloading operations to the system kernel whenever possible.
14562 | 
14563 | <div class="text-center">
14564 | <img src="https://i.stack.imgur.com/Lbs9z.png" class="img-fluid">
14565 | </div>
14566 | 
14567 | Every I/O requires a callback - once they are done they are pushed onto the event loop for execution. Since most modern kernels are multi-threaded, they can handle multiple operations executing in the background. When one of these operations completes, the kernel tells Node.js so that the appropriate callback may be added to the poll queue to eventually be executed.
14568 | 
14569 | **Source:** _blog.risingstack.com_
14570 | 
14571 | #### Q44: How does Node.js handle child threads? ⭐⭐⭐
14572 | **Answer:**
14573 | Node.js, in its essence, is a single thread process. It does not expose child threads and thread management methods to the developer. Technically, Node.js does spawn child threads for certain tasks such as asynchronous I/O, but these run behind the scenes and do not execute any application JavaScript code, nor block the main event loop.
14574 | 
14575 | If threading support is desired in a Node.js application, there are tools available to enable it, such as the ChildProcess module.
14576 | 
14577 | **Source:** _lazyquestion.com_
14578 | 
14579 | #### Q45: When should I use EventEmitter? ⭐⭐⭐
14580 | **Answer:**
14581 | Whenever it makes sense for code to *subscribe* to something rather than get a callback from something. The typical use case would be that there's multiple blocks of code in your application that may need to do something when an event happens.
14582 | 
14583 | **Source:** _stackoverflow.com/_
14584 | 
14585 | #### Q46: Explain usage of NODE_ENV ⭐⭐⭐⭐
14586 | **Answer:**
14587 | Read Full Answer on 👉 <a href='https://www.fullstack.cafe\blog\top-60-mean-stack-interview-questions-and-answers'>FullStack.Cafe</a>
14588 | 
14589 | #### Q47: How would you scale Node application? ⭐⭐⭐⭐⭐
14590 | **Answer:**
14591 | Read Full Answer on 👉 <a href='https://www.fullstack.cafe\blog\top-60-mean-stack-interview-questions-and-answers'>FullStack.Cafe</a>
14592 | 
14593 | #### Q48: Explain some Error Handling approaches in Node.js you know about. Which one will you use? ⭐⭐⭐⭐⭐
14594 | **Answer:**
14595 | Read Full Answer on 👉 <a href='https://www.fullstack.cafe\blog\top-60-mean-stack-interview-questions-and-answers'>FullStack.Cafe</a>
14596 | 
14597 | #### Q49: Why should you separate Express 'app' and 'server'? ⭐⭐⭐⭐⭐
14598 | **Answer:**
14599 | Read Full Answer on 👉 <a href='https://www.fullstack.cafe\blog\top-60-mean-stack-interview-questions-and-answers'>FullStack.Cafe</a>
14600 | 
14601 | #### Q50: What is the difference between Classes and Interfaces in Typescript? ⭐⭐
14602 | **Answer:**
14603 | We use classes as object factories. A class defines a blueprint of what an object should look like and act like and then implements that blueprint by initialising class properties and defining methods. Classes are present throughout all the phases of our code.
14604 | 
14605 | Unlike classes, an interface is a virtual structure that only exists within the context of TypeScript. The TypeScript compiler uses interfaces solely for type-checking purposes. Once code is transpiled to its target language, it will be stripped from interfaces.
14606 | 
14607 | A class may define a factory or a singleton by providing initialisation to its properties and implementation to its methods, an interface is simply a structural contract that defines what the properties of an object should have as a name and as a type.
14608 | 
14609 | **Source:** _toddmotto.com_
14610 | 
14611 | #### Q51: What is "Decorators" in TypeScript? ⭐⭐
14612 | **Answer:**
14613 | A *Decorator* is a special kind of declaration that can be attached to a class declaration, method, accessor, property, or parameter. Decorators are functions that take their target as the argument. With decorators we can run arbitrary code around the target execution or even entirely replace the target with a new definition.
14614 | 
14615 | There are 4 things we can decorate in ECMAScript2016 (and Typescript): constructors, methods, properties and parameters. 
14616 | 
14617 | **Source:** _www.sparkbit.pl_
14618 | 
14619 | #### Q52: Does TypeScript support all object oriented principles? ⭐⭐
14620 | **Answer:**
14621 | The answer is **YES**. There are 4 main principles to Object Oriented Programming: 
14622 | 
14623 | * Encapsulation, 
14624 | * Inheritance, 
14625 | * Abstraction, and 
14626 | * Polymorphism. 
14627 | 
14628 | TypeScript can implement all four of them with its smaller and cleaner syntax.
14629 | 
14630 | **Source:** _jonathanmh.com_
14631 | 
14632 | #### Q53: How TypeScript is optionally statically typed language? ⭐⭐⭐
14633 | **Answer:**
14634 | TypeScript is referred as *optionally statically typed*, which means you can ask the compiler to ignore the type of a variable. Using `any` data type, we can assign any type of value to the variable. TypeScript will not give any error checking during compilation.
14635 | 
14636 | Consider:
14637 | ```js
14638 | var unknownType: any = 4;
14639 | unknownType = "Okay, I am a string";
14640 | unknownType = false; // A boolean.
14641 | ```
14642 | 
14643 | **Source:** _http://www.talkingdotnet.com_
14644 | 
14645 | #### Q54: What is the difference between "interface vs type" statements? ⭐⭐⭐⭐
14646 | **Details:**
14647 | ```js
14648 | interface X {
14649 |     a: number
14650 |     b: string
14651 | }
14652 | 
14653 | type X = {
14654 |     a: number
14655 |     b: string
14656 | };
14657 | ```
14658 | 
14659 | **Answer:**
14660 | Read Full Answer on 👉 <a href='https://www.fullstack.cafe\blog\top-60-mean-stack-interview-questions-and-answers'>FullStack.Cafe</a>
14661 | 
14662 | #### Q55: How would you overload a class constructor in TypeScript? ⭐⭐⭐⭐
14663 | **Answer:**
14664 | Read Full Answer on 👉 <a href='https://www.fullstack.cafe\blog\top-60-mean-stack-interview-questions-and-answers'>FullStack.Cafe</a>
14665 | 
14666 | #### Q56: What is CORS and how to enable one? ⭐⭐
14667 | **Answer:**
14668 | A request for a resource (like an image or a font) outside of the origin is known as a *cross-origin request*. CORS (cross-origin resource sharing) manages cross-origin requests. CORS allows servers to specify who (i.e., which origins) can access the assets on the server, among many other things.
14669 | 
14670 | **Access-Control-Allow-Origin** is an HTTP header that defines which foreign origins are allowed to access the content of pages on your domain via scripts using methods such as XMLHttpRequest. 
14671 | 
14672 | For example, if your server provides both a website and an API intended for XMLHttpRequest access on a remote websites, only the API resources should return the Access-Control-Allow-Origin header. Failure to do so will allow foreign origins to read the contents of any page on your origin.
14673 | 
14674 | ```sh
14675 | # Allow any site to read the contents of this JavaScript library, so that subresource integrity works
14676 | Access-Control-Allow-Origin: *
14677 | ```
14678 | 
14679 | **Source:** _infosec.mozilla.org_
14680 | 
14681 | #### Q57: What is Cross Site Scripting (XSS)? ⭐⭐
14682 | **Answer:**
14683 | By using **Cross Site Scripting (XSS)** technique, users executed malicious scripts (also called payloads) unintentionally by clicking on untrusted links and hence, these scripts pass cookies information to attackers.
14684 | 
14685 | **Source:** _allabouttesting.org_
14686 | 
14687 | #### Q58: What is ClickJacking? ⭐⭐⭐
14688 | **Answer:**
14689 | **ClickJacking** is an attack that fools users into thinking they are clicking on one thing when they are actually clicking on another. The attack is possible thanks to HTML frames (iframes). 
14690 | 
14691 | Its other name, user interface (UI) redressing, better describes what is going on. Users think they are using a web page’s normal UI, but in fact there is a hidden UI in control; in other words, the UI has been redressed. When users click something they think is safe, the hidden UI performs a different action.
14692 | 
14693 | **Source:** _synopsys.com_
14694 | 
14695 | #### Q59: What is Cross-Site Request Forgery? ⭐⭐⭐
14696 | **Answer:**
14697 | **Cross-Site Request Forgery (CSRF)** is an attack that forces authenticated users to submit a request to a Web application against which they are currently authenticated. 
14698 | 
14699 | A CSRF attack tricks the victim into clicking a URL that contains a maliciously crafted, unauthorized request for a particular Web application. The user’s browser then sends this maliciously crafted request to a targeted Web application. The request also includes any credentials related to the particular website (e.g., user session cookies). If the user is in an active session with a targeted Web application, the application treats this new request as an authorized request submitted by the user.
14700 | 
14701 | **How to prevent**
14702 | 
14703 | To defeat a CSRF attack, applications need a way to determine if the HTTP request is legitimately generated via the application’s user interface. The best way to achieve this is through a CSRF token. A CSRF token is a secure random token (e.g., synchronizer token or challenge token) that is used to prevent CSRF attacks. The token needs to be unique per user session and should be of large random value to make it difficult to guess.
14704 | 
14705 | **Source:** _synopsys.com_
14706 | 
14707 |

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