Big-O Performance

; 243 | } 244 | } 245 | ``` 246 | 247 | **This is not required for React** but many people find this feature convenient. You can read about the benefits of this approach [here](https://medium.com/seek-ui-engineering/block-element-modifying-your-javascript-components-d7f99fcab52b). However you should be aware that this makes your code less portable to other build tools and environments than Webpack. 248 | 249 | In development, expressing dependencies this way allows your styles to be reloaded on the fly as you edit them. In production, all CSS files will be concatenated into a single minified `.css` file in the build output. 250 | 251 | If you are concerned about using Webpack-specific semantics, you can put all your CSS right into `src/index.css`. It would still be imported from `src/index.js`, but you could always remove that import if you later migrate to a different build tool. 252 | 253 | ## Post-Processing CSS 254 | 255 | This project setup minifies your CSS and adds vendor prefixes to it automatically through [Autoprefixer](https://github.com/postcss/autoprefixer) so you don’t need to worry about it. 256 | 257 | For example, this: 258 | 259 | ```css 260 | .App { 261 | display: flex; 262 | flex-direction: row; 263 | align-items: center; 264 | } 265 | ``` 266 | 267 | becomes this: 268 | 269 | ```css 270 | .App { 271 | display: -webkit-box; 272 | display: -ms-flexbox; 273 | display: flex; 274 | -webkit-box-orient: horizontal; 275 | -webkit-box-direction: normal; 276 | -ms-flex-direction: row; 277 | flex-direction: row; 278 | -webkit-box-align: center; 279 | -ms-flex-align: center; 280 | align-items: center; 281 | } 282 | ``` 283 | 284 | There is currently no support for preprocessors such as Less, or for sharing variables across CSS files. 285 | 286 | ## Adding Images and Fonts 287 | 288 | With Webpack, using static assets like images and fonts works similarly to CSS. 289 | 290 | You can **`import` an image right in a JavaScript module**. This tells Webpack to include that image in the bundle. Unlike CSS imports, importing an image or a font gives you a string value. This value is the final image path you can reference in your code. 291 | 292 | Here is an example: 293 | 294 | ```js 295 | import React from 'react'; 296 | import logo from './logo.png'; // Tell Webpack this JS file uses this image 297 | 298 | console.log(logo); // /logo.84287d09.png 299 | 300 | function Header() { 301 | // Import result is the URL of your image 302 | return

; 303 | } 304 | 305 | export default function Header; 306 | ``` 307 | 308 | This works in CSS too: 309 | 310 | ```css 311 | .Logo { 312 | background-image: url(./logo.png); 313 | } 314 | ``` 315 | 316 | Webpack finds all relative module references in CSS (they start with `./`) and replaces them with the final paths from the compiled bundle. If you make a typo or accidentally delete an important file, you will see a compilation error, just like when you import a non-existent JavaScript module. The final filenames in the compiled bundle are generated by Webpack from content hashes. If the file content changes in the future, Webpack will give it a different name in production so you don’t need to worry about long-term caching of assets. 317 | 318 | Please be advised that this is also a custom feature of Webpack. 319 | 320 | **It is not required for React** but many people enjoy it (and React Native uses a similar mechanism for images). However it may not be portable to some other environments, such as Node.js and Browserify. If you prefer to reference static assets in a more traditional way outside the module system, please let us know [in this issue](https://github.com/facebookincubator/create-react-app/issues/28), and we will consider support for this. 321 | 322 | ## Adding Bootstrap 323 | 324 | You don’t have to use [React Bootstrap](https://react-bootstrap.github.io) together with React but it is a popular library for integrating Bootstrap with React apps. If you need it, you can integrate it with Create React App by following these steps: 325 | 326 | Install React Bootstrap and Bootstrap from NPM. React Bootstrap does not include Bootstrap CSS so this needs to be installed as well: 327 | 328 | ``` 329 | npm install react-bootstrap --save 330 | npm install bootstrap@3 --save 331 | ``` 332 | 333 | Import Bootstrap CSS and optionally Bootstrap theme CSS in the ```src/index.js``` file: 334 | 335 | ```js 336 | import 'bootstrap/dist/css/bootstrap.css'; 337 | import 'bootstrap/dist/css/bootstrap-theme.css'; 338 | ``` 339 | 340 | Import required React Bootstrap components within ```src/App.js``` file or your custom component files: 341 | 342 | ```js 343 | import { Navbar, Jumbotron, Button } from 'react-bootstrap'; 344 | ``` 345 | 346 | Now you are ready to use the imported React Bootstrap components within your component hierarchy defined in the render method. Here is an example [`App.js`](https://gist.githubusercontent.com/gaearon/85d8c067f6af1e56277c82d19fd4da7b/raw/6158dd991b67284e9fc8d70b9d973efe87659d72/App.js) redone using React Bootstrap. 347 | 348 | ## Adding Flow 349 | 350 | Flow typing is currently [not supported out of the box](https://github.com/facebookincubator/create-react-app/issues/72) with the default `.flowconfig` generated by Flow. If you run it, you might get errors like this: 351 | 352 | ```js 353 | node_modules/fbjs/lib/Deferred.js.flow:60 354 | 60: Promise.prototype.done.apply(this._promise, arguments); 355 | ^^^^ property `done`. Property not found in 356 | 495: declare class Promise<+R> { 357 | ^ Promise. See lib: /private/tmp/flow/flowlib_34952d31/core.js:495 358 | 359 | node_modules/fbjs/lib/shallowEqual.js.flow:29 360 | 29: return x !== 0 || 1 / (x: $FlowIssue) === 1 / (y: $FlowIssue); 361 | ^^^^^^^^^^ identifier `$FlowIssue`. Could not resolve name 362 | 363 | src/App.js:3 364 | 3: import logo from './logo.svg'; 365 | ^^^^^^^^^^^^ ./logo.svg. Required module not found 366 | 367 | src/App.js:4 368 | 4: import './App.css'; 369 | ^^^^^^^^^^^ ./App.css. Required module not found 370 | 371 | src/index.js:5 372 | 5: import './index.css'; 373 | ^^^^^^^^^^^^^ ./index.css. Required module not found 374 | ``` 375 | 376 | To fix this, change your `.flowconfig` to look like this: 377 | 378 | ```ini 379 | [libs] 380 | ./node_modules/fbjs/flow/lib 381 | 382 | [options] 383 | esproposal.class_static_fields=enable 384 | esproposal.class_instance_fields=enable 385 | 386 | module.name_mapper='^$.*$\.css$' -> 'react-scripts/config/flow/css' 387 | module.name_mapper='^$.*$\.$jpg\|png\|gif\|eot\|otf\|webp\|svg\|ttf\|woff\|woff2\|mp4\|webm$$' -> 'react-scripts/config/flow/file' 388 | 389 | suppress_type=$FlowIssue 390 | suppress_type=$FlowFixMe 391 | ``` 392 | 393 | Re-run flow, and you shouldn’t get any extra issues. 394 | 395 | If you later `eject`, you’ll need to replace `react-scripts` references with the `` placeholder, for example: 396 | 397 | ```ini 398 | module.name_mapper='^$.*$\.css$' -> '/config/flow/css' 399 | module.name_mapper='^$.*$\.$jpg\|png\|gif\|eot\|otf\|webp\|svg\|ttf\|woff\|woff2\|mp4\|webm$$' -> '/config/flow/file' 400 | ``` 401 | 402 | We will consider integrating more tightly with Flow in the future so that you don’t have to do this. 403 | 404 | ## Adding Custom Environment Variables 405 | 406 | >Note: this feature is available with `react-scripts@0.2.3` and higher. 407 | 408 | Your project can consume variables declared in your environment as if they were declared locally in your JS files. By 409 | default you will have `NODE_ENV` defined for you, and any other environment variables starting with 410 | `REACT_APP_`. These environment variables will be defined for you on `process.env`. For example, having an environment 411 | variable named `REACT_APP_SECRET_CODE` will be exposed in your JS as `process.env.REACT_APP_SECRET_CODE`, in addition 412 | to `process.env.NODE_ENV`. 413 | 414 | These environment variables can be useful for displaying information conditionally based on where the project is 415 | deployed or consuming sensitive data that lives outside of version control. 416 | 417 | First, you need to have environment variables defined, which can vary between OSes. For example, let's say you wanted to 418 | consume a secret defined in the environment inside a ` 429 | ); 430 | } 431 | ``` 432 | 433 | The above form is looking for a variable called `REACT_APP_SECRET_CODE` from the environment. In order to consume this 434 | value, we need to have it defined in the environment: 435 | 436 | ### Windows (cmd.exe) 437 | 438 | ```cmd 439 | set REACT_APP_SECRET_CODE=abcdef&&npm start 440 | ``` 441 | 442 | (Note: the lack of whitespace is intentional.) 443 | 444 | ### Linux, OS X (Bash) 445 | 446 | ```bash 447 | REACT_APP_SECRET_CODE=abcdef npm start 448 | ``` 449 | 450 | > Note: Defining environment variables in this manner is temporary for the life of the shell session. Setting 451 | permanent environment variables is outside the scope of these docs. 452 | 453 | With our environment variable defined, we start the app and consume the values. Remember that the `NODE_ENV` 454 | variable will be set for you automatically. When you load the app in the browser and inspect the ``, you will see 455 | its value set to `abcdef`, and the bold text will show the environment provided when using `npm start`: 456 | 457 | ```html 458 |

459 | You are running this application in development mode. 460 | 463 |

464 | ``` 465 | 466 | Having access to the `NODE_ENV` is also useful for performing actions conditionally: 467 | 468 | ```js 469 | if (process.env.NODE_ENV !== 'production') { 470 | analytics.disable(); 471 | } 472 | ``` 473 | 474 | ## Integrating with a Node Backend 475 | 476 | Check out [this tutorial](https://www.fullstackreact.com/articles/using-create-react-app-with-a-server/) for instructions on integrating an app with a Node backend running on another port, and using `fetch()` to access it. You can find the companion GitHub repository [here](https://github.com/fullstackreact/food-lookup-demo). 477 | 478 | ## Proxying API Requests in Development 479 | 480 | >Note: this feature is available with `react-scripts@0.2.3` and higher. 481 | 482 | People often serve the front-end React app from the same host and port as their backend implementation. 483 | For example, a production setup might look like this after the app is deployed: 484 | 485 | ``` 486 | / - static server returns index.html with React app 487 | /todos - static server returns index.html with React app 488 | /api/todos - server handles any /api/* requests using the backend implementation 489 | ``` 490 | 491 | Such setup is **not** required. However, if you **do** have a setup like this, it is convenient to write requests like `fetch('/api/todos')` without worrying about redirecting them to another host or port during development. 492 | 493 | To tell the development server to proxy any unknown requests to your API server in development, add a `proxy` field to your `package.json`, for example: 494 | 495 | ```js 496 | "proxy": "http://localhost:4000", 497 | ``` 498 | 499 | This way, when you `fetch('/api/todos')` in development, the development server will recognize that it’s not a static asset, and will proxy your request to `http://localhost:4000/api/todos` as a fallback. 500 | 501 | Conveniently, this avoids [CORS issues](http://stackoverflow.com/questions/21854516/understanding-ajax-cors-and-security-considerations) and error messages like this in development: 502 | 503 | ``` 504 | Fetch API cannot load http://localhost:4000/api/todos. No 'Access-Control-Allow-Origin' header is present on the requested resource. Origin 'http://localhost:3000' is therefore not allowed access. If an opaque response serves your needs, set the request's mode to 'no-cors' to fetch the resource with CORS disabled. 505 | ``` 506 | 507 | Keep in mind that `proxy` only has effect in development (with `npm start`), and it is up to you to ensure that URLs like `/api/todos` point to the right thing in production. You don’t have to use the `/api` prefix. Any unrecognized request will be redirected to the specified `proxy`. 508 | 509 | Currently the `proxy` option only handles HTTP requests, and it won’t proxy WebSocket connections. 510 | If the `proxy` option is **not** flexible enough for you, alternatively you can: 511 | 512 | * Enable CORS on your server ([here’s how to do it for Express](http://enable-cors.org/server_expressjs.html)). 513 | * Use [environment variables](#adding-custom-environment-variables) to inject the right server host and port into your app. 514 | 515 | ## Deployment 516 | 517 | By default, Create React App produces a build assuming your app is hosted at the server root. 518 | To override this, specify the `homepage` in your `package.json`, for example: 519 | 520 | ```js 521 | "homepage": "http://mywebsite.com/relativepath", 522 | ``` 523 | 524 | This will let Create React App correctly infer the root path to use in the generated HTML file. 525 | 526 | ### Now 527 | 528 | See [this example](https://github.com/xkawi/create-react-app-now) for a zero-configuration single-command deployment with [now](https://zeit.co/now). 529 | 530 | ### Heroku 531 | 532 | Use the [Heroku Buildpack for Create React App](https://github.com/mars/create-react-app-buildpack). 533 | You can find instructions in [Deploying React with Zero Configuration](https://blog.heroku.com/deploying-react-with-zero-configuration). 534 | 535 | ### Surge 536 | 537 | Install the Surge CLI if you haven't already by running `npm install -g surge`. Run the `surge` command and log in you or create a new account. You just need to specify the *build* folder and your custom domain, and you are done. 538 | 539 | ```sh 540 | email: email@domain.com 541 | password: ******** 542 | project path: /path/to/project/build 543 | size: 7 files, 1.8 MB 544 | domain: create-react-app.surge.sh 545 | upload: [====================] 100%, eta: 0.0s 546 | propagate on CDN: [====================] 100% 547 | plan: Free 548 | users: email@domain.com 549 | IP Address: X.X.X.X 550 | 551 | Success! Project is published and running at create-react-app.surge.sh 552 | ``` 553 | 554 | Note that in order to support routers that use html5 `pushState` API, you may want to rename the `index.html` in your build folder to `200.html` before deploying to Surge. This [ensures that every URL falls back to that file](https://surge.sh/help/adding-a-200-page-for-client-side-routing). 555 | 556 | ### GitHub Pages 557 | 558 | >Note: this feature is available with `react-scripts@0.2.0` and higher. 559 | 560 | Open your `package.json` and add a `homepage` field: 561 | 562 | ```js 563 | "homepage": "http://myusername.github.io/my-app", 564 | ``` 565 | 566 | **The above step is important!** 567 | Create React App uses the `homepage` field to determine the root URL in the built HTML file. 568 | 569 | Now, whenever you run `npm run build`, you will see a cheat sheet with a sequence of commands to deploy to GitHub pages: 570 | 571 | ```sh 572 | git commit -am "Save local changes" 573 | git checkout -B gh-pages 574 | git add -f build 575 | git commit -am "Rebuild website" 576 | git filter-branch -f --prune-empty --subdirectory-filter build 577 | git push -f origin gh-pages 578 | git checkout - 579 | ``` 580 | 581 | You may copy and paste them, or put them into a custom shell script. You may also customize them for another hosting provider. 582 | 583 | Note that GitHub Pages doesn't support routers that use the HTML5 `pushState` history API under the hood (for example, React Router using `browserHistory`). This is because when there is a fresh page load for a url like `http://user.github.io/todomvc/todos/42`, where `/todos/42` is a frontend route, the GitHub Pages server returns 404 because it knows nothing of `/todos/42`. If you want to add a router to a project hosted on GitHub Pages, here are a couple of solutions: 584 | * You could switch from using HTML5 history API to routing with hashes. If you use React Router, you can switch to `hashHistory` for this effect, but the URL will be longer and more verbose (for example, `http://user.github.io/todomvc/#/todos/42?_k=yknaj`). [Read more](https://github.com/reactjs/react-router/blob/master/docs/guides/Histories.md#histories) about different history implementations in React Router. 585 | * Alternatively, you can use a trick to teach GitHub Pages to handle 404 by redirecting to your `index.html` page with a special redirect parameter. You would need to add a `404.html` file with the redirection code to the `build` folder before deploying your project, and you’ll need to add code handling the redirect parameter to `index.html`. You can find a detailed explanation of this technique [in this guide](https://github.com/rafrex/spa-github-pages). 586 | 587 | ## Something Missing? 588 | 589 | If you have ideas for more “How To” recipes that should be on this page, [let us know](https://github.com/facebookincubator/create-react-app/issues) or [contribute some!](https://github.com/facebookincubator/create-react-app/edit/master/template/README.md) 590 | --------------------------------------------------------------------------------

Big-O Notation Analyzer

Big O Calculations

Sample Big O Graphs

O(1) - Constant

O(log n) - Logarithmic

O(n) - Linear

O(n^2) - Quadratic

O(c^n) - Exponential

O(n!) - Factorial