├── README.md
└── audio-visuals
    ├── .gitignore
    ├── README.md
    ├── package.json
    ├── public
        ├── favicon.ico
        └── index.html
    ├── src
        ├── App.css
        ├── App.js
        ├── App.test.js
        ├── index.css
        ├── index.js
        └── logo.svg
    └── yarn.lock


/README.md:
--------------------------------------------------------------------------------
  1 | # react-audio-visualization
  2 | 
  3 | This tutorial is for creating an audio visualization in React with the web audio API.
  4 | 
  5 | ### Let's get some stuff out of the way first,
  6 | 
  7 | In this tutorial will use Node.js and npm, if you already have that installed then that's great move on to the next step, otherwise [learn about // get npm here.](https://www.npmjs.com/get-npm)
  8 | 
  9 | This is *not* a tutorial on how to use React. If you want to learn more about how React works check out [Fullstack React](https://www.fullstackreact.com/)
 10 | 
 11 | The first thing we need to do is download create-react-app to get our react boilerplate. [Here are the docs if you want to learn more.](https://github.com/facebookincubator/create-react-app)
 12 | Type the following into your terminal:
 13 | 
 14 | ```
 15 | npm install -g create-react-app
 16 | ```
 17 | 
 18 | ### Okay now let's get started!
 19 | 
 20 | We can create our app by typing this command followed by the name of your application. I called mine audio-visuals in this example. Type the following into your terminal:
 21 | 
 22 | 
 23 | ```
 24 | create-react-app audio-visuals
 25 | ```
 26 | 
 27 | This may take a moment...
 28 | After it's done you can go ahead and change directories into the newly created app. Type the following into your terminal.
 29 | ```
 30 | cd audio-visuals
 31 | ```
 32 | 
 33 | Then open up the directory in your favorite text editor. \(I use Atom\) You can open it up from the terminal by typing
 34 | ```
 35 | atom .
 36 | ```
 37 | If you see an error that says atom is not a command then go to atom and look at the top menu bar. Click the drop down that says Atom and look for Install shell commands. Click that and you should now be able to use the atom command in your terminal.  
 38 | 
 39 | 
 40 | ![Atom menu example](http://i68.tinypic.com/avhjz7.png)
 41 | 
 42 | 
 43 |  Now that you've opened up the directory with your text editor, take a look around! Don't worry about the node modules or anything else that looks confusing. We will walk through this step by step.  
 44 | 
 45 | The file structure will look like this:  
 46 | ![File structure example](http://i64.tinypic.com/keao0i.png)
 47 | <!-- ```
 48 | audio-visuals/
 49 |   README.md
 50 |   node_modules/
 51 |   package.json
 52 |   .gitignore
 53 |   public/
 54 |     favicon.ico
 55 |     index.html
 56 |   src/
 57 |     App.css
 58 |     App.js
 59 |     App.test.js
 60 |     index.css
 61 |     index.js
 62 |     logo.svg
 63 | ``` -->
 64 | Navigate to audio-visuals/src/App.js
 65 |  you should see this in the file:
 66 | 
 67 | ```
 68 |  import React, { Component } from 'react';
 69 |  import logo from './logo.svg';
 70 |  import './App.css';
 71 | 
 72 |  class App extends Component {
 73 |    render() {
 74 |      return (
 75 |        <div className="App">
 76 |          <div className="App-header">
 77 |            <img src={logo} className="App-logo" alt="logo" />
 78 |            <h2>Welcome to React</h2>
 79 |          </div>
 80 |          <p className="App-intro">
 81 |            To get started, edit <code>src/App.js</code> and save to reload.
 82 |          </p>
 83 |        </div>
 84 |      );
 85 |    }
 86 |  }
 87 | 
 88 |  export default App;
 89 | ```
 90 |  You can delete some lines and leave it looking like this, or just paste the following code over it.
 91 | 
 92 |  ```
 93 |  import React, { Component } from 'react';
 94 |  import './App.css';
 95 | 
 96 |  class App extends Component {
 97 |    render() {
 98 |      return (
 99 |        <div className="App">
100 |        </div>
101 |      );
102 |    }
103 |  }
104 | 
105 |  export default App;
106 |  ```
107 | ### Now comes the real coding :)
108 | 
109 | Now inside the div with the className App we will insert an audio tag, with whatever song you'd like. I'm going to use sublime! Also add an h2 tag to say the name of the song and artist you choose.
110 | 
111 | now the App Component should look like this:
112 | 
113 | ```
114 | class App extends Component {
115 |   render() {
116 |     return (
117 |       <div className="App">
118 |       <h2>Sublime - 40oz to Freedom</h2>
119 |       <audio
120 |           ref="audio"
121 |           autoPlay={true}
122 |           controls={true}
123 |           src="https://p.scdn.co/mp3-preview/e4a8f30ca62b4d2a129cc4df76de66f43e12fa3f?cid=null"
124 |           >
125 |           </audio>
126 |       </div>
127 |     );
128 |   }
129 | }
130 | ```
131 | 
132 | As you can see we have set a few attributes on the audio tag, including the ref attribute. This is so we can reference the tag in a method we will write on our component later on. [Learn more about the ref attribute here!](https://facebook.github.io/react/docs/refs-and-the-dom.html)
133 | 
134 | You can now run ```npm start``` in your terminal and see the audio tag rendered on your webpage running on localhost:3000. Mine looks like this:  
135 | 
136 | 
137 | ![First website test](http://i67.tinypic.com/11t5sv8.png)  
138 | 
139 | Go back to atom or your text editor and add a canvas tag underneath the audio tag. Add a ref attribute of "analyzerCanvas" and an id of "analyzer". I've also added a couple divs with specific Ids so we can reference them later. Your app component should look like this now:
140 | 
141 | ```
142 | class App extends Component {
143 |     render() {
144 |         return (
145 |             <div className="App">
146 |                 <h2>Sublime - 40oz to Freedom</h2>
147 |                 <div id="mp3_player">
148 |                     <div id="audio_box">
149 |                         <audio
150 |                             ref="audio"
151 |                             autoPlay={true}
152 |                             controls={true}
153 |                             //this is the link to my song url feel free to use it or replace it with your own
154 |                             src={"https://p.scdn.co/mp3-preview/e4a8f30ca62b4d2a129cc4df76de66f43e12fa3f?cid=null"}
155 |                             >
156 |                             </audio>
157 |                         </div>
158 |                             <canvas
159 |                                 ref="analyzerCanvas"
160 |                                 id="analyzer"
161 |                                 >
162 |                                 </canvas>
163 |                     </div>
164 |                 </div>
165 |             );
166 |         }
167 |     }
168 | ```
169 | 
170 | Now we're going to add a method to the App component called createVisualization.
171 | inside that method we will create a new audio context with the Web Audio API. You do not need to download anything to have access to this API. An audio context represents an audio-processing graph, built from audio modules linked together, that are represented by AudioNodes. Just create a new instance by typing new AudioContext(); and save it to a variable. Later our audio context will be connected to our audio tag. So far our method looks like this
172 | 
173 | ```
174 | createVisualization(){
175 |     let context = new AudioContext();
176 | }
177 | ```
178 | Now that we have the Audio context object saved to a variable we can create an analyser node from it with the create analyser method. According to [the MDN documentation](https://developer.mozilla.org/en-US/docs/Web/API/AnalyserNode) an analyser node "represents a node able to provide real-time frequency and time-domain analysis information. It is an AudioNode that passes the audio stream unchanged from the input to the output, but allows you to take the generated data, process it, and create audio visualizations." If that sounds confusing it's okay you will still be able to move forward with the tutorial.
179 | 
180 | ```
181 | let analyser = context.createAnalyser();
182 | ```
183 | Then we create a reference to the canvas element and save it to a variable. We do this by accessing the refs object that React sets up for us by typing ```this.refs```. Then we want to get the context of the canvas so we can draw shapes on it. We do this with the methods that the canvas element has available for us to use.
184 | 
185 | ```
186 | let canvas = this.refs.analyserCanvas;
187 | let ctx = canvas.getContext('2d');
188 | ```
189 |  Now we want to grab the audio tag in the same way we did the canvas. Then we set the cross origin of the audio tag to anonymous
190 | 
191 |  ```
192 | let audio = this.refs.audio;
193 | audio.crossOrigin = "anonymous"
194 |  ```
195 | After that we pass the audio tag into the Audio context method called createMediaElementSource in order to create an audio source that the audio context can work with. Then we connect it to the audio context's analyser and then both the analyser and the audio source are connected to the context's destination.
196 | 
197 | ```
198 | let audioSrc = context.createMediaElementSource(audio);
199 | audioSrc.connect(analyser);
200 | audioSrc.connect(context.destination);
201 | analyser.connect(context.destination);
202 | ```
203 | #### Just to check in this is what App.js should look like so far:  
204 | 
205 | ```
206 | import React, { Component } from 'react';
207 | import './App.css';
208 | 
209 | class App extends Component {
210 | 
211 |     createVisualization(){
212 |         let context = new AudioContext();
213 |         let analyser = context.createAnalyser();
214 |         let canvas = this.refs.analyserCanvas;
215 |         let ctx = canvas.getContext('2d');
216 |         let audio = this.refs.audio;
217 |         audio.crossOrigin = "anonymous";
218 |         let audioSrc = context.createMediaElementSource(audio);
219 |         audioSrc.connect(analyser);
220 |         audioSrc.connect(context.destination);
221 |         analyser.connect(context.destination);
222 | 
223 |     }
224 | 
225 |     render() {
226 |         return (
227 |             <div className="App">
228 |                 <h2>Sublime - 40oz to Freedom</h2>
229 |                 <div id="mp3_player">
230 |                     <div id="audio_box">
231 |                         <audio
232 |                             ref="audio"
233 |                             autoPlay={true}
234 |                             controls={true}
235 |                             //this is the link to my song url feel free to use it or replace it with your own
236 |                             src={"https://p.scdn.co/mp3-preview/e4a8f30ca62b4d2a129cc4df76de66f43e12fa3f?cid=null"}
237 |                             >
238 |                             </audio>
239 |                         </div>
240 |                         <canvas
241 |                             ref="analyzerCanvas"
242 |                             id="analyzer"
243 |                             >
244 |                             </canvas>
245 |                         </div>
246 |                     </div>
247 |                 );
248 |             }
249 |         }
250 | 
251 |         export default App;
252 | ```
253 | 
254 | Now we will create a  recursive function called renderFrame within our createVisualization method and then we will invoke it.
255 | 
256 | ```
257 | function renderFrame(){
258 |     let freqData = new Uint8Array(analyser.frequencyBinCount)
259 |     requestAnimationFrame(renderFrame)
260 |     analyser.getByteFrequencyData(freqData)
261 |     ctx.clearRect(0, 0, canvas.width, canvas.height)
262 |     console.log(freqData)
263 |     ctx.fillStyle = '#9933ff';
264 |     let bars = 100;
265 |     for (var i = 0; i < bars; i++) {
266 |         let bar_x = i * 3;
267 |         let bar_width = 2;
268 |         let bar_height = -(freqData[i] / 2);
269 |         ctx.fillRect(bar_x, canvas.height, bar_width, bar_height)
270 |     }
271 | };
272 | renderFrame()
273 | ```
274 | 
275 | Here we are using some methods from analyser nodes to collect frequency data from the music playing and repeatedly draw bars on the canvas. The bars height depend on the audio's frequency. I made my bars purple but feel free to change the value of ctx.fillStyle to whatever color you want.
276 | 
277 | ### Almost done!
278 | 
279 | Now we need to make sure to invoke the createVisualization method after the app component loads. We will do this with a built in method called componentDidMount. This is called after the render function. Add this to your app component's methods.
280 | ```
281 | componentDidMount(){
282 |     this.createVisualization()
283 | }
284 | ```
285 | 
286 | Now we just need to bind the context of this to the createVisualization method so that when we say ```this``` we mean the app component, not the createVisualization method. We will do this in the constructor function.
287 | 
288 | ```
289 | constructor(props){
290 |     super(props)
291 | 
292 |     this.createVisualization = this.createVisualization.bind(this)
293 | }
294 | ```
295 | 
296 | ### Congratulations you're done! Run npm start in your terminal to see it working on localhost:3000  and if you have problems check your code against mine:
297 | 
298 | ```
299 | import React, { Component } from 'react';
300 | import './App.css';
301 | 
302 | class App extends Component {
303 |     constructor(props){
304 |         super(props)
305 | 
306 |         this.createVisualization = this.createVisualization.bind(this)
307 |     }
308 | 
309 |     componentDidMount(){
310 |         this.createVisualization()
311 |     }
312 | 
313 |     createVisualization(){
314 |         let context = new AudioContext();
315 |         let analyser = context.createAnalyser();
316 |         let canvas = this.refs.analyzerCanvas;
317 |         let ctx = canvas.getContext('2d');
318 |         let audio = this.refs.audio;
319 |         audio.crossOrigin = "anonymous";
320 |         let audioSrc = context.createMediaElementSource(audio);
321 |         audioSrc.connect(analyser);
322 |         audioSrc.connect(context.destination);
323 |         analyser.connect(context.destination);
324 | 
325 |         function renderFrame(){
326 |             let freqData = new Uint8Array(analyser.frequencyBinCount)
327 |             requestAnimationFrame(renderFrame)
328 |             analyser.getByteFrequencyData(freqData)
329 |             ctx.clearRect(0, 0, canvas.width, canvas.height)
330 |             console.log(freqData)
331 |             ctx.fillStyle = '#9933ff';
332 |             let bars = 100;
333 |             for (var i = 0; i < bars; i++) {
334 |                 let bar_x = i * 3;
335 |                 let bar_width = 2;
336 |                 let bar_height = -(freqData[i] / 2);
337 |                 ctx.fillRect(bar_x, canvas.height, bar_width, bar_height)
338 |             }
339 |         };
340 |         renderFrame()
341 |     }
342 | 
343 |     render() {
344 |         return (
345 |             <div className="App">
346 |                 <h2>Sublime - 40oz to Freedom</h2>
347 |                 <div id="mp3_player">
348 |                     <div id="audio_box">
349 |                         <audio
350 |                             ref="audio"
351 |                             autoPlay={true}
352 |                             controls={true}
353 |                             //this is the link to my song url feel free to use it or replace it with your own
354 |                             src={"https://p.scdn.co/mp3-preview/e4a8f30ca62b4d2a129cc4df76de66f43e12fa3f?cid=null"}
355 |                             >
356 |                             </audio>
357 |                         </div>
358 |                         <canvas
359 |                             ref="analyzerCanvas"
360 |                             id="analyzer"
361 |                             >
362 |                             </canvas>
363 |                         </div>
364 |                     </div>
365 |                 );
366 |             }
367 |         }
368 | 
369 |         export default App;
370 | ```
371 | 


--------------------------------------------------------------------------------
/audio-visuals/.gitignore:
--------------------------------------------------------------------------------
 1 | # See https://help.github.com/ignore-files/ for more about ignoring files.
 2 | 
 3 | # dependencies
 4 | /node_modules
 5 | 
 6 | # testing
 7 | /coverage
 8 | 
 9 | # production
10 | /build
11 | 
12 | # misc
13 | .DS_Store
14 | .env
15 | npm-debug.log*
16 | yarn-debug.log*
17 | yarn-error.log*
18 | 
19 | 


--------------------------------------------------------------------------------
/audio-visuals/README.md:
--------------------------------------------------------------------------------
   1 | This project was bootstrapped with [Create React App](https://github.com/facebookincubator/create-react-app).
   2 | 
   3 | Below you will find some information on how to perform common tasks.<br>
   4 | You can find the most recent version of this guide [here](https://github.com/facebookincubator/create-react-app/blob/master/packages/react-scripts/template/README.md).
   5 | 
   6 | ## Table of Contents
   7 | 
   8 | - [Updating to New Releases](#updating-to-new-releases)
   9 | - [Sending Feedback](#sending-feedback)
  10 | - [Folder Structure](#folder-structure)
  11 | - [Available Scripts](#available-scripts)
  12 |   - [npm start](#npm-start)
  13 |   - [npm test](#npm-test)
  14 |   - [npm run build](#npm-run-build)
  15 |   - [npm run eject](#npm-run-eject)
  16 | - [Supported Language Features and Polyfills](#supported-language-features-and-polyfills)
  17 | - [Syntax Highlighting in the Editor](#syntax-highlighting-in-the-editor)
  18 | - [Displaying Lint Output in the Editor](#displaying-lint-output-in-the-editor)
  19 | - [Debugging in the Editor](#debugging-in-the-editor)
  20 | - [Changing the Page `<title>`](#changing-the-page-title)
  21 | - [Installing a Dependency](#installing-a-dependency)
  22 | - [Importing a Component](#importing-a-component)
  23 | - [Adding a Stylesheet](#adding-a-stylesheet)
  24 | - [Post-Processing CSS](#post-processing-css)
  25 | - [Adding a CSS Preprocessor (Sass, Less etc.)](#adding-a-css-preprocessor-sass-less-etc)
  26 | - [Adding Images and Fonts](#adding-images-and-fonts)
  27 | - [Using the `public` Folder](#using-the-public-folder)
  28 |   - [Changing the HTML](#changing-the-html)
  29 |   - [Adding Assets Outside of the Module System](#adding-assets-outside-of-the-module-system)
  30 |   - [When to Use the `public` Folder](#when-to-use-the-public-folder)
  31 | - [Using Global Variables](#using-global-variables)
  32 | - [Adding Bootstrap](#adding-bootstrap)
  33 |   - [Using a Custom Theme](#using-a-custom-theme)
  34 | - [Adding Flow](#adding-flow)
  35 | - [Adding Custom Environment Variables](#adding-custom-environment-variables)
  36 |   - [Referencing Environment Variables in the HTML](#referencing-environment-variables-in-the-html)
  37 |   - [Adding Temporary Environment Variables In Your Shell](#adding-temporary-environment-variables-in-your-shell)
  38 |   - [Adding Development Environment Variables In `.env`](#adding-development-environment-variables-in-env)
  39 | - [Can I Use Decorators?](#can-i-use-decorators)
  40 | - [Integrating with an API Backend](#integrating-with-an-api-backend)
  41 |   - [Node](#node)
  42 |   - [Ruby on Rails](#ruby-on-rails)
  43 | - [Proxying API Requests in Development](#proxying-api-requests-in-development)
  44 | - [Using HTTPS in Development](#using-https-in-development)
  45 | - [Generating Dynamic `<meta>` Tags on the Server](#generating-dynamic-meta-tags-on-the-server)
  46 | - [Pre-Rendering into Static HTML Files](#pre-rendering-into-static-html-files)
  47 | - [Injecting Data from the Server into the Page](#injecting-data-from-the-server-into-the-page)
  48 | - [Running Tests](#running-tests)
  49 |   - [Filename Conventions](#filename-conventions)
  50 |   - [Command Line Interface](#command-line-interface)
  51 |   - [Version Control Integration](#version-control-integration)
  52 |   - [Writing Tests](#writing-tests)
  53 |   - [Testing Components](#testing-components)
  54 |   - [Using Third Party Assertion Libraries](#using-third-party-assertion-libraries)
  55 |   - [Initializing Test Environment](#initializing-test-environment)
  56 |   - [Focusing and Excluding Tests](#focusing-and-excluding-tests)
  57 |   - [Coverage Reporting](#coverage-reporting)
  58 |   - [Continuous Integration](#continuous-integration)
  59 |   - [Disabling jsdom](#disabling-jsdom)
  60 |   - [Snapshot Testing](#snapshot-testing)
  61 |   - [Editor Integration](#editor-integration)
  62 | - [Developing Components in Isolation](#developing-components-in-isolation)
  63 | - [Making a Progressive Web App](#making-a-progressive-web-app)
  64 | - [Deployment](#deployment)
  65 |   - [Static Server](#static-server)
  66 |   - [Other Solutions](#other-solutions)
  67 |   - [Serving Apps with Client-Side Routing](#serving-apps-with-client-side-routing)
  68 |   - [Building for Relative Paths](#building-for-relative-paths)
  69 |   - [Azure](#azure)
  70 |   - [Firebase](#firebase)
  71 |   - [GitHub Pages](#github-pages)
  72 |   - [Heroku](#heroku)
  73 |   - [Modulus](#modulus)
  74 |   - [Netlify](#netlify)
  75 |   - [Now](#now)
  76 |   - [S3 and CloudFront](#s3-and-cloudfront)
  77 |   - [Surge](#surge)
  78 | - [Advanced Configuration](#advanced-configuration)
  79 | - [Troubleshooting](#troubleshooting)
  80 |   - [`npm start` doesn’t detect changes](#npm-start-doesnt-detect-changes)
  81 |   - [`npm test` hangs on macOS Sierra](#npm-test-hangs-on-macos-sierra)
  82 |   - [`npm run build` silently fails](#npm-run-build-silently-fails)
  83 |   - [`npm run build` fails on Heroku](#npm-run-build-fails-on-heroku)
  84 | - [Something Missing?](#something-missing)
  85 | 
  86 | ## Updating to New Releases
  87 | 
  88 | Create React App is divided into two packages:
  89 | 
  90 | * `create-react-app` is a global command-line utility that you use to create new projects.
  91 | * `react-scripts` is a development dependency in the generated projects (including this one).
  92 | 
  93 | You almost never need to update `create-react-app` itself: it delegates all the setup to `react-scripts`.
  94 | 
  95 | When you run `create-react-app`, it always creates the project with the latest version of `react-scripts` so you’ll get all the new features and improvements in newly created apps automatically.
  96 | 
  97 | To update an existing project to a new version of `react-scripts`, [open the changelog](https://github.com/facebookincubator/create-react-app/blob/master/CHANGELOG.md), find the version you’re currently on (check `package.json` in this folder if you’re not sure), and apply the migration instructions for the newer versions.
  98 | 
  99 | In most cases bumping the `react-scripts` version in `package.json` and running `npm install` in this folder should be enough, but it’s good to consult the [changelog](https://github.com/facebookincubator/create-react-app/blob/master/CHANGELOG.md) for potential breaking changes.
 100 | 
 101 | We commit to keeping the breaking changes minimal so you can upgrade `react-scripts` painlessly.
 102 | 
 103 | ## Sending Feedback
 104 | 
 105 | We are always open to [your feedback](https://github.com/facebookincubator/create-react-app/issues).
 106 | 
 107 | ## Folder Structure
 108 | 
 109 | After creation, your project should look like this:
 110 | 
 111 | ```
 112 | my-app/
 113 |   README.md
 114 |   node_modules/
 115 |   package.json
 116 |   public/
 117 |     index.html
 118 |     favicon.ico
 119 |   src/
 120 |     App.css
 121 |     App.js
 122 |     App.test.js
 123 |     index.css
 124 |     index.js
 125 |     logo.svg
 126 | ```
 127 | 
 128 | For the project to build, **these files must exist with exact filenames**:
 129 | 
 130 | * `public/index.html` is the page template;
 131 | * `src/index.js` is the JavaScript entry point.
 132 | 
 133 | You can delete or rename the other files.
 134 | 
 135 | You may create subdirectories inside `src`. For faster rebuilds, only files inside `src` are processed by Webpack.<br>
 136 | You need to **put any JS and CSS files inside `src`**, or Webpack won’t see them.
 137 | 
 138 | Only files inside `public` can be used from `public/index.html`.<br>
 139 | Read instructions below for using assets from JavaScript and HTML.
 140 | 
 141 | You can, however, create more top-level directories.<br>
 142 | They will not be included in the production build so you can use them for things like documentation.
 143 | 
 144 | ## Available Scripts
 145 | 
 146 | In the project directory, you can run:
 147 | 
 148 | ### `npm start`
 149 | 
 150 | Runs the app in the development mode.<br>
 151 | Open [http://localhost:3000](http://localhost:3000) to view it in the browser.
 152 | 
 153 | The page will reload if you make edits.<br>
 154 | You will also see any lint errors in the console.
 155 | 
 156 | ### `npm test`
 157 | 
 158 | Launches the test runner in the interactive watch mode.<br>
 159 | See the section about [running tests](#running-tests) for more information.
 160 | 
 161 | ### `npm run build`
 162 | 
 163 | Builds the app for production to the `build` folder.<br>
 164 | It correctly bundles React in production mode and optimizes the build for the best performance.
 165 | 
 166 | The build is minified and the filenames include the hashes.<br>
 167 | Your app is ready to be deployed!
 168 | 
 169 | See the section about [deployment](#deployment) for more information.
 170 | 
 171 | ### `npm run eject`
 172 | 
 173 | **Note: this is a one-way operation. Once you `eject`, you can’t go back!**
 174 | 
 175 | If you aren’t satisfied with the build tool and configuration choices, you can `eject` at any time. This command will remove the single build dependency from your project.
 176 | 
 177 | Instead, it will copy all the configuration files and the transitive dependencies (Webpack, Babel, ESLint, etc) right into your project so you have full control over them. All of the commands except `eject` will still work, but they will point to the copied scripts so you can tweak them. At this point you’re on your own.
 178 | 
 179 | You don’t have to ever use `eject`. The curated feature set is suitable for small and middle deployments, and you shouldn’t feel obligated to use this feature. However we understand that this tool wouldn’t be useful if you couldn’t customize it when you are ready for it.
 180 | 
 181 | ## Supported Language Features and Polyfills
 182 | 
 183 | This project supports a superset of the latest JavaScript standard.<br>
 184 | In addition to [ES6](https://github.com/lukehoban/es6features) syntax features, it also supports:
 185 | 
 186 | * [Exponentiation Operator](https://github.com/rwaldron/exponentiation-operator) (ES2016).
 187 | * [Async/await](https://github.com/tc39/ecmascript-asyncawait) (ES2017).
 188 | * [Object Rest/Spread Properties](https://github.com/sebmarkbage/ecmascript-rest-spread) (stage 3 proposal).
 189 | * [Class Fields and Static Properties](https://github.com/tc39/proposal-class-public-fields) (stage 2 proposal).
 190 | * [JSX](https://facebook.github.io/react/docs/introducing-jsx.html) and [Flow](https://flowtype.org/) syntax.
 191 | 
 192 | Learn more about [different proposal stages](https://babeljs.io/docs/plugins/#presets-stage-x-experimental-presets-).
 193 | 
 194 | While we recommend to use experimental proposals with some caution, Facebook heavily uses these features in the product code, so we intend to provide [codemods](https://medium.com/@cpojer/effective-javascript-codemods-5a6686bb46fb) if any of these proposals change in the future.
 195 | 
 196 | Note that **the project only includes a few ES6 [polyfills](https://en.wikipedia.org/wiki/Polyfill)**:
 197 | 
 198 | * [`Object.assign()`](https://developer.mozilla.org/en/docs/Web/JavaScript/Reference/Global_Objects/Object/assign) via [`object-assign`](https://github.com/sindresorhus/object-assign).
 199 | * [`Promise`](https://developer.mozilla.org/en-US/docs/Web/JavaScript/Reference/Global_Objects/Promise) via [`promise`](https://github.com/then/promise).
 200 | * [`fetch()`](https://developer.mozilla.org/en/docs/Web/API/Fetch_API) via [`whatwg-fetch`](https://github.com/github/fetch).
 201 | 
 202 | If you use any other ES6+ features that need **runtime support** (such as `Array.from()` or `Symbol`), make sure you are including the appropriate polyfills manually, or that the browsers you are targeting already support them.
 203 | 
 204 | ## Syntax Highlighting in the Editor
 205 | 
 206 | To configure the syntax highlighting in your favorite text editor, head to the [relevant Babel documentation page](https://babeljs.io/docs/editors) and follow the instructions. Some of the most popular editors are covered.
 207 | 
 208 | ## Displaying Lint Output in the Editor
 209 | 
 210 | >Note: this feature is available with `react-scripts@0.2.0` and higher.
 211 | 
 212 | Some editors, including Sublime Text, Atom, and Visual Studio Code, provide plugins for ESLint.
 213 | 
 214 | They are not required for linting. You should see the linter output right in your terminal as well as the browser console. However, if you prefer the lint results to appear right in your editor, there are some extra steps you can do.
 215 | 
 216 | You would need to install an ESLint plugin for your editor first.
 217 | 
 218 | >**A note for Atom `linter-eslint` users**
 219 | 
 220 | >If you are using the Atom `linter-eslint` plugin, make sure that **Use global ESLint installation** option is checked:
 221 | 
 222 | ><img src="http://i.imgur.com/yVNNHJM.png" width="300">
 223 | 
 224 | 
 225 | >**For Visual Studio Code users**
 226 | 
 227 | >VS Code ESLint plugin automatically detects Create React App's configuration file. So you do not need to create `eslintrc.json` at the root directory, except when you want to add your own rules. In that case, you should include CRA's config by adding this line:
 228 | 
 229 | >```js
 230 | {
 231 |   // ...
 232 |   "extends": "react-app"
 233 | }
 234 | ```
 235 | 
 236 | Then add this block to the `package.json` file of your project:
 237 | 
 238 | ```js
 239 | {
 240 |   // ...
 241 |   "eslintConfig": {
 242 |     "extends": "react-app"
 243 |   }
 244 | }
 245 | ```
 246 | 
 247 | Finally, you will need to install some packages *globally*:
 248 | 
 249 | ```sh
 250 | npm install -g eslint-config-react-app@0.3.0 eslint@3.8.1 babel-eslint@7.0.0 eslint-plugin-react@6.4.1 eslint-plugin-import@2.0.1 eslint-plugin-jsx-a11y@4.0.0 eslint-plugin-flowtype@2.21.0
 251 | ```
 252 | 
 253 | We recognize that this is suboptimal, but it is currently required due to the way we hide the ESLint dependency. The ESLint team is already [working on a solution to this](https://github.com/eslint/eslint/issues/3458) so this may become unnecessary in a couple of months.
 254 | 
 255 | ## Debugging in the Editor
 256 | 
 257 | **This feature is currently only supported by [Visual Studio Code](https://code.visualstudio.com) editor.**
 258 | 
 259 | Visual Studio Code supports live-editing and debugging out of the box with Create React App. This enables you as a developer to write and debug your React code without leaving the editor, and most importantly it enables you to have a continuous development workflow, where context switching is minimal, as you don’t have to switch between tools.
 260 | 
 261 | You would need to have the latest version of [VS Code](https://code.visualstudio.com) and VS Code [Chrome Debugger Extension](https://marketplace.visualstudio.com/items?itemName=msjsdiag.debugger-for-chrome) installed.
 262 | 
 263 | Then add the block below to your `launch.json` file and put it inside the `.vscode` folder in your app’s root directory.
 264 | 
 265 | ```json
 266 | {
 267 |   "version": "0.2.0",
 268 |   "configurations": [{
 269 |     "name": "Chrome",
 270 |     "type": "chrome",
 271 |     "request": "launch",
 272 |     "url": "http://localhost:3000",
 273 |     "webRoot": "${workspaceRoot}/src",
 274 |     "userDataDir": "${workspaceRoot}/.vscode/chrome",
 275 |     "sourceMapPathOverrides": {
 276 |       "webpack:///src/*": "${webRoot}/*"
 277 |     }
 278 |   }]
 279 | }
 280 | ```
 281 | 
 282 | Start your app by running `npm start`, and start debugging in VS Code by pressing `F5` or by clicking the green debug icon. You can now write code, set breakpoints, make changes to the code, and debug your newly modified code—all from your editor.
 283 | 
 284 | ## Changing the Page `<title>`
 285 | 
 286 | You can find the source HTML file in the `public` folder of the generated project. You may edit the `<title>` tag in it to change the title from “React App” to anything else.
 287 | 
 288 | Note that normally you wouldn’t edit files in the `public` folder very often. For example, [adding a stylesheet](#adding-a-stylesheet) is done without touching the HTML.
 289 | 
 290 | If you need to dynamically update the page title based on the content, you can use the browser [`document.title`](https://developer.mozilla.org/en-US/docs/Web/API/Document/title) API. For more complex scenarios when you want to change the title from React components, you can use [React Helmet](https://github.com/nfl/react-helmet), a third party library.
 291 | 
 292 | If you use a custom server for your app in production and want to modify the title before it gets sent to the browser, you can follow advice in [this section](#generating-dynamic-meta-tags-on-the-server). Alternatively, you can pre-build each page as a static HTML file which then loads the JavaScript bundle, which is covered [here](#pre-rendering-into-static-html-files).
 293 | 
 294 | ## Installing a Dependency
 295 | 
 296 | The generated project includes React and ReactDOM as dependencies. It also includes a set of scripts used by Create React App as a development dependency. You may install other dependencies (for example, React Router) with `npm`:
 297 | 
 298 | ```
 299 | npm install --save <library-name>
 300 | ```
 301 | 
 302 | ## Importing a Component
 303 | 
 304 | This project setup supports ES6 modules thanks to Babel.<br>
 305 | While you can still use `require()` and `module.exports`, we encourage you to use [`import` and `export`](http://exploringjs.com/es6/ch_modules.html) instead.
 306 | 
 307 | For example:
 308 | 
 309 | ### `Button.js`
 310 | 
 311 | ```js
 312 | import React, { Component } from 'react';
 313 | 
 314 | class Button extends Component {
 315 |   render() {
 316 |     // ...
 317 |   }
 318 | }
 319 | 
 320 | export default Button; // Don’t forget to use export default!
 321 | ```
 322 | 
 323 | ### `DangerButton.js`
 324 | 
 325 | 
 326 | ```js
 327 | import React, { Component } from 'react';
 328 | import Button from './Button'; // Import a component from another file
 329 | 
 330 | class DangerButton extends Component {
 331 |   render() {
 332 |     return <Button color="red" />;
 333 |   }
 334 | }
 335 | 
 336 | export default DangerButton;
 337 | ```
 338 | 
 339 | Be aware of the [difference between default and named exports](http://stackoverflow.com/questions/36795819/react-native-es-6-when-should-i-use-curly-braces-for-import/36796281#36796281). It is a common source of mistakes.
 340 | 
 341 | We suggest that you stick to using default imports and exports when a module only exports a single thing (for example, a component). That’s what you get when you use `export default Button` and `import Button from './Button'`.
 342 | 
 343 | Named exports are useful for utility modules that export several functions. A module may have at most one default export and as many named exports as you like.
 344 | 
 345 | Learn more about ES6 modules:
 346 | 
 347 | * [When to use the curly braces?](http://stackoverflow.com/questions/36795819/react-native-es-6-when-should-i-use-curly-braces-for-import/36796281#36796281)
 348 | * [Exploring ES6: Modules](http://exploringjs.com/es6/ch_modules.html)
 349 | * [Understanding ES6: Modules](https://leanpub.com/understandinges6/read#leanpub-auto-encapsulating-code-with-modules)
 350 | 
 351 | ## Adding a Stylesheet
 352 | 
 353 | This project setup uses [Webpack](https://webpack.github.io/) for handling all assets. Webpack offers a custom way of “extending” the concept of `import` beyond JavaScript. To express that a JavaScript file depends on a CSS file, you need to **import the CSS from the JavaScript file**:
 354 | 
 355 | ### `Button.css`
 356 | 
 357 | ```css
 358 | .Button {
 359 |   padding: 20px;
 360 | }
 361 | ```
 362 | 
 363 | ### `Button.js`
 364 | 
 365 | ```js
 366 | import React, { Component } from 'react';
 367 | import './Button.css'; // Tell Webpack that Button.js uses these styles
 368 | 
 369 | class Button extends Component {
 370 |   render() {
 371 |     // You can use them as regular CSS styles
 372 |     return <div className="Button" />;
 373 |   }
 374 | }
 375 | ```
 376 | 
 377 | **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.
 378 | 
 379 | 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.
 380 | 
 381 | 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.
 382 | 
 383 | ## Post-Processing CSS
 384 | 
 385 | 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.
 386 | 
 387 | For example, this:
 388 | 
 389 | ```css
 390 | .App {
 391 |   display: flex;
 392 |   flex-direction: row;
 393 |   align-items: center;
 394 | }
 395 | ```
 396 | 
 397 | becomes this:
 398 | 
 399 | ```css
 400 | .App {
 401 |   display: -webkit-box;
 402 |   display: -ms-flexbox;
 403 |   display: flex;
 404 |   -webkit-box-orient: horizontal;
 405 |   -webkit-box-direction: normal;
 406 |       -ms-flex-direction: row;
 407 |           flex-direction: row;
 408 |   -webkit-box-align: center;
 409 |       -ms-flex-align: center;
 410 |           align-items: center;
 411 | }
 412 | ```
 413 | 
 414 | If you need to disable autoprefixing for some reason, [follow this section](https://github.com/postcss/autoprefixer#disabling).
 415 | 
 416 | ## Adding a CSS Preprocessor (Sass, Less etc.)
 417 | 
 418 | Generally, we recommend that you don’t reuse the same CSS classes across different components. For example, instead of using a `.Button` CSS class in `<AcceptButton>` and `<RejectButton>` components, we recommend creating a `<Button>` component with its own `.Button` styles, that both `<AcceptButton>` and `<RejectButton>` can render (but [not inherit](https://facebook.github.io/react/docs/composition-vs-inheritance.html)).
 419 | 
 420 | Following this rule often makes CSS preprocessors less useful, as features like mixins and nesting are replaced by component composition. You can, however, integrate a CSS preprocessor if you find it valuable. In this walkthrough, we will be using Sass, but you can also use Less, or another alternative.
 421 | 
 422 | First, let’s install the command-line interface for Sass:
 423 | 
 424 | ```
 425 | npm install node-sass --save-dev
 426 | ```
 427 | 
 428 | Then in `package.json`, add the following lines to `scripts`:
 429 | 
 430 | ```diff
 431 |    "scripts": {
 432 | +    "build-css": "node-sass src/ -o src/",
 433 | +    "watch-css": "npm run build-css && node-sass src/ -o src/ --watch --recursive",
 434 |      "start": "react-scripts start",
 435 |      "build": "react-scripts build",
 436 |      "test": "react-scripts test --env=jsdom",
 437 | ```
 438 | 
 439 | >Note: To use a different preprocessor, replace `build-css` and `watch-css` commands according to your preprocessor’s documentation.
 440 | 
 441 | Now you can rename `src/App.css` to `src/App.scss` and run `npm run watch-css`. The watcher will find every Sass file in `src` subdirectories, and create a corresponding CSS file next to it, in our case overwriting `src/App.css`. Since `src/App.js` still imports `src/App.css`, the styles become a part of your application. You can now edit `src/App.scss`, and `src/App.css` will be regenerated.
 442 | 
 443 | To share variables between Sass files, you can use Sass imports. For example, `src/App.scss` and other component style files could include `@import "./shared.scss";` with variable definitions.
 444 | 
 445 | At this point you might want to remove all CSS files from the source control, and add `src/**/*.css` to your `.gitignore` file. It is generally a good practice to keep the build products outside of the source control.
 446 | 
 447 | As a final step, you may find it convenient to run `watch-css` automatically with `npm start`, and run `build-css` as a part of `npm run build`. You can use the `&&` operator to execute two scripts sequentially. However, there is no cross-platform way to run two scripts in parallel, so we will install a package for this:
 448 | 
 449 | ```
 450 | npm install --save-dev npm-run-all
 451 | ```
 452 | 
 453 | Then we can change `start` and `build` scripts to include the CSS preprocessor commands:
 454 | 
 455 | ```diff
 456 |    "scripts": {
 457 |      "build-css": "node-sass src/ -o src/",
 458 |      "watch-css": "npm run build-css && node-sass src/ -o src/ --watch --recursive",
 459 | -    "start": "react-scripts start",
 460 | -    "build": "react-scripts build",
 461 | +    "start-js": "react-scripts start",
 462 | +    "start": "npm-run-all -p watch-css start-js",
 463 | +    "build": "npm run build-css && react-scripts build",
 464 |      "test": "react-scripts test --env=jsdom",
 465 |      "eject": "react-scripts eject"
 466 |    }
 467 | ```
 468 | 
 469 | Now running `npm start` and `npm run build` also builds Sass files. Note that `node-sass` seems to have an [issue recognizing newly created files on some systems](https://github.com/sass/node-sass/issues/1891) so you might need to restart the watcher when you create a file until it’s resolved.
 470 | 
 471 | ## Adding Images and Fonts
 472 | 
 473 | With Webpack, using static assets like images and fonts works similarly to CSS.
 474 | 
 475 | 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.
 476 | 
 477 | Here is an example:
 478 | 
 479 | ```js
 480 | import React from 'react';
 481 | import logo from './logo.png'; // Tell Webpack this JS file uses this image
 482 | 
 483 | console.log(logo); // /logo.84287d09.png
 484 | 
 485 | function Header() {
 486 |   // Import result is the URL of your image
 487 |   return <img src={logo} alt="Logo" />;
 488 | }
 489 | 
 490 | export default Header;
 491 | ```
 492 | 
 493 | This ensures that when the project is built, Webpack will correctly move the images into the build folder, and provide us with correct paths.
 494 | 
 495 | This works in CSS too:
 496 | 
 497 | ```css
 498 | .Logo {
 499 |   background-image: url(./logo.png);
 500 | }
 501 | ```
 502 | 
 503 | 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.
 504 | 
 505 | Please be advised that this is also a custom feature of Webpack.
 506 | 
 507 | **It is not required for React** but many people enjoy it (and React Native uses a similar mechanism for images).<br>
 508 | An alternative way of handling static assets is described in the next section.
 509 | 
 510 | ## Using the `public` Folder
 511 | 
 512 | >Note: this feature is available with `react-scripts@0.5.0` and higher.
 513 | 
 514 | ### Changing the HTML
 515 | 
 516 | The `public` folder contains the HTML file so you can tweak it, for example, to [set the page title](#changing-the-page-title).
 517 | The `<script>` tag with the compiled code will be added to it automatically during the build process.
 518 | 
 519 | ### Adding Assets Outside of the Module System
 520 | 
 521 | You can also add other assets to the `public` folder.
 522 | 
 523 | Note that we normally encourage you to `import` assets in JavaScript files instead.
 524 | For example, see the sections on [adding a stylesheet](#adding-a-stylesheet) and [adding images and fonts](#adding-images-and-fonts).
 525 | This mechanism provides a number of benefits:
 526 | 
 527 | * Scripts and stylesheets get minified and bundled together to avoid extra network requests.
 528 | * Missing files cause compilation errors instead of 404 errors for your users.
 529 | * Result filenames include content hashes so you don’t need to worry about browsers caching their old versions.
 530 | 
 531 | However there is an **escape hatch** that you can use to add an asset outside of the module system.
 532 | 
 533 | If you put a file into the `public` folder, it will **not** be processed by Webpack. Instead it will be copied into the build folder untouched.   To reference assets in the `public` folder, you need to use a special variable called `PUBLIC_URL`.
 534 | 
 535 | Inside `index.html`, you can use it like this:
 536 | 
 537 | ```html
 538 | <link rel="shortcut icon" href="%PUBLIC_URL%/favicon.ico">
 539 | ```
 540 | 
 541 | Only files inside the `public` folder will be accessible by `%PUBLIC_URL%` prefix. If you need to use a file from `src` or `node_modules`, you’ll have to copy it there to explicitly specify your intention to make this file a part of the build.
 542 | 
 543 | When you run `npm run build`, Create React App will substitute `%PUBLIC_URL%` with a correct absolute path so your project works even if you use client-side routing or host it at a non-root URL.
 544 | 
 545 | In JavaScript code, you can use `process.env.PUBLIC_URL` for similar purposes:
 546 | 
 547 | ```js
 548 | render() {
 549 |   // Note: this is an escape hatch and should be used sparingly!
 550 |   // Normally we recommend using `import` for getting asset URLs
 551 |   // as described in “Adding Images and Fonts” above this section.
 552 |   return <img src={process.env.PUBLIC_URL + '/img/logo.png'} />;
 553 | }
 554 | ```
 555 | 
 556 | Keep in mind the downsides of this approach:
 557 | 
 558 | * None of the files in `public` folder get post-processed or minified.
 559 | * Missing files will not be called at compilation time, and will cause 404 errors for your users.
 560 | * Result filenames won’t include content hashes so you’ll need to add query arguments or rename them every time they change.
 561 | 
 562 | ### When to Use the `public` Folder
 563 | 
 564 | Normally we recommend importing [stylesheets](#adding-a-stylesheet), [images, and fonts](#adding-images-and-fonts) from JavaScript.
 565 | The `public` folder is useful as a workaround for a number of less common cases:
 566 | 
 567 | * You need a file with a specific name in the build output, such as [`manifest.webmanifest`](https://developer.mozilla.org/en-US/docs/Web/Manifest).
 568 | * You have thousands of images and need to dynamically reference their paths.
 569 | * You want to include a small script like [`pace.js`](http://github.hubspot.com/pace/docs/welcome/) outside of the bundled code.
 570 | * Some library may be incompatible with Webpack and you have no other option but to include it as a `<script>` tag.
 571 | 
 572 | Note that if you add a `<script>` that declares global variables, you also need to read the next section on using them.
 573 | 
 574 | ## Using Global Variables
 575 | 
 576 | When you include a script in the HTML file that defines global variables and try to use one of these variables in the code, the linter will complain because it cannot see the definition of the variable.
 577 | 
 578 | You can avoid this by reading the global variable explicitly from the `window` object, for example:
 579 | 
 580 | ```js
 581 | const $ = window.$;
 582 | ```
 583 | 
 584 | This makes it obvious you are using a global variable intentionally rather than because of a typo.
 585 | 
 586 | Alternatively, you can force the linter to ignore any line by adding `// eslint-disable-line` after it.
 587 | 
 588 | ## Adding Bootstrap
 589 | 
 590 | 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:
 591 | 
 592 | Install React Bootstrap and Bootstrap from npm. React Bootstrap does not include Bootstrap CSS so this needs to be installed as well:
 593 | 
 594 | ```
 595 | npm install react-bootstrap --save
 596 | npm install bootstrap@3 --save
 597 | ```
 598 | 
 599 | Import Bootstrap CSS and optionally Bootstrap theme CSS in the beginning of your ```src/index.js``` file:
 600 | 
 601 | ```js
 602 | import 'bootstrap/dist/css/bootstrap.css';
 603 | import 'bootstrap/dist/css/bootstrap-theme.css';
 604 | // Put any other imports below so that CSS from your
 605 | // components takes precedence over default styles.
 606 | ```
 607 | 
 608 | Import required React Bootstrap components within ```src/App.js``` file or your custom component files:
 609 | 
 610 | ```js
 611 | import { Navbar, Jumbotron, Button } from 'react-bootstrap';
 612 | ```
 613 | 
 614 | 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.
 615 | 
 616 | ### Using a Custom Theme
 617 | 
 618 | Sometimes you might need to tweak the visual styles of Bootstrap (or equivalent package).<br>
 619 | We suggest the following approach:
 620 | 
 621 | * Create a new package that depends on the package you wish to customize, e.g. Bootstrap.
 622 | * Add the necessary build steps to tweak the theme, and publish your package on npm.
 623 | * Install your own theme npm package as a dependency of your app.
 624 | 
 625 | Here is an example of adding a [customized Bootstrap](https://medium.com/@tacomanator/customizing-create-react-app-aa9ffb88165) that follows these steps.
 626 | 
 627 | ## Adding Flow
 628 | 
 629 | Flow is a static type checker that helps you write code with fewer bugs. Check out this [introduction to using static types in JavaScript](https://medium.com/@preethikasireddy/why-use-static-types-in-javascript-part-1-8382da1e0adb) if you are new to this concept.
 630 | 
 631 | Recent versions of [Flow](http://flowtype.org/) work with Create React App projects out of the box.
 632 | 
 633 | To add Flow to a Create React App project, follow these steps:
 634 | 
 635 | 1. Run `npm install --save-dev flow-bin` (or `yarn add --dev flow-bin`).
 636 | 2. Add `"flow": "flow"` to the `scripts` section of your `package.json`.
 637 | 3. Run `npm run flow -- init` (or `yarn flow -- init`) to create a [`.flowconfig` file](https://flowtype.org/docs/advanced-configuration.html) in the root directory.
 638 | 4. Add `// @flow` to any files you want to type check (for example, to `src/App.js`).
 639 | 
 640 | Now you can run `npm run flow` (or `yarn flow`) to check the files for type errors.
 641 | You can optionally use an IDE like [Nuclide](https://nuclide.io/docs/languages/flow/) for a better integrated experience.
 642 | In the future we plan to integrate it into Create React App even more closely.
 643 | 
 644 | To learn more about Flow, check out [its documentation](https://flowtype.org/).
 645 | 
 646 | ## Adding Custom Environment Variables
 647 | 
 648 | >Note: this feature is available with `react-scripts@0.2.3` and higher.
 649 | 
 650 | Your project can consume variables declared in your environment as if they were declared locally in your JS files. By
 651 | default you will have `NODE_ENV` defined for you, and any other environment variables starting with
 652 | `REACT_APP_`.
 653 | 
 654 | **The environment variables are embedded during the build time**. Since Create React App produces a static HTML/CSS/JS bundle, it can’t possibly read them at runtime. To read them at runtime, you would need to load HTML into memory on the server and replace placeholders in runtime, just like [described here](#injecting-data-from-the-server-into-the-page). Alternatively you can rebuild the app on the server anytime you change them.
 655 | 
 656 | >Note: You must create custom environment variables beginning with `REACT_APP_`. Any other variables except `NODE_ENV` will be ignored to avoid accidentally [exposing a private key on the machine that could have the same name](https://github.com/facebookincubator/create-react-app/issues/865#issuecomment-252199527). Changing any environment variables will require you to restart the development server if it is running.
 657 | 
 658 | These environment variables will be defined for you on `process.env`. For example, having an environment
 659 | variable named `REACT_APP_SECRET_CODE` will be exposed in your JS as `process.env.REACT_APP_SECRET_CODE`.
 660 | 
 661 | There is also a special built-in environment variable called `NODE_ENV`. You can read it from `process.env.NODE_ENV`. When you run `npm start`, it is always equal to `'development'`, when you run `npm test` it is always equal to `'test'`, and when you run `npm run build` to make a production bundle, it is always equal to `'production'`. **You cannot override `NODE_ENV` manually.** This prevents developers from accidentally deploying a slow development build to production.
 662 | 
 663 | These environment variables can be useful for displaying information conditionally based on where the project is
 664 | deployed or consuming sensitive data that lives outside of version control.
 665 | 
 666 | First, you need to have environment variables defined. For example, let’s say you wanted to consume a secret defined
 667 | in the environment inside a `<form>`:
 668 | 
 669 | ```jsx
 670 | render() {
 671 |   return (
 672 |     <div>
 673 |       <small>You are running this application in <b>{process.env.NODE_ENV}</b> mode.</small>
 674 |       <form>
 675 |         <input type="hidden" defaultValue={process.env.REACT_APP_SECRET_CODE} />
 676 |       </form>
 677 |     </div>
 678 |   );
 679 | }
 680 | ```
 681 | 
 682 | During the build, `process.env.REACT_APP_SECRET_CODE` will be replaced with the current value of the `REACT_APP_SECRET_CODE` environment variable. Remember that the `NODE_ENV` variable will be set for you automatically.
 683 | 
 684 | When you load the app in the browser and inspect the `<input>`, you will see its value set to `abcdef`, and the bold text will show the environment provided when using `npm start`:
 685 | 
 686 | ```html
 687 | <div>
 688 |   <small>You are running this application in <b>development</b> mode.</small>
 689 |   <form>
 690 |     <input type="hidden" value="abcdef" />
 691 |   </form>
 692 | </div>
 693 | ```
 694 | 
 695 | The above form is looking for a variable called `REACT_APP_SECRET_CODE` from the environment. In order to consume this
 696 | value, we need to have it defined in the environment. This can be done using two ways: either in your shell or in
 697 | a `.env` file. Both of these ways are described in the next few sections.
 698 | 
 699 | Having access to the `NODE_ENV` is also useful for performing actions conditionally:
 700 | 
 701 | ```js
 702 | if (process.env.NODE_ENV !== 'production') {
 703 |   analytics.disable();
 704 | }
 705 | ```
 706 | 
 707 | When you compile the app with `npm run build`, the minification step will strip out this condition, and the resulting bundle will be smaller.
 708 | 
 709 | ### Referencing Environment Variables in the HTML
 710 | 
 711 | >Note: this feature is available with `react-scripts@0.9.0` and higher.
 712 | 
 713 | You can also access the environment variables starting with `REACT_APP_` in the `public/index.html`. For example:
 714 | 
 715 | ```html
 716 | <title>%REACT_APP_WEBSITE_NAME%</title>
 717 | ```
 718 | 
 719 | Note that the caveats from the above section apply:
 720 | 
 721 | * Apart from a few built-in variables (`NODE_ENV` and `PUBLIC_URL`), variable names must start with `REACT_APP_` to work.
 722 | * The environment variables are injected at build time. If you need to inject them at runtime, [follow this approach instead](#generating-dynamic-meta-tags-on-the-server).
 723 | 
 724 | ### Adding Temporary Environment Variables In Your Shell
 725 | 
 726 | Defining environment variables can vary between OSes. It’s also important to know that this manner is temporary for the
 727 | life of the shell session.
 728 | 
 729 | #### Windows (cmd.exe)
 730 | 
 731 | ```cmd
 732 | set REACT_APP_SECRET_CODE=abcdef&&npm start
 733 | ```
 734 | 
 735 | (Note: the lack of whitespace is intentional.)
 736 | 
 737 | #### Linux, macOS (Bash)
 738 | 
 739 | ```bash
 740 | REACT_APP_SECRET_CODE=abcdef npm start
 741 | ```
 742 | 
 743 | ### Adding Development Environment Variables In `.env`
 744 | 
 745 | >Note: this feature is available with `react-scripts@0.5.0` and higher.
 746 | 
 747 | To define permanent environment variables, create a file called `.env` in the root of your project:
 748 | 
 749 | ```
 750 | REACT_APP_SECRET_CODE=abcdef
 751 | ```
 752 | 
 753 | These variables will act as the defaults if the machine does not explicitly set them.<br>
 754 | Please refer to the [dotenv documentation](https://github.com/motdotla/dotenv) for more details.
 755 | 
 756 | >Note: If you are defining environment variables for development, your CI and/or hosting platform will most likely need
 757 | these defined as well. Consult their documentation how to do this. For example, see the documentation for [Travis CI](https://docs.travis-ci.com/user/environment-variables/) or [Heroku](https://devcenter.heroku.com/articles/config-vars).
 758 | 
 759 | ## Can I Use Decorators?
 760 | 
 761 | Many popular libraries use [decorators](https://medium.com/google-developers/exploring-es7-decorators-76ecb65fb841) in their documentation.<br>
 762 | Create React App doesn’t support decorator syntax at the moment because:
 763 | 
 764 | * It is an experimental proposal and is subject to change.
 765 | * The current specification version is not officially supported by Babel.
 766 | * If the specification changes, we won’t be able to write a codemod because we don’t use them internally at Facebook.
 767 | 
 768 | However in many cases you can rewrite decorator-based code without decorators just as fine.<br>
 769 | Please refer to these two threads for reference:
 770 | 
 771 | * [#214](https://github.com/facebookincubator/create-react-app/issues/214)
 772 | * [#411](https://github.com/facebookincubator/create-react-app/issues/411)
 773 | 
 774 | Create React App will add decorator support when the specification advances to a stable stage.
 775 | 
 776 | ## Integrating with an API Backend
 777 | 
 778 | These tutorials will help you to integrate your app with an API backend running on another port,
 779 | using `fetch()` to access it.
 780 | 
 781 | ### Node
 782 | Check out [this tutorial](https://www.fullstackreact.com/articles/using-create-react-app-with-a-server/).
 783 | You can find the companion GitHub repository [here](https://github.com/fullstackreact/food-lookup-demo).
 784 | 
 785 | ### Ruby on Rails
 786 | 
 787 | Check out [this tutorial](https://www.fullstackreact.com/articles/how-to-get-create-react-app-to-work-with-your-rails-api/).
 788 | You can find the companion GitHub repository [here](https://github.com/fullstackreact/food-lookup-demo-rails).
 789 | 
 790 | ## Proxying API Requests in Development
 791 | 
 792 | >Note: this feature is available with `react-scripts@0.2.3` and higher.
 793 | 
 794 | People often serve the front-end React app from the same host and port as their backend implementation.<br>
 795 | For example, a production setup might look like this after the app is deployed:
 796 | 
 797 | ```
 798 | /             - static server returns index.html with React app
 799 | /todos        - static server returns index.html with React app
 800 | /api/todos    - server handles any /api/* requests using the backend implementation
 801 | ```
 802 | 
 803 | 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.
 804 | 
 805 | 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:
 806 | 
 807 | ```js
 808 |   "proxy": "http://localhost:4000",
 809 | ```
 810 | 
 811 | 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. The development server will only attempt to send requests without a `text/html` accept header to the proxy.
 812 | 
 813 | Conveniently, this avoids [CORS issues](http://stackoverflow.com/questions/21854516/understanding-ajax-cors-and-security-considerations) and error messages like this in development:
 814 | 
 815 | ```
 816 | 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.
 817 | ```
 818 | 
 819 | 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 without a `text/html` accept header will be redirected to the specified `proxy`.
 820 | 
 821 | The `proxy` option supports HTTP, HTTPS and WebSocket connections.<br>
 822 | If the `proxy` option is **not** flexible enough for you, alternatively you can:
 823 | 
 824 | * Enable CORS on your server ([here’s how to do it for Express](http://enable-cors.org/server_expressjs.html)).
 825 | * Use [environment variables](#adding-custom-environment-variables) to inject the right server host and port into your app.
 826 | 
 827 | ## Using HTTPS in Development
 828 | 
 829 | >Note: this feature is available with `react-scripts@0.4.0` and higher.
 830 | 
 831 | You may require the dev server to serve pages over HTTPS. One particular case where this could be useful is when using [the "proxy" feature](#proxying-api-requests-in-development) to proxy requests to an API server when that API server is itself serving HTTPS.
 832 | 
 833 | To do this, set the `HTTPS` environment variable to `true`, then start the dev server as usual with `npm start`:
 834 | 
 835 | #### Windows (cmd.exe)
 836 | 
 837 | ```cmd
 838 | set HTTPS=true&&npm start
 839 | ```
 840 | 
 841 | (Note: the lack of whitespace is intentional.)
 842 | 
 843 | #### Linux, macOS (Bash)
 844 | 
 845 | ```bash
 846 | HTTPS=true npm start
 847 | ```
 848 | 
 849 | Note that the server will use a self-signed certificate, so your web browser will almost definitely display a warning upon accessing the page.
 850 | 
 851 | ## Generating Dynamic `<meta>` Tags on the Server
 852 | 
 853 | Since Create React App doesn’t support server rendering, you might be wondering how to make `<meta>` tags dynamic and reflect the current URL. To solve this, we recommend to add placeholders into the HTML, like this:
 854 | 
 855 | ```html
 856 | <!doctype html>
 857 | <html lang="en">
 858 |   <head>
 859 |     <meta property="og:title" content="__OG_TITLE__">
 860 |     <meta property="og:description" content="__OG_DESCRIPTION__">
 861 | ```
 862 | 
 863 | Then, on the server, regardless of the backend you use, you can read `index.html` into memory and replace `__OG_TITLE__`, `__OG_DESCRIPTION__`, and any other placeholders with values depending on the current URL. Just make sure to sanitize and escape the interpolated values so that they are safe to embed into HTML!
 864 | 
 865 | If you use a Node server, you can even share the route matching logic between the client and the server. However duplicating it also works fine in simple cases.
 866 | 
 867 | ## Pre-Rendering into Static HTML Files
 868 | 
 869 | If you’re hosting your `build` with a static hosting provider you can use [react-snapshot](https://www.npmjs.com/package/react-snapshot) to generate HTML pages for each route, or relative link, in your application. These pages will then seamlessly become active, or “hydrated”, when the JavaScript bundle has loaded.
 870 | 
 871 | There are also opportunities to use this outside of static hosting, to take the pressure off the server when generating and caching routes.
 872 | 
 873 | The primary benefit of pre-rendering is that you get the core content of each page _with_ the HTML payload—regardless of whether or not your JavaScript bundle successfully downloads. It also increases the likelihood that each route of your application will be picked up by search engines.
 874 | 
 875 | You can read more about [zero-configuration pre-rendering (also called snapshotting) here](https://medium.com/superhighfives/an-almost-static-stack-6df0a2791319).
 876 | 
 877 | ## Injecting Data from the Server into the Page
 878 | 
 879 | Similarly to the previous section, you can leave some placeholders in the HTML that inject global variables, for example:
 880 | 
 881 | ```js
 882 | <!doctype html>
 883 | <html lang="en">
 884 |   <head>
 885 |     <script>
 886 |       window.SERVER_DATA = __SERVER_DATA__;
 887 |     </script>
 888 | ```
 889 | 
 890 | Then, on the server, you can replace `__SERVER_DATA__` with a JSON of real data right before sending the response. The client code can then read `window.SERVER_DATA` to use it. **Make sure to [sanitize the JSON before sending it to the client](https://medium.com/node-security/the-most-common-xss-vulnerability-in-react-js-applications-2bdffbcc1fa0) as it makes your app vulnerable to XSS attacks.**
 891 | 
 892 | ## Running Tests
 893 | 
 894 | >Note: this feature is available with `react-scripts@0.3.0` and higher.<br>
 895 | >[Read the migration guide to learn how to enable it in older projects!](https://github.com/facebookincubator/create-react-app/blob/master/CHANGELOG.md#migrating-from-023-to-030)
 896 | 
 897 | Create React App uses [Jest](https://facebook.github.io/jest/) as its test runner. To prepare for this integration, we did a [major revamp](https://facebook.github.io/jest/blog/2016/09/01/jest-15.html) of Jest so if you heard bad things about it years ago, give it another try.
 898 | 
 899 | Jest is a Node-based runner. This means that the tests always run in a Node environment and not in a real browser. This lets us enable fast iteration speed and prevent flakiness.
 900 | 
 901 | While Jest provides browser globals such as `window` thanks to [jsdom](https://github.com/tmpvar/jsdom), they are only approximations of the real browser behavior. Jest is intended to be used for unit tests of your logic and your components rather than the DOM quirks.
 902 | 
 903 | We recommend that you use a separate tool for browser end-to-end tests if you need them. They are beyond the scope of Create React App.
 904 | 
 905 | ### Filename Conventions
 906 | 
 907 | Jest will look for test files with any of the following popular naming conventions:
 908 | 
 909 | * Files with `.js` suffix in `__tests__` folders.
 910 | * Files with `.test.js` suffix.
 911 | * Files with `.spec.js` suffix.
 912 | 
 913 | The `.test.js` / `.spec.js` files (or the `__tests__` folders) can be located at any depth under the `src` top level folder.
 914 | 
 915 | We recommend to put the test files (or `__tests__` folders) next to the code they are testing so that relative imports appear shorter. For example, if `App.test.js` and `App.js` are in the same folder, the test just needs to `import App from './App'` instead of a long relative path. Colocation also helps find tests more quickly in larger projects.
 916 | 
 917 | ### Command Line Interface
 918 | 
 919 | When you run `npm test`, Jest will launch in the watch mode. Every time you save a file, it will re-run the tests, just like `npm start` recompiles the code.
 920 | 
 921 | The watcher includes an interactive command-line interface with the ability to run all tests, or focus on a search pattern. It is designed this way so that you can keep it open and enjoy fast re-runs. You can learn the commands from the “Watch Usage” note that the watcher prints after every run:
 922 | 
 923 | ![Jest watch mode](http://facebook.github.io/jest/img/blog/15-watch.gif)
 924 | 
 925 | ### Version Control Integration
 926 | 
 927 | By default, when you run `npm test`, Jest will only run the tests related to files changed since the last commit. This is an optimization designed to make your tests runs fast regardless of how many tests you have. However it assumes that you don’t often commit the code that doesn’t pass the tests.
 928 | 
 929 | Jest will always explicitly mention that it only ran tests related to the files changed since the last commit. You can also press `a` in the watch mode to force Jest to run all tests.
 930 | 
 931 | Jest will always run all tests on a [continuous integration](#continuous-integration) server or if the project is not inside a Git or Mercurial repository.
 932 | 
 933 | ### Writing Tests
 934 | 
 935 | To create tests, add `it()` (or `test()`) blocks with the name of the test and its code. You may optionally wrap them in `describe()` blocks for logical grouping but this is neither required nor recommended.
 936 | 
 937 | Jest provides a built-in `expect()` global function for making assertions. A basic test could look like this:
 938 | 
 939 | ```js
 940 | import sum from './sum';
 941 | 
 942 | it('sums numbers', () => {
 943 |   expect(sum(1, 2)).toEqual(3);
 944 |   expect(sum(2, 2)).toEqual(4);
 945 | });
 946 | ```
 947 | 
 948 | All `expect()` matchers supported by Jest are [extensively documented here](http://facebook.github.io/jest/docs/expect.html).<br>
 949 | You can also use [`jest.fn()` and `expect(fn).toBeCalled()`](http://facebook.github.io/jest/docs/expect.html#tohavebeencalled) to create “spies” or mock functions.
 950 | 
 951 | ### Testing Components
 952 | 
 953 | There is a broad spectrum of component testing techniques. They range from a “smoke test” verifying that a component renders without throwing, to shallow rendering and testing some of the output, to full rendering and testing component lifecycle and state changes.
 954 | 
 955 | Different projects choose different testing tradeoffs based on how often components change, and how much logic they contain. If you haven’t decided on a testing strategy yet, we recommend that you start with creating simple smoke tests for your components:
 956 | 
 957 | ```js
 958 | import React from 'react';
 959 | import ReactDOM from 'react-dom';
 960 | import App from './App';
 961 | 
 962 | it('renders without crashing', () => {
 963 |   const div = document.createElement('div');
 964 |   ReactDOM.render(<App />, div);
 965 | });
 966 | ```
 967 | 
 968 | This test mounts a component and makes sure that it didn’t throw during rendering. Tests like this provide a lot value with very little effort so they are great as a starting point, and this is the test you will find in `src/App.test.js`.
 969 | 
 970 | When you encounter bugs caused by changing components, you will gain a deeper insight into which parts of them are worth testing in your application. This might be a good time to introduce more specific tests asserting specific expected output or behavior.
 971 | 
 972 | If you’d like to test components in isolation from the child components they render, we recommend using [`shallow()` rendering API](http://airbnb.io/enzyme/docs/api/shallow.html) from [Enzyme](http://airbnb.io/enzyme/). You can write a smoke test with it too:
 973 | 
 974 | ```sh
 975 | npm install --save-dev enzyme react-addons-test-utils
 976 | ```
 977 | 
 978 | ```js
 979 | import React from 'react';
 980 | import { shallow } from 'enzyme';
 981 | import App from './App';
 982 | 
 983 | it('renders without crashing', () => {
 984 |   shallow(<App />);
 985 | });
 986 | ```
 987 | 
 988 | Unlike the previous smoke test using `ReactDOM.render()`, this test only renders `<App>` and doesn’t go deeper. For example, even if `<App>` itself renders a `<Button>` that throws, this test will pass. Shallow rendering is great for isolated unit tests, but you may still want to create some full rendering tests to ensure the components integrate correctly. Enzyme supports [full rendering with `mount()`](http://airbnb.io/enzyme/docs/api/mount.html), and you can also use it for testing state changes and component lifecycle.
 989 | 
 990 | You can read the [Enzyme documentation](http://airbnb.io/enzyme/) for more testing techniques. Enzyme documentation uses Chai and Sinon for assertions but you don’t have to use them because Jest provides built-in `expect()` and `jest.fn()` for spies.
 991 | 
 992 | Here is an example from Enzyme documentation that asserts specific output, rewritten to use Jest matchers:
 993 | 
 994 | ```js
 995 | import React from 'react';
 996 | import { shallow } from 'enzyme';
 997 | import App from './App';
 998 | 
 999 | it('renders welcome message', () => {
1000 |   const wrapper = shallow(<App />);
1001 |   const welcome = <h2>Welcome to React</h2>;
1002 |   // expect(wrapper.contains(welcome)).to.equal(true);
1003 |   expect(wrapper.contains(welcome)).toEqual(true);
1004 | });
1005 | ```
1006 | 
1007 | All Jest matchers are [extensively documented here](http://facebook.github.io/jest/docs/expect.html).<br>
1008 | Nevertheless you can use a third-party assertion library like [Chai](http://chaijs.com/) if you want to, as described below.
1009 | 
1010 | Additionally, you might find [jest-enzyme](https://github.com/blainekasten/enzyme-matchers) helpful to simplify your tests with readable matchers. The above `contains` code can be written simpler with jest-enzyme.
1011 | 
1012 | ```js
1013 | expect(wrapper).toContainReact(welcome)
1014 | ```
1015 | 
1016 | To setup jest-enzyme with Create React App, follow the instructions for [initializing your test environment](#initializing-test-environment) to import `jest-enzyme`.
1017 | 
1018 | ```sh
1019 | npm install --save-dev jest-enzyme
1020 | ```
1021 | 
1022 | ```js
1023 | // src/setupTests.js
1024 | import 'jest-enzyme';
1025 | ```
1026 | 
1027 | 
1028 | ### Using Third Party Assertion Libraries
1029 | 
1030 | We recommend that you use `expect()` for assertions and `jest.fn()` for spies. If you are having issues with them please [file those against Jest](https://github.com/facebook/jest/issues/new), and we’ll fix them. We intend to keep making them better for React, supporting, for example, [pretty-printing React elements as JSX](https://github.com/facebook/jest/pull/1566).
1031 | 
1032 | However, if you are used to other libraries, such as [Chai](http://chaijs.com/) and [Sinon](http://sinonjs.org/), or if you have existing code using them that you’d like to port over, you can import them normally like this:
1033 | 
1034 | ```js
1035 | import sinon from 'sinon';
1036 | import { expect } from 'chai';
1037 | ```
1038 | 
1039 | and then use them in your tests like you normally do.
1040 | 
1041 | ### Initializing Test Environment
1042 | 
1043 | >Note: this feature is available with `react-scripts@0.4.0` and higher.
1044 | 
1045 | If your app uses a browser API that you need to mock in your tests or if you just need a global setup before running your tests, add a `src/setupTests.js` to your project. It will be automatically executed before running your tests.
1046 | 
1047 | For example:
1048 | 
1049 | #### `src/setupTests.js`
1050 | ```js
1051 | const localStorageMock = {
1052 |   getItem: jest.fn(),
1053 |   setItem: jest.fn(),
1054 |   clear: jest.fn()
1055 | };
1056 | global.localStorage = localStorageMock
1057 | ```
1058 | 
1059 | ### Focusing and Excluding Tests
1060 | 
1061 | You can replace `it()` with `xit()` to temporarily exclude a test from being executed.<br>
1062 | Similarly, `fit()` lets you focus on a specific test without running any other tests.
1063 | 
1064 | ### Coverage Reporting
1065 | 
1066 | Jest has an integrated coverage reporter that works well with ES6 and requires no configuration.<br>
1067 | Run `npm test -- --coverage` (note extra `--` in the middle) to include a coverage report like this:
1068 | 
1069 | ![coverage report](http://i.imgur.com/5bFhnTS.png)
1070 | 
1071 | Note that tests run much slower with coverage so it is recommended to run it separately from your normal workflow.
1072 | 
1073 | ### Continuous Integration
1074 | 
1075 | By default `npm test` runs the watcher with interactive CLI. However, you can force it to run tests once and finish the process by setting an environment variable called `CI`.
1076 | 
1077 | When creating a build of your application with `npm run build` linter warnings are not checked by default. Like `npm test`, you can force the build to perform a linter warning check by setting the environment variable `CI`. If any warnings are encountered then the build fails.
1078 | 
1079 | Popular CI servers already set the environment variable `CI` by default but you can do this yourself too:
1080 | 
1081 | ### On CI servers
1082 | #### Travis CI
1083 | 
1084 | 1. Following the [Travis Getting started](https://docs.travis-ci.com/user/getting-started/) guide for syncing your GitHub repository with Travis.  You may need to initialize some settings manually in your [profile](https://travis-ci.org/profile) page.
1085 | 1. Add a `.travis.yml` file to your git repository.
1086 | ```
1087 | language: node_js
1088 | node_js:
1089 |   - 4
1090 |   - 6
1091 | cache:
1092 |   directories:
1093 |     - node_modules
1094 | script:
1095 |   - npm test
1096 |   - npm run build
1097 | ```
1098 | 1. Trigger your first build with a git push.
1099 | 1. [Customize your Travis CI Build](https://docs.travis-ci.com/user/customizing-the-build/) if needed.
1100 | 
1101 | ### On your own environment
1102 | ##### Windows (cmd.exe)
1103 | 
1104 | ```cmd
1105 | set CI=true&&npm test
1106 | ```
1107 | 
1108 | ```cmd
1109 | set CI=true&&npm run build
1110 | ```
1111 | 
1112 | (Note: the lack of whitespace is intentional.)
1113 | 
1114 | ##### Linux, macOS (Bash)
1115 | 
1116 | ```bash
1117 | CI=true npm test
1118 | ```
1119 | 
1120 | ```bash
1121 | CI=true npm run build
1122 | ```
1123 | 
1124 | The test command will force Jest to run tests once instead of launching the watcher.
1125 | 
1126 | >  If you find yourself doing this often in development, please [file an issue](https://github.com/facebookincubator/create-react-app/issues/new) to tell us about your use case because we want to make watcher the best experience and are open to changing how it works to accommodate more workflows.
1127 | 
1128 | The build command will check for linter warnings and fail if any are found.
1129 | 
1130 | ### Disabling jsdom
1131 | 
1132 | By default, the `package.json` of the generated project looks like this:
1133 | 
1134 | ```js
1135 |   // ...
1136 |   "scripts": {
1137 |     // ...
1138 |     "test": "react-scripts test --env=jsdom"
1139 |   }
1140 | ```
1141 | 
1142 | If you know that none of your tests depend on [jsdom](https://github.com/tmpvar/jsdom), you can safely remove `--env=jsdom`, and your tests will run faster.<br>
1143 | To help you make up your mind, here is a list of APIs that **need jsdom**:
1144 | 
1145 | * Any browser globals like `window` and `document`
1146 | * [`ReactDOM.render()`](https://facebook.github.io/react/docs/top-level-api.html#reactdom.render)
1147 | * [`TestUtils.renderIntoDocument()`](https://facebook.github.io/react/docs/test-utils.html#renderintodocument) ([a shortcut](https://github.com/facebook/react/blob/34761cf9a252964abfaab6faf74d473ad95d1f21/src/test/ReactTestUtils.js#L83-L91) for the above)
1148 | * [`mount()`](http://airbnb.io/enzyme/docs/api/mount.html) in [Enzyme](http://airbnb.io/enzyme/index.html)
1149 | 
1150 | In contrast, **jsdom is not needed** for the following APIs:
1151 | 
1152 | * [`TestUtils.createRenderer()`](https://facebook.github.io/react/docs/test-utils.html#shallow-rendering) (shallow rendering)
1153 | * [`shallow()`](http://airbnb.io/enzyme/docs/api/shallow.html) in [Enzyme](http://airbnb.io/enzyme/index.html)
1154 | 
1155 | Finally, jsdom is also not needed for [snapshot testing](http://facebook.github.io/jest/blog/2016/07/27/jest-14.html).
1156 | 
1157 | ### Snapshot Testing
1158 | 
1159 | Snapshot testing is a feature of Jest that automatically generates text snapshots of your components and saves them on the disk so if the UI output changes, you get notified without manually writing any assertions on the component output. [Read more about snapshot testing.](http://facebook.github.io/jest/blog/2016/07/27/jest-14.html)
1160 | 
1161 | ### Editor Integration
1162 | 
1163 | If you use [Visual Studio Code](https://code.visualstudio.com), there is a [Jest extension](https://github.com/orta/vscode-jest) which works with Create React App out of the box. This provides a lot of IDE-like features while using a text editor: showing the status of a test run with potential fail messages inline, starting and stopping the watcher automatically, and offering one-click snapshot updates.
1164 | 
1165 | ![VS Code Jest Preview](https://cloud.githubusercontent.com/assets/49038/20795349/a032308a-b7c8-11e6-9b34-7eeac781003f.png)
1166 | 
1167 | ## Developing Components in Isolation
1168 | 
1169 | Usually, in an app, you have a lot of UI components, and each of them has many different states.
1170 | For an example, a simple button component could have following states:
1171 | 
1172 | * With a text label.
1173 | * With an emoji.
1174 | * In the disabled mode.
1175 | 
1176 | Usually, it’s hard to see these states without running a sample app or some examples.
1177 | 
1178 | Create React App doesn’t include any tools for this by default, but you can easily add [React Storybook](https://github.com/kadirahq/react-storybook) to your project. **It is a third-party tool that lets you develop components and see all their states in isolation from your app**.
1179 | 
1180 | ![React Storybook Demo](http://i.imgur.com/7CIAWpB.gif)
1181 | 
1182 | You can also deploy your Storybook as a static app. This way, everyone in your team can view and review different states of UI components without starting a backend server or creating an account in your app.
1183 | 
1184 | **Here’s how to setup your app with Storybook:**
1185 | 
1186 | First, install the following npm package globally:
1187 | 
1188 | ```sh
1189 | npm install -g getstorybook
1190 | ```
1191 | 
1192 | Then, run the following command inside your app’s directory:
1193 | 
1194 | ```sh
1195 | getstorybook
1196 | ```
1197 | 
1198 | After that, follow the instructions on the screen.
1199 | 
1200 | Learn more about React Storybook:
1201 | 
1202 | * Screencast: [Getting Started with React Storybook](https://egghead.io/lessons/react-getting-started-with-react-storybook)
1203 | * [GitHub Repo](https://github.com/kadirahq/react-storybook)
1204 | * [Documentation](https://getstorybook.io/docs)
1205 | * [Snapshot Testing](https://github.com/kadirahq/storyshots) with React Storybook
1206 | 
1207 | ## Making a Progressive Web App
1208 | 
1209 | You can turn your React app into a [Progressive Web App](https://developers.google.com/web/progressive-web-apps/) by following the steps in [this repository](https://github.com/jeffposnick/create-react-pwa).
1210 | 
1211 | ## Deployment
1212 | 
1213 | `npm run build` creates a `build` directory with a production build of your app. Set up your favourite HTTP server so that a visitor to your site is served `index.html`, and requests to static paths like `/static/js/main.<hash>.js` are served with the contents of the `/static/js/main.<hash>.js` file.
1214 | 
1215 | ### Static Server
1216 | 
1217 | For environments using [Node](https://nodejs.org/), the easiest way to handle this would be to install [serve](https://github.com/zeit/serve) and let it handle the rest:
1218 | 
1219 | ```sh
1220 | npm install -g serve
1221 | serve -s build
1222 | ```
1223 | 
1224 | The last command shown above will serve your static site on the port **5000**. Like many of [serve](https://github.com/zeit/serve)’s internal settings, the port can be adjusted using the `-p` or `--port` flags.
1225 | 
1226 | Run this command to get a full list of the options available:
1227 | 
1228 | ```sh
1229 | serve -h
1230 | ```
1231 | 
1232 | ### Other Solutions
1233 | 
1234 | You don’t necessarily need a static server in order to run a Create React App project in production. It works just as fine integrated into an existing dynamic one.
1235 | 
1236 | Here’s a programmatic example using [Node](https://nodejs.org/) and [Express](http://expressjs.com/):
1237 | 
1238 | ```javascript
1239 | const express = require('express');
1240 | const path = require('path');
1241 | const app = express();
1242 | 
1243 | app.use(express.static('./build'));
1244 | 
1245 | app.get('/', function (req, res) {
1246 |   res.sendFile(path.join(__dirname, './build', 'index.html'));
1247 | });
1248 | 
1249 | app.listen(9000);
1250 | ```
1251 | 
1252 | The choice of your server software isn’t important either. Since Create React App is completely platform-agnostic, there’s no need to explicitly use Node.
1253 | 
1254 | The `build` folder with static assets is the only output produced by Create React App.
1255 | 
1256 | However this is not quite enough if you use client-side routing. Read the next section if you want to support URLs like `/todos/42` in your single-page app.
1257 | 
1258 | ### Serving Apps with Client-Side Routing
1259 | 
1260 | If you use routers that use the HTML5 [`pushState` history API](https://developer.mozilla.org/en-US/docs/Web/API/History_API#Adding_and_modifying_history_entries) under the hood (for example, [React Router](https://github.com/ReactTraining/react-router) with `browserHistory`), many static file servers will fail. For example, if you used React Router with a route for `/todos/42`, the development server will respond to `localhost:3000/todos/42` properly, but an Express serving a production build as above will not.
1261 | 
1262 | This is because when there is a fresh page load for a `/todos/42`, the server looks for the file `build/todos/42` and does not find it. The server needs to be configured to respond to a request to `/todos/42` by serving `index.html`. For example, we can amend our Express example above to serve `index.html` for any unknown paths:
1263 | 
1264 | ```diff
1265 |  app.use(express.static('./build'));
1266 | 
1267 | -app.get('/', function (req, res) {
1268 | +app.get('/*', function (req, res) {
1269 |    res.sendFile(path.join(__dirname, './build', 'index.html'));
1270 |  });
1271 | ```
1272 | 
1273 | If you’re using [Apache](https://httpd.apache.org/), you need to create a `.htaccess` file in the `public` folder that looks like this:
1274 | 
1275 | ```
1276 |     Options -MultiViews
1277 |     RewriteEngine On
1278 |     RewriteCond %{REQUEST_FILENAME} !-f
1279 |     RewriteRule ^ index.html [QSA,L]
1280 | ```
1281 | 
1282 | It will get copied to the `build` folder when you run `npm run build`.
1283 | 
1284 | Now requests to `/todos/42` will be handled correctly both in development and in production.
1285 | 
1286 | ### Building for Relative Paths
1287 | 
1288 | By default, Create React App produces a build assuming your app is hosted at the server root.<br>
1289 | To override this, specify the `homepage` in your `package.json`, for example:
1290 | 
1291 | ```js
1292 |   "homepage": "http://mywebsite.com/relativepath",
1293 | ```
1294 | 
1295 | This will let Create React App correctly infer the root path to use in the generated HTML file.
1296 | 
1297 | #### Serving the Same Build from Different Paths
1298 | 
1299 | >Note: this feature is available with `react-scripts@0.9.0` and higher.
1300 | 
1301 | If you are not using the HTML5 `pushState` history API or not using client-side routing at all, it is unnecessary to specify the URL from which your app will be served. Instead, you can put this in your `package.json`:
1302 | 
1303 | ```js
1304 |   "homepage": ".",
1305 | ```
1306 | 
1307 | This will make sure that all the asset paths are relative to `index.html`. You will then be able to move your app from `http://mywebsite.com` to `http://mywebsite.com/relativepath` or even `http://mywebsite.com/relative/path` without having to rebuild it.
1308 | 
1309 | ### Azure
1310 | 
1311 | See [this](https://medium.com/@to_pe/deploying-create-react-app-on-microsoft-azure-c0f6686a4321) blog post on how to deploy your React app to [Microsoft Azure](https://azure.microsoft.com/).
1312 | 
1313 | ### Firebase
1314 | 
1315 | Install the Firebase CLI if you haven’t already by running `npm install -g firebase-tools`. Sign up for a [Firebase account](https://console.firebase.google.com/) and create a new project. Run `firebase login` and login with your previous created Firebase account.
1316 | 
1317 | Then run the `firebase init` command from your project’s root. You need to choose the **Hosting: Configure and deploy Firebase Hosting sites** and choose the Firebase project you created in the previous step. You will need to agree with `database.rules.json` being created, choose `build` as the public directory, and also agree to **Configure as a single-page app** by replying with `y`.
1318 | 
1319 | ```sh
1320 |     === Project Setup
1321 | 
1322 |     First, let's associate this project directory with a Firebase project.
1323 |     You can create multiple project aliases by running firebase use --add,
1324 |     but for now we'll just set up a default project.
1325 | 
1326 |     ? What Firebase project do you want to associate as default? Example app (example-app-fd690)
1327 | 
1328 |     === Database Setup
1329 | 
1330 |     Firebase Realtime Database Rules allow you to define how your data should be
1331 |     structured and when your data can be read from and written to.
1332 | 
1333 |     ? What file should be used for Database Rules? database.rules.json
1334 |     ✔  Database Rules for example-app-fd690 have been downloaded to database.rules.json.
1335 |     Future modifications to database.rules.json will update Database Rules when you run
1336 |     firebase deploy.
1337 | 
1338 |     === Hosting Setup
1339 | 
1340 |     Your public directory is the folder (relative to your project directory) that
1341 |     will contain Hosting assets to uploaded with firebase deploy. If you
1342 |     have a build process for your assets, use your build's output directory.
1343 | 
1344 |     ? What do you want to use as your public directory? build
1345 |     ? Configure as a single-page app (rewrite all urls to /index.html)? Yes
1346 |     ✔  Wrote build/index.html
1347 | 
1348 |     i  Writing configuration info to firebase.json...
1349 |     i  Writing project information to .firebaserc...
1350 | 
1351 |     ✔  Firebase initialization complete!
1352 | ```
1353 | 
1354 | Now, after you create a production build with `npm run build`, you can deploy it by running `firebase deploy`.
1355 | 
1356 | ```sh
1357 |     === Deploying to 'example-app-fd690'...
1358 | 
1359 |     i  deploying database, hosting
1360 |     ✔  database: rules ready to deploy.
1361 |     i  hosting: preparing build directory for upload...
1362 |     Uploading: [==============================          ] 75%✔  hosting: build folder uploaded successfully
1363 |     ✔  hosting: 8 files uploaded successfully
1364 |     i  starting release process (may take several minutes)...
1365 | 
1366 |     ✔  Deploy complete!
1367 | 
1368 |     Project Console: https://console.firebase.google.com/project/example-app-fd690/overview
1369 |     Hosting URL: https://example-app-fd690.firebaseapp.com
1370 | ```
1371 | 
1372 | For more information see [Add Firebase to your JavaScript Project](https://firebase.google.com/docs/web/setup).
1373 | 
1374 | ### GitHub Pages
1375 | 
1376 | >Note: this feature is available with `react-scripts@0.2.0` and higher.
1377 | 
1378 | #### Step 1: Add `homepage` to `package.json`
1379 | 
1380 | **The step below is important!**<br>
1381 | **If you skip it, your app will not deploy correctly.**
1382 | 
1383 | Open your `package.json` and add a `homepage` field:
1384 | 
1385 | ```js
1386 |   "homepage": "https://myusername.github.io/my-app",
1387 | ```
1388 | 
1389 | Create React App uses the `homepage` field to determine the root URL in the built HTML file.
1390 | 
1391 | #### Step 2: Install `gh-pages` and add `deploy` to `scripts` in `package.json`
1392 | 
1393 | Now, whenever you run `npm run build`, you will see a cheat sheet with instructions on how to deploy to GitHub Pages.
1394 | 
1395 | To publish it at [https://myusername.github.io/my-app](https://myusername.github.io/my-app), run:
1396 | 
1397 | ```sh
1398 | npm install --save-dev gh-pages
1399 | ```
1400 | 
1401 | Add the following scripts in your `package.json`:
1402 | 
1403 | ```js
1404 |   // ...
1405 |   "scripts": {
1406 |     // ...
1407 |     "predeploy": "npm run build",
1408 |     "deploy": "gh-pages -d build"
1409 |   }
1410 | ```
1411 | 
1412 | The `predeploy` script will run automatically before `deploy` is run.
1413 | 
1414 | #### Step 3: Deploy the site by running `npm run deploy`
1415 | 
1416 | Then run:
1417 | 
1418 | ```sh
1419 | npm run deploy
1420 | ```
1421 | 
1422 | #### Step 4: Ensure your project’s settings use `gh-pages`
1423 | 
1424 | Finally, make sure **GitHub Pages** option in your GitHub project settings is set to use the `gh-pages` branch:
1425 | 
1426 | <img src="http://i.imgur.com/HUjEr9l.png" width="500" alt="gh-pages branch setting">
1427 | 
1428 | #### Step 5: Optionally, configure the domain
1429 | 
1430 | You can configure a custom domain with GitHub Pages by adding a `CNAME` file to the `public/` folder.
1431 | 
1432 | #### Notes on client-side routing
1433 | 
1434 | 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:
1435 | 
1436 | * 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.
1437 | * 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).
1438 | 
1439 | ### Heroku
1440 | 
1441 | Use the [Heroku Buildpack for Create React App](https://github.com/mars/create-react-app-buildpack).<br>
1442 | You can find instructions in [Deploying React with Zero Configuration](https://blog.heroku.com/deploying-react-with-zero-configuration).
1443 | 
1444 | #### Resolving Heroku Deployment Errors
1445 | 
1446 | Sometimes `npm run build` works locally but fails during deploy via Heroku. Following are the most common cases.
1447 | 
1448 | ##### "Module not found: Error: Cannot resolve 'file' or 'directory'"
1449 | 
1450 | If you get something like this:
1451 | 
1452 | ```
1453 | remote: Failed to create a production build. Reason:
1454 | remote: Module not found: Error: Cannot resolve 'file' or 'directory'
1455 | MyDirectory in /tmp/build_1234/src
1456 | ```
1457 | 
1458 | It means you need to ensure that the lettercase of the file or directory you `import` matches the one you see on your filesystem or on GitHub.
1459 | 
1460 | This is important because Linux (the operating system used by Heroku) is case sensitive. So `MyDirectory` and `mydirectory` are two distinct directories and thus, even though the project builds locally, the difference in case breaks the `import` statements on Heroku remotes.
1461 | 
1462 | ##### "Could not find a required file."
1463 | 
1464 | If you exclude or ignore necessary files from the package you will see a error similar this one:
1465 | 
1466 | ```
1467 | remote: Could not find a required file.
1468 | remote:   Name: `index.html`
1469 | remote:   Searched in: /tmp/build_a2875fc163b209225122d68916f1d4df/public
1470 | remote:
1471 | remote: npm ERR! Linux 3.13.0-105-generic
1472 | remote: npm ERR! argv "/tmp/build_a2875fc163b209225122d68916f1d4df/.heroku/node/bin/node" "/tmp/build_a2875fc163b209225122d68916f1d4df/.heroku/node/bin/npm" "run" "build"
1473 | ```
1474 | 
1475 | In this case, ensure that the file is there with the proper lettercase and that’s not ignored on your local `.gitignore` or `~/.gitignore_global`.
1476 | 
1477 | ### Modulus
1478 | 
1479 | See the [Modulus blog post](http://blog.modulus.io/deploying-react-apps-on-modulus) on how to deploy your react app to Modulus.
1480 | 
1481 | ## Netlify
1482 | 
1483 | **To do a manual deploy to Netlify’s CDN:**
1484 | 
1485 | ```sh
1486 | npm install netlify-cli
1487 | netlify deploy
1488 | ```
1489 | 
1490 | Choose `build` as the path to deploy.
1491 | 
1492 | **To setup continuous delivery:**
1493 | 
1494 | With this setup Netlify will build and deploy when you push to git or open a pull request:
1495 | 
1496 | 1. [Start a new netlify project](https://app.netlify.com/signup)
1497 | 2. Pick your Git hosting service and select your repository
1498 | 3. Click `Build your site`
1499 | 
1500 | **Support for client-side routing:**
1501 | 
1502 | To support `pushState`, make sure to create a `public/_redirects` file with the following rewrite rules:
1503 | 
1504 | ```
1505 | /*  /index.html  200
1506 | ```
1507 | 
1508 | When you build the project, Create React App will place the `public` folder contents into the build output.
1509 | 
1510 | ### Now
1511 | 
1512 | [now](https://zeit.co/now) offers a zero-configuration single-command deployment.
1513 | 
1514 | 1. Install the `now` command-line tool either via the recommended [desktop tool](https://zeit.co/download) or via node with `npm install -g now`.
1515 | 
1516 | 2. Install `serve` by running `npm install --save serve`.
1517 | 
1518 | 3. Add this line to `scripts` in `package.json`:
1519 |     
1520 |     ```
1521 |     "now-start": "serve build/",
1522 |     ```
1523 |     
1524 | 4. Run `now` from your project directory. You will see a **now.sh** URL in your output like this:
1525 |     
1526 |     ```
1527 |     > Ready! https://your-project-dirname-tpspyhtdtk.now.sh (copied to clipboard)
1528 |     ```
1529 |     
1530 |     Paste that URL into your browser when the build is complete, and you will see your deployed app.
1531 | 
1532 | Details are available in [this article.](https://zeit.co/blog/now-static)
1533 | 
1534 | ### S3 and CloudFront
1535 | 
1536 | See this [blog post](https://medium.com/@omgwtfmarc/deploying-create-react-app-to-s3-or-cloudfront-48dae4ce0af) on how to deploy your React app to Amazon Web Services [S3](https://aws.amazon.com/s3) and [CloudFront](https://aws.amazon.com/cloudfront/).
1537 | 
1538 | ### Surge
1539 | 
1540 | 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.
1541 | 
1542 | ```sh
1543 |               email: email@domain.com
1544 |            password: ********
1545 |        project path: /path/to/project/build
1546 |                size: 7 files, 1.8 MB
1547 |              domain: create-react-app.surge.sh
1548 |              upload: [====================] 100%, eta: 0.0s
1549 |    propagate on CDN: [====================] 100%
1550 |                plan: Free
1551 |               users: email@domain.com
1552 |          IP Address: X.X.X.X
1553 | 
1554 |     Success! Project is published and running at create-react-app.surge.sh
1555 | ```
1556 | 
1557 | 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).
1558 | 
1559 | ## Advanced Configuration
1560 | 
1561 | You can adjust various development and production settings by setting environment variables in your shell or with [.env](#adding-development-environment-variables-in-env).
1562 | 
1563 | Variable | Development | Production | Usage
1564 | :--- | :---: | :---: | :---
1565 | BROWSER | :white_check_mark: | :x: | By default, Create React App will open the default system browser, favoring Chrome on macOS. Specify a [browser](https://github.com/sindresorhus/opn#app) to override this behavior, or set it to `none` to disable it completely.
1566 | HOST | :white_check_mark: | :x: | By default, the development web server binds to `localhost`. You may use this variable to specify a different host.
1567 | PORT | :white_check_mark: | :x: | By default, the development web server will attempt to listen on port 3000 or prompt you to attempt the next available port. You may use this variable to specify a different port.
1568 | HTTPS | :white_check_mark: | :x: | When set to `true`, Create React App will run the development server in `https` mode.
1569 | PUBLIC_URL | :x: | :white_check_mark: | Create React App assumes your application is hosted at the serving web server's root or a subpath as specified in [`package.json` (`homepage`)](#building-for-relative-paths). Normally, Create React App ignores the hostname. You may use this variable to force assets to be referenced verbatim to the url you provide (hostname included). This may be particularly useful when using a CDN to host your application.
1570 | CI | :large_orange_diamond: | :white_check_mark: | When set to `true`, Create React App treats warnings as failures in the build. It also makes the test runner non-watching. Most CIs set this flag by default.
1571 | 
1572 | ## Troubleshooting
1573 | 
1574 | ### `npm start` doesn’t detect changes
1575 | 
1576 | When you save a file while `npm start` is running, the browser should refresh with the updated code.<br>
1577 | If this doesn’t happen, try one of the following workarounds:
1578 | 
1579 | * If your project is in a Dropbox folder, try moving it out.
1580 | * If the watcher doesn’t see a file called `index.js` and you’re referencing it by the folder name, you [need to restart the watcher](https://github.com/facebookincubator/create-react-app/issues/1164) due to a Webpack bug.
1581 | * Some editors like Vim and IntelliJ have a “safe write” feature that currently breaks the watcher. You will need to disable it. Follow the instructions in [“Working with editors supporting safe write”](https://webpack.github.io/docs/webpack-dev-server.html#working-with-editors-ides-supporting-safe-write).
1582 | * If your project path contains parentheses, try moving the project to a path without them. This is caused by a [Webpack watcher bug](https://github.com/webpack/watchpack/issues/42).
1583 | * On Linux and macOS, you might need to [tweak system settings](https://webpack.github.io/docs/troubleshooting.html#not-enough-watchers) to allow more watchers.
1584 | * If the project runs inside a virtual machine such as (a Vagrant provisioned) VirtualBox, create an `.env` file in your project directory if it doesn’t exist, and add `CHOKIDAR_USEPOLLING=true` to it. This ensures that the next time you run `npm start`, the watcher uses the polling mode, as necessary inside a VM.
1585 | 
1586 | If none of these solutions help please leave a comment [in this thread](https://github.com/facebookincubator/create-react-app/issues/659).
1587 | 
1588 | ### `npm test` hangs on macOS Sierra
1589 | 
1590 | If you run `npm test` and the console gets stuck after printing `react-scripts test --env=jsdom` to the console there might be a problem with your [Watchman](https://facebook.github.io/watchman/) installation as described in [facebookincubator/create-react-app#713](https://github.com/facebookincubator/create-react-app/issues/713).
1591 | 
1592 | We recommend deleting `node_modules` in your project and running `npm install` (or `yarn` if you use it) first. If it doesn't help, you can try one of the numerous workarounds mentioned in these issues:
1593 | 
1594 | * [facebook/jest#1767](https://github.com/facebook/jest/issues/1767)
1595 | * [facebook/watchman#358](https://github.com/facebook/watchman/issues/358)
1596 | * [ember-cli/ember-cli#6259](https://github.com/ember-cli/ember-cli/issues/6259)
1597 | 
1598 | It is reported that installing Watchman 4.7.0 or newer fixes the issue. If you use [Homebrew](http://brew.sh/), you can run these commands to update it:
1599 | 
1600 | ```
1601 | watchman shutdown-server
1602 | brew update
1603 | brew reinstall watchman
1604 | ```
1605 | 
1606 | You can find [other installation methods](https://facebook.github.io/watchman/docs/install.html#build-install) on the Watchman documentation page.
1607 | 
1608 | If this still doesn’t help, try running `launchctl unload -F ~/Library/LaunchAgents/com.github.facebook.watchman.plist`.
1609 | 
1610 | There are also reports that *uninstalling* Watchman fixes the issue. So if nothing else helps, remove it from your system and try again.
1611 | 
1612 | ### `npm run build` silently fails
1613 | 
1614 | It is reported that `npm run build` can fail on machines with no swap space, which is common in cloud environments. If [the symptoms are matching](https://github.com/facebookincubator/create-react-app/issues/1133#issuecomment-264612171), consider adding some swap space to the machine you’re building on, or build the project locally.
1615 | 
1616 | ### `npm run build` fails on Heroku
1617 | 
1618 | This may be a problem with case sensitive filenames.
1619 | Please refer to [this section](#resolving-heroku-deployment-errors).
1620 | 
1621 | ## Something Missing?
1622 | 
1623 | 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/packages/react-scripts/template/README.md)
1624 | 


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/audio-visuals/package.json:
--------------------------------------------------------------------------------
 1 | {
 2 |   "name": "audio-visuals",
 3 |   "version": "0.1.0",
 4 |   "private": true,
 5 |   "dependencies": {
 6 |     "react": "^15.4.2",
 7 |     "react-dom": "^15.4.2"
 8 |   },
 9 |   "devDependencies": {
10 |     "react-scripts": "0.9.5"
11 |   },
12 |   "scripts": {
13 |     "start": "react-scripts start",
14 |     "build": "react-scripts build",
15 |     "test": "react-scripts test --env=jsdom",
16 |     "eject": "react-scripts eject"
17 |   }
18 | }


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/audio-visuals/public/favicon.ico:
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https://raw.githubusercontent.com/elliehoward/react-audio-visualization/29adbce8d44a229c6ab6fd71a36ee931881c0abd/audio-visuals/public/favicon.ico


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/audio-visuals/public/index.html:
--------------------------------------------------------------------------------
 1 | <!doctype html>
 2 | <html lang="en">
 3 |   <head>
 4 |     <meta charset="utf-8">
 5 |     <meta name="viewport" content="width=device-width, initial-scale=1">
 6 |     <link rel="shortcut icon" href="%PUBLIC_URL%/favicon.ico">
 7 |     <!--
 8 |       Notice the use of %PUBLIC_URL% in the tag above.
 9 |       It will be replaced with the URL of the `public` folder during the build.
10 |       Only files inside the `public` folder can be referenced from the HTML.
11 | 
12 |       Unlike "/favicon.ico" or "favicon.ico", "%PUBLIC_URL%/favicon.ico" will
13 |       work correctly both with client-side routing and a non-root public URL.
14 |       Learn how to configure a non-root public URL by running `npm run build`.
15 |     -->
16 |     <title>React App</title>
17 |   </head>
18 |   <body>
19 |     <div id="root"></div>
20 |     <!--
21 |       This HTML file is a template.
22 |       If you open it directly in the browser, you will see an empty page.
23 | 
24 |       You can add webfonts, meta tags, or analytics to this file.
25 |       The build step will place the bundled scripts into the <body> tag.
26 | 
27 |       To begin the development, run `npm start`.
28 |       To create a production bundle, use `npm run build`.
29 |     -->
30 |   </body>
31 | </html>
32 | 


--------------------------------------------------------------------------------
/audio-visuals/src/App.css:
--------------------------------------------------------------------------------
 1 | .App {
 2 |   text-align: center;
 3 | }
 4 | 
 5 | .App-logo {
 6 |   animation: App-logo-spin infinite 20s linear;
 7 |   height: 80px;
 8 | }
 9 | 
10 | .App-header {
11 |   background-color: #222;
12 |   height: 150px;
13 |   padding: 20px;
14 |   color: white;
15 | }
16 | 
17 | .App-intro {
18 |   font-size: large;
19 | }
20 | 
21 | @keyframes App-logo-spin {
22 |   from { transform: rotate(0deg); }
23 |   to { transform: rotate(360deg); }
24 | }
25 | 


--------------------------------------------------------------------------------
/audio-visuals/src/App.js:
--------------------------------------------------------------------------------
 1 | import React, { Component } from 'react';
 2 | import './App.css';
 3 | 
 4 | class App extends Component {
 5 |     constructor(props){
 6 |         super(props)
 7 | 
 8 |         this.createVisualization = this.createVisualization.bind(this)
 9 |     }
10 | 
11 |     componentDidMount(){
12 |         this.createVisualization()
13 |     }
14 | 
15 |     createVisualization(){
16 |         let context = new AudioContext();
17 |         let analyser = context.createAnalyser();
18 |         let canvas = this.refs.analyzerCanvas;
19 |         let ctx = canvas.getContext('2d');
20 |         let audio = this.refs.audio;
21 |         audio.crossOrigin = "anonymous";
22 |         let audioSrc = context.createMediaElementSource(audio);
23 |         audioSrc.connect(analyser);
24 |         audioSrc.connect(context.destination);
25 |         analyser.connect(context.destination);
26 | 
27 |         function renderFrame(){
28 |             let freqData = new Uint8Array(analyser.frequencyBinCount)
29 |             requestAnimationFrame(renderFrame)
30 |             analyser.getByteFrequencyData(freqData)
31 |             ctx.clearRect(0, 0, canvas.width, canvas.height)
32 |             console.log(freqData)
33 |             ctx.fillStyle = '#9933ff';
34 |             let bars = 100;
35 |             for (var i = 0; i < bars; i++) {
36 |                 let bar_x = i * 3;
37 |                 let bar_width = 2;
38 |                 let bar_height = -(freqData[i] / 2);
39 |                 ctx.fillRect(bar_x, canvas.height, bar_width, bar_height)
40 |             }
41 |         };
42 |         renderFrame()
43 |     }
44 | 
45 |     render() {
46 |         return (
47 |             <div className="App">
48 |                 <h2>Sublime - 40oz to Freedom</h2>
49 |                 <div id="mp3_player">
50 |                     <div id="audio_box">
51 |                         <audio
52 |                             ref="audio"
53 |                             autoPlay={true}
54 |                             controls={true}
55 |                             //this is the link to my song url feel free to use it or replace it with your own
56 |                             src={"https://p.scdn.co/mp3-preview/e4a8f30ca62b4d2a129cc4df76de66f43e12fa3f?cid=null"}
57 |                             >
58 |                             </audio>
59 |                         </div>
60 |                         <canvas
61 |                             ref="analyzerCanvas"
62 |                             id="analyzer"
63 |                             >
64 |                             </canvas>
65 |                         </div>
66 |                     </div>
67 |                 );
68 |             }
69 |         }
70 | 
71 |         export default App;
72 | 


--------------------------------------------------------------------------------
/audio-visuals/src/App.test.js:
--------------------------------------------------------------------------------
1 | import React from 'react';
2 | import ReactDOM from 'react-dom';
3 | import App from './App';
4 | 
5 | it('renders without crashing', () => {
6 |   const div = document.createElement('div');
7 |   ReactDOM.render(<App />, div);
8 | });
9 | 


--------------------------------------------------------------------------------
/audio-visuals/src/index.css:
--------------------------------------------------------------------------------
1 | body {
2 |   margin: 0;
3 |   padding: 0;
4 |   font-family: sans-serif;
5 | }
6 | 


--------------------------------------------------------------------------------
/audio-visuals/src/index.js:
--------------------------------------------------------------------------------
 1 | import React from 'react';
 2 | import ReactDOM from 'react-dom';
 3 | import App from './App';
 4 | import './index.css';
 5 | 
 6 | ReactDOM.render(
 7 |   <App />,
 8 |   document.getElementById('root')
 9 | );
10 | 


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/audio-visuals/src/logo.svg:
--------------------------------------------------------------------------------
1 | <svg xmlns="http://www.w3.org/2000/svg" viewBox="0 0 841.9 595.3">
2 |     <g fill="#61DAFB">
3 |         <path d="M666.3 296.5c0-32.5-40.7-63.3-103.1-82.4 14.4-63.6 8-114.2-20.2-130.4-6.5-3.8-14.1-5.6-22.4-5.6v22.3c4.6 0 8.3.9 11.4 2.6 13.6 7.8 19.5 37.5 14.9 75.7-1.1 9.4-2.9 19.3-5.1 29.4-19.6-4.8-41-8.5-63.5-10.9-13.5-18.5-27.5-35.3-41.6-50 32.6-30.3 63.2-46.9 84-46.9V78c-27.5 0-63.5 19.6-99.9 53.6-36.4-33.8-72.4-53.2-99.9-53.2v22.3c20.7 0 51.4 16.5 84 46.6-14 14.7-28 31.4-41.3 49.9-22.6 2.4-44 6.1-63.6 11-2.3-10-4-19.7-5.2-29-4.7-38.2 1.1-67.9 14.6-75.8 3-1.8 6.9-2.6 11.5-2.6V78.5c-8.4 0-16 1.8-22.6 5.6-28.1 16.2-34.4 66.7-19.9 130.1-62.2 19.2-102.7 49.9-102.7 82.3 0 32.5 40.7 63.3 103.1 82.4-14.4 63.6-8 114.2 20.2 130.4 6.5 3.8 14.1 5.6 22.5 5.6 27.5 0 63.5-19.6 99.9-53.6 36.4 33.8 72.4 53.2 99.9 53.2 8.4 0 16-1.8 22.6-5.6 28.1-16.2 34.4-66.7 19.9-130.1 62-19.1 102.5-49.9 102.5-82.3zm-130.2-66.7c-3.7 12.9-8.3 26.2-13.5 39.5-4.1-8-8.4-16-13.1-24-4.6-8-9.5-15.8-14.4-23.4 14.2 2.1 27.9 4.7 41 7.9zm-45.8 106.5c-7.8 13.5-15.8 26.3-24.1 38.2-14.9 1.3-30 2-45.2 2-15.1 0-30.2-.7-45-1.9-8.3-11.9-16.4-24.6-24.2-38-7.6-13.1-14.5-26.4-20.8-39.8 6.2-13.4 13.2-26.8 20.7-39.9 7.8-13.5 15.8-26.3 24.1-38.2 14.9-1.3 30-2 45.2-2 15.1 0 30.2.7 45 1.9 8.3 11.9 16.4 24.6 24.2 38 7.6 13.1 14.5 26.4 20.8 39.8-6.3 13.4-13.2 26.8-20.7 39.9zm32.3-13c5.4 13.4 10 26.8 13.8 39.8-13.1 3.2-26.9 5.9-41.2 8 4.9-7.7 9.8-15.6 14.4-23.7 4.6-8 8.9-16.1 13-24.1zM421.2 430c-9.3-9.6-18.6-20.3-27.8-32 9 .4 18.2.7 27.5.7 9.4 0 18.7-.2 27.8-.7-9 11.7-18.3 22.4-27.5 32zm-74.4-58.9c-14.2-2.1-27.9-4.7-41-7.9 3.7-12.9 8.3-26.2 13.5-39.5 4.1 8 8.4 16 13.1 24 4.7 8 9.5 15.8 14.4 23.4zM420.7 163c9.3 9.6 18.6 20.3 27.8 32-9-.4-18.2-.7-27.5-.7-9.4 0-18.7.2-27.8.7 9-11.7 18.3-22.4 27.5-32zm-74 58.9c-4.9 7.7-9.8 15.6-14.4 23.7-4.6 8-8.9 16-13 24-5.4-13.4-10-26.8-13.8-39.8 13.1-3.1 26.9-5.8 41.2-7.9zm-90.5 125.2c-35.4-15.1-58.3-34.9-58.3-50.6 0-15.7 22.9-35.6 58.3-50.6 8.6-3.7 18-7 27.7-10.1 5.7 19.6 13.2 40 22.5 60.9-9.2 20.8-16.6 41.1-22.2 60.6-9.9-3.1-19.3-6.5-28-10.2zM310 490c-13.6-7.8-19.5-37.5-14.9-75.7 1.1-9.4 2.9-19.3 5.1-29.4 19.6 4.8 41 8.5 63.5 10.9 13.5 18.5 27.5 35.3 41.6 50-32.6 30.3-63.2 46.9-84 46.9-4.5-.1-8.3-1-11.3-2.7zm237.2-76.2c4.7 38.2-1.1 67.9-14.6 75.8-3 1.8-6.9 2.6-11.5 2.6-20.7 0-51.4-16.5-84-46.6 14-14.7 28-31.4 41.3-49.9 22.6-2.4 44-6.1 63.6-11 2.3 10.1 4.1 19.8 5.2 29.1zm38.5-66.7c-8.6 3.7-18 7-27.7 10.1-5.7-19.6-13.2-40-22.5-60.9 9.2-20.8 16.6-41.1 22.2-60.6 9.9 3.1 19.3 6.5 28.1 10.2 35.4 15.1 58.3 34.9 58.3 50.6-.1 15.7-23 35.6-58.4 50.6zM320.8 78.4z"/>
4 |         <circle cx="420.9" cy="296.5" r="45.7"/>
5 |         <path d="M520.5 78.1z"/>
6 |     </g>
7 | </svg>
8 | 


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