└── README.md


/README.md:
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  1 | # JavaScript-Array-Interview-Practice
  2 | 
  3 | #Question1 
  4 | ##Create an Array object.
  5 | ```
  6 | Method 1
  7 | 
  8 | var fruits = ['Apple', 'Banana'];
  9 | console.log(fruits) // [ 'Apple', 'Banana' ]
 10 | ```
 11 | ```
 12 | Method 2
 13 | 
 14 | var msgArray = [];
 15 | msgArray[0] = 'Hello';
 16 | console.log(msgArray) //  [ 'Hello' ]
 17 | ```
 18 | ```
 19 | Method 3 
 20 | 
 21 | var array = new Array('Hello');
 22 | console.log(array) // [ 'Hello' ]
 23 | ```
 24 | ```
 25 | Method 4 
 26 | 
 27 | var another = Array.of(1, 2, 3);
 28 | console.log(another) // [ 1, 2, 3 ]
 29 | ```
 30 | ```
 31 | Method 5 
 32 | 
 33 | var b = arrayMaker({7: 1}, {2: 3});
 34 | 
 35 | function arrayMaker(n) {
 36 |   console.log(n);
 37 |   if (n !== typeof Array) {
 38 |     return Array.prototype.slice.call(arguments);
 39 |   }
 40 | }
 41 |  
 42 | console.log(b) //  [ { '7': 1 }, { '2': 3 } ]
 43 | ```
 44 | 
 45 | #Question 2 
 46 | 
 47 | ##Take this array var array = [1,2,3,4,5] and copy it using
 48 | 
 49 | 	
 50 |   >the slice method and the for loop method
 51 | 	 
 52 | 
 53 | ```
 54 | Method 1 - The slice method
 55 | 
 56 | var array = [1,2,3,4,5,6];
 57 | 
 58 | var result = array.slice();  // to copy an array to new array
 59 | 
 60 | console.log(array);  // [1,2,3,4,5,6]
 61 | console.log(result); // [1,2,3,4,5,6]
 62 | ```
 63 | ```
 64 | Method 2 - The for loop method
 65 | 
 66 | var array = [1, 2, 3, 4, 5, 6];
 67 | Var array2 = [ ];
 68 | 
 69 | for (var i = 0; i < array.length; ++i) {
 70 | 
 71 |   array2[i] = array[i];
 72 | }
 73 | 
 74 | console.log (array2); // [ 1, 2, 3, 4, 5, 6 ]
 75 | ```
 76 | 
 77 | #Question 3
 78 | 
 79 | ##Empty this array var array = [1,2,3,4,5]
 80 | 
 81 | ```
 82 | Method 1 
 83 | 
 84 | Var array = [1,2,3,4,5];
 85 | 
 86 | Array = [ ];
 87 | ```
 88 | N.B
 89 | >This is only recommended if you don't have any other references to this array because it will actually create a new empty array and the other reference will still be available to others in memory.
 90 | 
 91 | 
 92 | ```
 93 | EXAMPLE
 94 | var array = [1,2,3,4,5];
 95 | var array2 = array;
 96 | 
 97 | array = [ ];
 98 | 
 99 | console.log(array);  // [ ];
100 | console.log(array2); // [ 1, 2, 3, 4, 5 ]
101 | ```
102 | 
103 | ```
104 | Method 2 
105 | var array3 = [1,2,3,4,5];
106 | array3.length = 0
107 | console.log(array3);  // [ ];
108 | ```
109 | NB
110 | >This even empties to referenced arrays
111 | 
112 | ```
113 | var array3 = [1,2,3,4,5];
114 | var array4 = array3;
115 | array3.length = 0;
116 | console.log(array3);  // [ ];
117 | console.log(array4);  // [ ];
118 | ```
119 | ```
120 | Method 3
121 | var array5 = [1,2,3,4,5];
122 | array5.splice(0,array5.length);
123 | console.log(array5);  // [ ];
124 | ```
125 | ```
126 | Method 4 
127 | var array6 = [1,2,3,4,5];
128 | console.log(array6);  // [1,2,3,4,5]
129 | 
130 | function emptyArray(array){
131 |   'use strict';
132 |     while(array.length){
133 |      array6.pop();
134 | }
135 | }
136 | 
137 | emptyArray(array6);  // call function
138 | console.log(array6);  // [ ] ; now empty
139 | ```
140 | 
141 | #Question 4
142 | ##What type is an Array set to?
143 | ```
144 | Var array3 = [1,2,3,4,5];
145 | console.log(typeof(array3));  // Object 
146 | ```
147 | 
148 | #Question 5
149 | ##How can you check if something is an Array?
150 | 
151 | ```
152 | Method 1
153 | 
154 | var check = [1, 2, 3];
155 | var a = Array.isArray([1, 2, 3]);
156 | var b = Array.isArray({
157 |   foo: 123
158 | });
159 | var c = Array.isArray('foobar');
160 | var d = Array.isArray(undefined);
161 | var e = Array.isArray(check);
162 | 
163 | console.log(a); // true
164 | console.log(b); // false
165 | console.log(c); // false
166 | console.log(d); // false
167 | console.log(e); // true
168 | ```
169 | 
170 | ```
171 | Method 2
172 | 
173 | function checkIfArray(array) {
174 |   'use strict';
175 |   
176 |   if (Object.prototype.toString.call(array) === '[object Array]') {
177 |     console.log('array it is  ');
178 |   } else {
179 |     console.log('array it is Not ');
180 |   }
181 | }
182 | 
183 | var array2 = 'testing';
184 | checkIfArray(array2);  // array it is Not
185 | var array3 = [1,2,3,4,5];
186 | checkIfArray(array3); //array it is 
187 | ```
188 | 
189 | ```
190 | Method 3 
191 | 
192 | var array = [1, 2, 3, 4, 5];
193 | 
194 | function checkIfArray(object) {
195 |   'use strict';
196 |   if (typeof object === 'string') {
197 |     console.log('array it is NOT ');
198 |   } else {
199 |     console.log('array it is ');
200 |   }
201 | }
202 | 
203 | checkIfArray(array);  //array it is
204 | ```
205 | 
206 | 
207 | #Question 6
208 | ##Add an item to the end of an array.
209 | ```
210 | Method 1 
211 | var array = ['a','b','c'];
212 | 
213 | array.push('d');
214 | console.log(array); // [ 'a', 'b', 'c', 'd' ]
215 | ```
216 | ```
217 | Method 2
218 | array[array.length] = 'e';
219 | console.log(array); // [ 'a', 'b', 'c', 'd', 'e' ]
220 | ```
221 | 
222 | #Question 7
223 | ##Find the index position of d in this array 
224 | var arr= ['a','b','c','d'];
225 | 
226 | ``
227 | Answer : console.log(arr.indexOf('d'));  // 3
228 | ``
229 | 
230 | #Question 8
231 | ##What will be returned if you look for the index of something that does not exist?
232 | 
233 | ``
234 | var arr= ['a','b','c','d'];
235 | console.log(arr.indexOf(7)); // -1 === does not exist
236 | ``
237 | 
238 | 
239 | #Question 9 
240 | ##Write a function to check if milk exists in your array
241 | var items = ['milk', 'bread', 'sugar'];
242 | 
243 | Answer
244 | 
245 | ```
246 | var items = ['milk', 'bread', 'sugar'];
247 | 
248 | function checkForProduct(item){
249 |    
250 |     if (items.indexOf(item) === -1) {
251 |    
252 |     console.log('item does not exist');
253 | } else {
254 | 
255 |     console.log('item is in your list');
256 | 
257 | }
258 | }
259 | 
260 | checkForProduct('socks'); //item does not exist
261 | checkForProduct('milk'); //item is in your list
262 | ```
263 | 
264 | 
265 | 
266 | 
267 | 
268 | #Question 10
269 | ##Now you've found milk exists add some code to find the index of milk and remove that item.
270 | 
271 | ```
272 | var items = ['milk', 'bread', 'sugar'];
273 | 
274 | //find index of item if it exists
275 | var a = items.indexOf('milk');
276 | console.log(a); // 0
277 | 
278 | //remove that index from array 
279 | items.splice(0,1);
280 | console.log(items); // [ 'bread', 'sugar']
281 | ```
282 | 
283 | #Question 11
284 | ##List the ways to loop over an array.
285 | 
286 | 
287 | >For Each
288 | 
289 | >For in
290 | 
291 | >For loop
292 | 
293 | 
294 | 
295 | 
296 | 
297 | 
298 | 
299 | #Question 12
300 | ##Write some code to put these numbers in order
301 | var numbers = [1, 12, 2 ,23,77,7,33,5,99,234,];
302 | 
303 | ```
304 | var numbers2 = [1, 12, 2 ,23,77,7,33,5,99,234];
305 | var numbers3 = numbers2.sort((a, b) => {
306 |    return a - b;
307 | });
308 | 
309 | console.log(numbers3); // [ 1, 2, 5, 7, 12, 23, 33, 77, 99, 234 ]
310 | ```
311 | 
312 | #Question 13
313 | ##Write some code to place this list in alphabetical order
314 | var p = ['a','z','e','y'];
315 | ```
316 | var p = ['a','z','e','y'];
317 | p.sort();
318 | console.log(p); // [ 'a', 'e', 'y', 'z' ]
319 | ```
320 | 
321 | #Question 14
322 | ##What is the length of these arrays 
323 | 
324 | ```
325 | A. var arr1 = [,,,]; 
326 | 
327 | B. var arr2 = new Array(3)
328 | 
329 | C. var arr3 = [1,2,3,4,5]
330 | 
331 | D. var array = [ [1,2,3], [4,5,6]  ];
332 | 
333 | E. var array[0].length = [ [1,2,3], [4,5,6]  ];
334 | 
335 | 
336 | Results
337 | 
338 | A. arr1.length = 3
339 | B. arr2.length = 3
340 | C. arr3.length = 5
341 | D. array.length = 2    counts the number of internal array
342 | E. array[0].length = 3 first internal array within the outer array
343 | ```
344 | 
345 | 
346 | 
347 | 
348 | 
349 | 
350 | 
351 | 
352 | #Question 15
353 | ##What are the results of these splice and slice methods
354 | 
355 | ```
356 | var a = ['zero', 'one', 'two', 'three'];
357 | var names = ['jason', 'john', 'peter', 'karen'];
358 | 
359 | var sliced = a.slice(1, 3);
360 | var spliced = names.splice(1,3);
361 | 
362 | 
363 | The slice() method returns a shallow copy of a portion of an array into a new array object selected from begin to end (end not included). The original array will not be modified.
364 | 
365 | console.log(sliced); // creates a new array ['one', 'two'] 
366 | console.log(a); // main array remains untouched 
367 | 
368 | The splice() method changes the content of an array by removing existing elements and/or adding new elements.
369 | 
370 | console.log(spliced); // it returns  [ 'john', 'peter', 'karen' ] 
371 | console.log(names); // however the array only contains jason now
372 | 
373 | ```
374 | 
375 | #Question 16
376 | ##What are the console logs of these shift and unshift methods
377 | 
378 | ```
379 | Var a = [ ] ; 
380 | 
381 | We take an empty array and 
382 | 
383 | a.unshift(1);
384 | var a = console.log(a)
385 | a.unshift(22);
386 | var b = console.log(a)
387 | a.shift(); 
388 | var c = console.log(a)
389 | a.unshift(3,[4,5]); 
390 | var d = console.log(a)
391 | a.shift(); 
392 | var e = console.log(a)
393 | a.shift();
394 | var f = console.log(a)
395 | a.shift();
396 | var g = console.log(a)
397 | Results
398 | 
399 | Var a = [ 1 ]       // we a.unshift(1) so added 1 to front
400 | 
401 | Var b = [ 22, 1 ]   // we a.unshift(22) so added 22 to front
402 | 
403 | Var c = [ 1 ]       // we a.shift() so removed the first element
404 | 
405 | Var d = [ 3, [ 4, 5 ], 1 ]   // we a.unshift(3,[4,5]) so added  
406 |                                 these to front
407 | Var e = [ [ 4, 5 ], 1 ]   // we a.shift() so remove first element
408 | 
409 | Var f = [ 1 ]   // we a.shift() so remove first element
410 | 
411 | Var g = [ ]   // we a.shift() so remove first element leaving it
412 |                  empty        
413 | ```
414 | 
415 | 
416 | #Question 17
417 | 
418 | ##Using reduce add all these numbers
419 |  var numbers = [1, 2, 3, 4, 5, 6];
420 | 
421 | ```
422 | var numbers = [1, 2, 3, 4, 5, 6];
423 | 
424 | var total = numbers.reduce((a, b) => {
425 |   return a + b;
426 | });
427 | 
428 | console.log(total); // Total returned is : 21
429 | ```
430 | 
431 | #Question 18
432 | ##Flatten this array to one single array using reduce
433 | Var array =  [[0, 1], [2, 3], [4, 5]];
434 | 
435 | ```
436 | Var array =  [[0, 1], [2, 3], [4, 5]];
437 | 
438 | var flattened = array.reduce(function(a, b) {
439 |     return a.concat(b);
440 | },[ ]);
441 | 
442 | console.log(flattened); // [ 0, 1, 2, 3, 4, 5 ]
443 | ```
444 | 
445 | #Question 19
446 | ##Filter this array to return just the dogs
447 | 
448 | ```
449 | var animals = [
450 |     { name: "Jason", species:"rabbit"},
451 |     { name: "Jessica", species:"dog"},
452 |     { name: "Jacky", species:"owl"},
453 |     { name: "Luke", species:"fish"},
454 |     { name: "Junior", species:"rat"},
455 |     { name: "Thomas", species:"cat"}
456 | ]
457 | Answer
458 | 
459 | /******************************************
460 |    filter method with callback function
461 | ******************************************/
462 | 
463 | var dogs = animals.filter(function(animals){
464 |     return animals.species === "dog";
465 | });
466 | 
467 | console.log(dogs);
468 | 
469 | Returns
470 | 
471 | [ { name: 'Jessica', species: 'dog' }]
472 | 
473 | The filter() method creates a new array with all elements that pass the test implemented by the provided function.
474 | ```
475 | 
476 | 
477 | 
478 | 
479 | #Question 20
480 | ##Using array in question 19 use map function to return all the species
481 | ```
482 | var types = animals.map(function(animals){
483 |     return animals.species;
484 | });
485 | console.log(types); // [ 'rabbit', 'dog', 'owl', 'fish', 'rat', 'cat' ]
486 | ```
487 | 


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