1 This project was bootstrapped with [Create React App](https://github.com/facebookincubator/create-react-app).
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).
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 Browsers](#supported-browsers)
17 - [Supported Language Features and Polyfills](#supported-language-features-and-polyfills)
18 - [Syntax Highlighting in the Editor](#syntax-highlighting-in-the-editor)
19 - [Displaying Lint Output in the Editor](#displaying-lint-output-in-the-editor)
20 - [Debugging in the Editor](#debugging-in-the-editor)
21 - [Formatting Code Automatically](#formatting-code-automatically)
22 - [Changing the Page `<title>`](#changing-the-page-title)
23 - [Installing a Dependency](#installing-a-dependency)
24 - [Importing a Component](#importing-a-component)
25 - [Code Splitting](#code-splitting)
26 - [Adding a Stylesheet](#adding-a-stylesheet)
27 - [Post-Processing CSS](#post-processing-css)
28 - [Adding a CSS Preprocessor (Sass, Less etc.)](#adding-a-css-preprocessor-sass-less-etc)
29 - [Adding Images, Fonts, and Files](#adding-images-fonts-and-files)
30 - [Using the `public` Folder](#using-the-public-folder)
31 - [Changing the HTML](#changing-the-html)
32 - [Adding Assets Outside of the Module System](#adding-assets-outside-of-the-module-system)
33 - [When to Use the `public` Folder](#when-to-use-the-public-folder)
34 - [Using Global Variables](#using-global-variables)
35 - [Adding Bootstrap](#adding-bootstrap)
36 - [Using a Custom Theme](#using-a-custom-theme)
37 - [Adding Flow](#adding-flow)
38 - [Adding a Router](#adding-a-router)
39 - [Adding Custom Environment Variables](#adding-custom-environment-variables)
40 - [Referencing Environment Variables in the HTML](#referencing-environment-variables-in-the-html)
41 - [Adding Temporary Environment Variables In Your Shell](#adding-temporary-environment-variables-in-your-shell)
42 - [Adding Development Environment Variables In `.env`](#adding-development-environment-variables-in-env)
43 - [Can I Use Decorators?](#can-i-use-decorators)
44 - [Fetching Data with AJAX Requests](#fetching-data-with-ajax-requests)
45 - [Integrating with an API Backend](#integrating-with-an-api-backend)
47 - [Ruby on Rails](#ruby-on-rails)
48 - [Proxying API Requests in Development](#proxying-api-requests-in-development)
49 - ["Invalid Host Header" Errors After Configuring Proxy](#invalid-host-header-errors-after-configuring-proxy)
50 - [Configuring the Proxy Manually](#configuring-the-proxy-manually)
51 - [Configuring a WebSocket Proxy](#configuring-a-websocket-proxy)
52 - [Using HTTPS in Development](#using-https-in-development)
53 - [Generating Dynamic `<meta>` Tags on the Server](#generating-dynamic-meta-tags-on-the-server)
54 - [Pre-Rendering into Static HTML Files](#pre-rendering-into-static-html-files)
55 - [Injecting Data from the Server into the Page](#injecting-data-from-the-server-into-the-page)
56 - [Running Tests](#running-tests)
57 - [Filename Conventions](#filename-conventions)
58 - [Command Line Interface](#command-line-interface)
59 - [Version Control Integration](#version-control-integration)
60 - [Writing Tests](#writing-tests)
61 - [Testing Components](#testing-components)
62 - [Using Third Party Assertion Libraries](#using-third-party-assertion-libraries)
63 - [Initializing Test Environment](#initializing-test-environment)
64 - [Focusing and Excluding Tests](#focusing-and-excluding-tests)
65 - [Coverage Reporting](#coverage-reporting)
66 - [Continuous Integration](#continuous-integration)
67 - [Disabling jsdom](#disabling-jsdom)
68 - [Snapshot Testing](#snapshot-testing)
69 - [Editor Integration](#editor-integration)
70 - [Debugging Tests](#debugging-tests)
71 - [Debugging Tests in Chrome](#debugging-tests-in-chrome)
72 - [Debugging Tests in Visual Studio Code](#debugging-tests-in-visual-studio-code)
73 - [Developing Components in Isolation](#developing-components-in-isolation)
74 - [Getting Started with Storybook](#getting-started-with-storybook)
75 - [Getting Started with Styleguidist](#getting-started-with-styleguidist)
76 - [Publishing Components to npm](#publishing-components-to-npm)
77 - [Making a Progressive Web App](#making-a-progressive-web-app)
78 - [Opting Out of Caching](#opting-out-of-caching)
79 - [Offline-First Considerations](#offline-first-considerations)
80 - [Progressive Web App Metadata](#progressive-web-app-metadata)
81 - [Analyzing the Bundle Size](#analyzing-the-bundle-size)
82 - [Deployment](#deployment)
83 - [Static Server](#static-server)
84 - [Other Solutions](#other-solutions)
85 - [Serving Apps with Client-Side Routing](#serving-apps-with-client-side-routing)
86 - [Building for Relative Paths](#building-for-relative-paths)
88 - [Firebase](#firebase)
89 - [GitHub Pages](#github-pages)
93 - [S3 and CloudFront](#s3-and-cloudfront)
95 - [Advanced Configuration](#advanced-configuration)
96 - [Troubleshooting](#troubleshooting)
97 - [`npm start` doesn’t detect changes](#npm-start-doesnt-detect-changes)
98 - [`npm test` hangs on macOS Sierra](#npm-test-hangs-on-macos-sierra)
99 - [`npm run build` exits too early](#npm-run-build-exits-too-early)
100 - [`npm run build` fails on Heroku](#npm-run-build-fails-on-heroku)
101 - [`npm run build` fails to minify](#npm-run-build-fails-to-minify)
102 - [Moment.js locales are missing](#momentjs-locales-are-missing)
103 - [Alternatives to Ejecting](#alternatives-to-ejecting)
104 - [Something Missing?](#something-missing)
106 ## Updating to New Releases
108 Create React App is divided into two packages:
110 * `create-react-app` is a global command-line utility that you use to create new projects.
111 * `react-scripts` is a development dependency in the generated projects (including this one).
113 You almost never need to update `create-react-app` itself: it delegates all the setup to `react-scripts`.
115 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.
117 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.
119 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.
121 We commit to keeping the breaking changes minimal so you can upgrade `react-scripts` painlessly.
125 We are always open to [your feedback](https://github.com/facebookincubator/create-react-app/issues).
129 After creation, your project should look like this:
148 For the project to build, **these files must exist with exact filenames**:
150 * `public/index.html` is the page template;
151 * `src/index.js` is the JavaScript entry point.
153 You can delete or rename the other files.
155 You may create subdirectories inside `src`. For faster rebuilds, only files inside `src` are processed by Webpack.<br>
156 You need to **put any JS and CSS files inside `src`**, otherwise Webpack won’t see them.
158 Only files inside `public` can be used from `public/index.html`.<br>
159 Read instructions below for using assets from JavaScript and HTML.
161 You can, however, create more top-level directories.<br>
162 They will not be included in the production build so you can use them for things like documentation.
166 In the project directory, you can run:
170 Runs the app in the development mode.<br>
171 Open [http://localhost:3000](http://localhost:3000) to view it in the browser.
173 The page will reload if you make edits.<br>
174 You will also see any lint errors in the console.
178 Launches the test runner in the interactive watch mode.<br>
179 See the section about [running tests](#running-tests) for more information.
183 Builds the app for production to the `build` folder.<br>
184 It correctly bundles React in production mode and optimizes the build for the best performance.
186 The build is minified and the filenames include the hashes.<br>
187 Your app is ready to be deployed!
189 See the section about [deployment](#deployment) for more information.
193 **Note: this is a one-way operation. Once you `eject`, you can’t go back!**
195 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.
197 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.
199 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.
201 ## Supported Browsers
203 By default, the generated project uses the latest version of React.
205 You can refer [to the React documentation](https://reactjs.org/docs/react-dom.html#browser-support) for more information about supported browsers.
207 ## Supported Language Features and Polyfills
209 This project supports a superset of the latest JavaScript standard.<br>
210 In addition to [ES6](https://github.com/lukehoban/es6features) syntax features, it also supports:
212 * [Exponentiation Operator](https://github.com/rwaldron/exponentiation-operator) (ES2016).
213 * [Async/await](https://github.com/tc39/ecmascript-asyncawait) (ES2017).
214 * [Object Rest/Spread Properties](https://github.com/sebmarkbage/ecmascript-rest-spread) (stage 3 proposal).
215 * [Dynamic import()](https://github.com/tc39/proposal-dynamic-import) (stage 3 proposal)
216 * [Class Fields and Static Properties](https://github.com/tc39/proposal-class-public-fields) (part of stage 3 proposal).
217 * [JSX](https://facebook.github.io/react/docs/introducing-jsx.html) and [Flow](https://flowtype.org/) syntax.
219 Learn more about [different proposal stages](https://babeljs.io/docs/plugins/#presets-stage-x-experimental-presets-).
221 While we recommend using 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.
223 Note that **the project only includes a few ES6 [polyfills](https://en.wikipedia.org/wiki/Polyfill)**:
225 * [`Object.assign()`](https://developer.mozilla.org/en/docs/Web/JavaScript/Reference/Global_Objects/Object/assign) via [`object-assign`](https://github.com/sindresorhus/object-assign).
226 * [`Promise`](https://developer.mozilla.org/en-US/docs/Web/JavaScript/Reference/Global_Objects/Promise) via [`promise`](https://github.com/then/promise).
227 * [`fetch()`](https://developer.mozilla.org/en/docs/Web/API/Fetch_API) via [`whatwg-fetch`](https://github.com/github/fetch).
229 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.
231 Also note that using some newer syntax features like `for...of` or `[...nonArrayValue]` causes Babel to emit code that depends on ES6 runtime features and might not work without a polyfill. When in doubt, use [Babel REPL](https://babeljs.io/repl/) to see what any specific syntax compiles down to.
233 ## Syntax Highlighting in the Editor
235 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.
237 ## Displaying Lint Output in the Editor
239 >Note: this feature is available with `react-scripts@0.2.0` and higher.<br>
240 >It also only works with npm 3 or higher.
242 Some editors, including Sublime Text, Atom, and Visual Studio Code, provide plugins for ESLint.
244 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.
246 You would need to install an ESLint plugin for your editor first. Then, add a file called `.eslintrc` to the project root:
250 "extends": "react-app"
254 Now your editor should report the linting warnings.
256 Note that even if you edit your `.eslintrc` file further, these changes will **only affect the editor integration**. They won’t affect the terminal and in-browser lint output. This is because Create React App intentionally provides a minimal set of rules that find common mistakes.
258 If you want to enforce a coding style for your project, consider using [Prettier](https://github.com/jlongster/prettier) instead of ESLint style rules.
260 ## Debugging in the Editor
262 **This feature is currently only supported by [Visual Studio Code](https://code.visualstudio.com) and [WebStorm](https://www.jetbrains.com/webstorm/).**
264 Visual Studio Code and WebStorm support 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.
266 ### Visual Studio Code
268 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.
270 Then add the block below to your `launch.json` file and put it inside the `.vscode` folder in your app’s root directory.
279 "url": "http://localhost:3000",
280 "webRoot": "${workspaceRoot}/src",
281 "sourceMapPathOverrides": {
282 "webpack:///src/*": "${webRoot}/*"
287 >Note: the URL may be different if you've made adjustments via the [HOST or PORT environment variables](#advanced-configuration).
289 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.
291 Having problems with VS Code Debugging? Please see their [troubleshooting guide](https://github.com/Microsoft/vscode-chrome-debug/blob/master/README.md#troubleshooting).
295 You would need to have [WebStorm](https://www.jetbrains.com/webstorm/) and [JetBrains IDE Support](https://chrome.google.com/webstore/detail/jetbrains-ide-support/hmhgeddbohgjknpmjagkdomcpobmllji) Chrome extension installed.
297 In the WebStorm menu `Run` select `Edit Configurations...`. Then click `+` and select `JavaScript Debug`. Paste `http://localhost:3000` into the URL field and save the configuration.
299 >Note: the URL may be different if you've made adjustments via the [HOST or PORT environment variables](#advanced-configuration).
301 Start your app by running `npm start`, then press `^D` on macOS or `F9` on Windows and Linux or click the green debug icon to start debugging in WebStorm.
303 The same way you can debug your application in IntelliJ IDEA Ultimate, PhpStorm, PyCharm Pro, and RubyMine.
305 ## Formatting Code Automatically
307 Prettier is an opinionated code formatter with support for JavaScript, CSS and JSON. With Prettier you can format the code you write automatically to ensure a code style within your project. See the [Prettier's GitHub page](https://github.com/prettier/prettier) for more information, and look at this [page to see it in action](https://prettier.github.io/prettier/).
309 To format our code whenever we make a commit in git, we need to install the following dependencies:
312 npm install --save husky lint-staged prettier
315 Alternatively you may use `yarn`:
318 yarn add husky lint-staged prettier
321 * `husky` makes it easy to use githooks as if they are npm scripts.
322 * `lint-staged` allows us to run scripts on staged files in git. See this [blog post about lint-staged to learn more about it](https://medium.com/@okonetchnikov/make-linting-great-again-f3890e1ad6b8).
323 * `prettier` is the JavaScript formatter we will run before commits.
325 Now we can make sure every file is formatted correctly by adding a few lines to the `package.json` in the project root.
327 Add the following line to `scripts` section:
331 + "precommit": "lint-staged",
332 "start": "react-scripts start",
333 "build": "react-scripts build",
336 Next we add a 'lint-staged' field to the `package.json`, for example:
343 + "src/**/*.{js,jsx,json,css}": [
344 + "prettier --single-quote --write",
351 Now, whenever you make a commit, Prettier will format the changed files automatically. You can also run `./node_modules/.bin/prettier --single-quote --write "src/**/*.{js,jsx,json,css}"` to format your entire project for the first time.
353 Next you might want to integrate Prettier in your favorite editor. Read the section on [Editor Integration](https://prettier.io/docs/en/editors.html) on the Prettier GitHub page.
355 ## Changing the Page `<title>`
357 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.
359 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.
361 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.
363 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).
365 ## Installing a Dependency
367 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`:
370 npm install --save react-router
373 Alternatively you may use `yarn`:
376 yarn add react-router
379 This works for any library, not just `react-router`.
381 ## Importing a Component
383 This project setup supports ES6 modules thanks to Babel.<br>
384 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.
391 import React, { Component } from 'react';
393 class Button extends Component {
399 export default Button; // Don’t forget to use export default!
402 ### `DangerButton.js`
406 import React, { Component } from 'react';
407 import Button from './Button'; // Import a component from another file
409 class DangerButton extends Component {
411 return <Button color="red" />;
415 export default DangerButton;
418 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.
420 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'`.
422 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.
424 Learn more about ES6 modules:
426 * [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)
427 * [Exploring ES6: Modules](http://exploringjs.com/es6/ch_modules.html)
428 * [Understanding ES6: Modules](https://leanpub.com/understandinges6/read#leanpub-auto-encapsulating-code-with-modules)
432 Instead of downloading the entire app before users can use it, code splitting allows you to split your code into small chunks which you can then load on demand.
434 This project setup supports code splitting via [dynamic `import()`](http://2ality.com/2017/01/import-operator.html#loading-code-on-demand). Its [proposal](https://github.com/tc39/proposal-dynamic-import) is in stage 3. The `import()` function-like form takes the module name as an argument and returns a [`Promise`](https://developer.mozilla.org/en-US/docs/Web/JavaScript/Reference/Global_Objects/Promise) which always resolves to the namespace object of the module.
441 const moduleA = 'Hello';
448 import React, { Component } from 'react';
450 class App extends Component {
451 handleClick = () => {
453 .then(({ moduleA }) => {
464 <button onClick={this.handleClick}>Load</button>
473 This will make `moduleA.js` and all its unique dependencies as a separate chunk that only loads after the user clicks the 'Load' button.
475 You can also use it with `async` / `await` syntax if you prefer it.
477 ### With React Router
479 If you are using React Router check out [this tutorial](http://serverless-stack.com/chapters/code-splitting-in-create-react-app.html) on how to use code splitting with it. You can find the companion GitHub repository [here](https://github.com/AnomalyInnovations/serverless-stack-demo-client/tree/code-splitting-in-create-react-app).
481 Also check out the [Code Splitting](https://reactjs.org/docs/code-splitting.html) section in React documentation.
483 ## Adding a Stylesheet
485 This project setup uses [Webpack](https://webpack.js.org/) 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**:
498 import React, { Component } from 'react';
499 import './Button.css'; // Tell Webpack that Button.js uses these styles
501 class Button extends Component {
503 // You can use them as regular CSS styles
504 return <div className="Button" />;
509 **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.
511 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.
513 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.
515 ## Post-Processing CSS
517 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.
533 display: -webkit-box;
534 display: -ms-flexbox;
536 -webkit-box-orient: horizontal;
537 -webkit-box-direction: normal;
538 -ms-flex-direction: row;
540 -webkit-box-align: center;
541 -ms-flex-align: center;
546 If you need to disable autoprefixing for some reason, [follow this section](https://github.com/postcss/autoprefixer#disabling).
548 ## Adding a CSS Preprocessor (Sass, Less etc.)
550 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)).
552 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.
554 First, let’s install the command-line interface for Sass:
557 npm install --save node-sass-chokidar
560 Alternatively you may use `yarn`:
563 yarn add node-sass-chokidar
566 Then in `package.json`, add the following lines to `scripts`:
570 + "build-css": "node-sass-chokidar src/ -o src/",
571 + "watch-css": "npm run build-css && node-sass-chokidar src/ -o src/ --watch --recursive",
572 "start": "react-scripts start",
573 "build": "react-scripts build",
574 "test": "react-scripts test --env=jsdom",
577 >Note: To use a different preprocessor, replace `build-css` and `watch-css` commands according to your preprocessor’s documentation.
579 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.
581 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.
583 To enable importing files without using relative paths, you can add the `--include-path` option to the command in `package.json`.
586 "build-css": "node-sass-chokidar --include-path ./src --include-path ./node_modules src/ -o src/",
587 "watch-css": "npm run build-css && node-sass-chokidar --include-path ./src --include-path ./node_modules src/ -o src/ --watch --recursive",
590 This will allow you to do imports like
593 @import 'styles/_colors.scss'; // assuming a styles directory under src/
594 @import 'nprogress/nprogress'; // importing a css file from the nprogress node module
597 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.
599 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:
602 npm install --save npm-run-all
605 Alternatively you may use `yarn`:
611 Then we can change `start` and `build` scripts to include the CSS preprocessor commands:
615 "build-css": "node-sass-chokidar src/ -o src/",
616 "watch-css": "npm run build-css && node-sass-chokidar src/ -o src/ --watch --recursive",
617 - "start": "react-scripts start",
618 - "build": "react-scripts build",
619 + "start-js": "react-scripts start",
620 + "start": "npm-run-all -p watch-css start-js",
621 + "build-js": "react-scripts build",
622 + "build": "npm-run-all build-css build-js",
623 "test": "react-scripts test --env=jsdom",
624 "eject": "react-scripts eject"
628 Now running `npm start` and `npm run build` also builds Sass files.
630 **Why `node-sass-chokidar`?**
632 `node-sass` has been reported as having the following issues:
634 - `node-sass --watch` has been reported to have *performance issues* in certain conditions when used in a virtual machine or with docker.
636 - Infinite styles compiling [#1939](https://github.com/facebookincubator/create-react-app/issues/1939)
638 - `node-sass` has been reported as having issues with detecting new files in a directory [#1891](https://github.com/sass/node-sass/issues/1891)
640 `node-sass-chokidar` is used here as it addresses these issues.
642 ## Adding Images, Fonts, and Files
644 With Webpack, using static assets like images and fonts works similarly to CSS.
646 You can **`import` a file right in a JavaScript module**. This tells Webpack to include that file in the bundle. Unlike CSS imports, importing a file gives you a string value. This value is the final path you can reference in your code, e.g. as the `src` attribute of an image or the `href` of a link to a PDF.
648 To reduce the number of requests to the server, importing images that are less than 10,000 bytes returns a [data URI](https://developer.mozilla.org/en-US/docs/Web/HTTP/Basics_of_HTTP/Data_URIs) instead of a path. This applies to the following file extensions: bmp, gif, jpg, jpeg, and png. SVG files are excluded due to [#1153](https://github.com/facebookincubator/create-react-app/issues/1153).
653 import React from 'react';
654 import logo from './logo.png'; // Tell Webpack this JS file uses this image
656 console.log(logo); // /logo.84287d09.png
659 // Import result is the URL of your image
660 return <img src={logo} alt="Logo" />;
663 export default Header;
666 This ensures that when the project is built, Webpack will correctly move the images into the build folder, and provide us with correct paths.
668 This works in CSS too:
672 background-image: url(./logo.png);
676 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.
678 Please be advised that this is also a custom feature of Webpack.
680 **It is not required for React** but many people enjoy it (and React Native uses a similar mechanism for images).<br>
681 An alternative way of handling static assets is described in the next section.
683 ## Using the `public` Folder
685 >Note: this feature is available with `react-scripts@0.5.0` and higher.
687 ### Changing the HTML
689 The `public` folder contains the HTML file so you can tweak it, for example, to [set the page title](#changing-the-page-title).
690 The `<script>` tag with the compiled code will be added to it automatically during the build process.
692 ### Adding Assets Outside of the Module System
694 You can also add other assets to the `public` folder.
696 Note that we normally encourage you to `import` assets in JavaScript files instead.
697 For example, see the sections on [adding a stylesheet](#adding-a-stylesheet) and [adding images and fonts](#adding-images-fonts-and-files).
698 This mechanism provides a number of benefits:
700 * Scripts and stylesheets get minified and bundled together to avoid extra network requests.
701 * Missing files cause compilation errors instead of 404 errors for your users.
702 * Result filenames include content hashes so you don’t need to worry about browsers caching their old versions.
704 However there is an **escape hatch** that you can use to add an asset outside of the module system.
706 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`.
708 Inside `index.html`, you can use it like this:
711 <link rel="shortcut icon" href="%PUBLIC_URL%/favicon.ico">
714 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.
716 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.
718 In JavaScript code, you can use `process.env.PUBLIC_URL` for similar purposes:
722 // Note: this is an escape hatch and should be used sparingly!
723 // Normally we recommend using `import` for getting asset URLs
724 // as described in “Adding Images and Fonts” above this section.
725 return <img src={process.env.PUBLIC_URL + '/img/logo.png'} />;
729 Keep in mind the downsides of this approach:
731 * None of the files in `public` folder get post-processed or minified.
732 * Missing files will not be called at compilation time, and will cause 404 errors for your users.
733 * Result filenames won’t include content hashes so you’ll need to add query arguments or rename them every time they change.
735 ### When to Use the `public` Folder
737 Normally we recommend importing [stylesheets](#adding-a-stylesheet), [images, and fonts](#adding-images-fonts-and-files) from JavaScript.
738 The `public` folder is useful as a workaround for a number of less common cases:
740 * 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).
741 * You have thousands of images and need to dynamically reference their paths.
742 * You want to include a small script like [`pace.js`](http://github.hubspot.com/pace/docs/welcome/) outside of the bundled code.
743 * Some library may be incompatible with Webpack and you have no other option but to include it as a `<script>` tag.
745 Note that if you add a `<script>` that declares global variables, you also need to read the next section on using them.
747 ## Using Global Variables
749 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.
751 You can avoid this by reading the global variable explicitly from the `window` object, for example:
757 This makes it obvious you are using a global variable intentionally rather than because of a typo.
759 Alternatively, you can force the linter to ignore any line by adding `// eslint-disable-line` after it.
763 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:
765 Install React Bootstrap and Bootstrap from npm. React Bootstrap does not include Bootstrap CSS so this needs to be installed as well:
768 npm install --save react-bootstrap bootstrap@3
771 Alternatively you may use `yarn`:
774 yarn add react-bootstrap bootstrap@3
777 Import Bootstrap CSS and optionally Bootstrap theme CSS in the beginning of your ```src/index.js``` file:
780 import 'bootstrap/dist/css/bootstrap.css';
781 import 'bootstrap/dist/css/bootstrap-theme.css';
782 // Put any other imports below so that CSS from your
783 // components takes precedence over default styles.
786 Import required React Bootstrap components within ```src/App.js``` file or your custom component files:
789 import { Navbar, Jumbotron, Button } from 'react-bootstrap';
792 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.
794 ### Using a Custom Theme
796 Sometimes you might need to tweak the visual styles of Bootstrap (or equivalent package).<br>
797 We suggest the following approach:
799 * Create a new package that depends on the package you wish to customize, e.g. Bootstrap.
800 * Add the necessary build steps to tweak the theme, and publish your package on npm.
801 * Install your own theme npm package as a dependency of your app.
803 Here is an example of adding a [customized Bootstrap](https://medium.com/@tacomanator/customizing-create-react-app-aa9ffb88165) that follows these steps.
807 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.
809 Recent versions of [Flow](http://flowtype.org/) work with Create React App projects out of the box.
811 To add Flow to a Create React App project, follow these steps:
813 1. Run `npm install --save flow-bin` (or `yarn add flow-bin`).
814 2. Add `"flow": "flow"` to the `scripts` section of your `package.json`.
815 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.
816 4. Add `// @flow` to any files you want to type check (for example, to `src/App.js`).
818 Now you can run `npm run flow` (or `yarn flow`) to check the files for type errors.
819 You can optionally use an IDE like [Nuclide](https://nuclide.io/docs/languages/flow/) for a better integrated experience.
820 In the future we plan to integrate it into Create React App even more closely.
822 To learn more about Flow, check out [its documentation](https://flowtype.org/).
826 Create React App doesn't prescribe a specific routing solution, but [React Router](https://reacttraining.com/react-router/) is the most popular one.
831 npm install --save react-router-dom
834 Alternatively you may use `yarn`:
837 yarn add react-router-dom
840 To try it, delete all the code in `src/App.js` and replace it with any of the examples on its website. The [Basic Example](https://reacttraining.com/react-router/web/example/basic) is a good place to get started.
842 Note that [you may need to configure your production server to support client-side routing](#serving-apps-with-client-side-routing) before deploying your app.
844 ## Adding Custom Environment Variables
846 >Note: this feature is available with `react-scripts@0.2.3` and higher.
848 Your project can consume variables declared in your environment as if they were declared locally in your JS files. By
849 default you will have `NODE_ENV` defined for you, and any other environment variables starting with
852 **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.
854 >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.
856 These environment variables will be defined for you on `process.env`. For example, having an environment
857 variable named `REACT_APP_SECRET_CODE` will be exposed in your JS as `process.env.REACT_APP_SECRET_CODE`.
859 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.
861 These environment variables can be useful for displaying information conditionally based on where the project is
862 deployed or consuming sensitive data that lives outside of version control.
864 First, you need to have environment variables defined. For example, let’s say you wanted to consume a secret defined
865 in the environment inside a `<form>`:
871 <small>You are running this application in <b>{process.env.NODE_ENV}</b> mode.</small>
873 <input type="hidden" defaultValue={process.env.REACT_APP_SECRET_CODE} />
880 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.
882 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`:
886 <small>You are running this application in <b>development</b> mode.</small>
888 <input type="hidden" value="abcdef" />
893 The above form is looking for a variable called `REACT_APP_SECRET_CODE` from the environment. In order to consume this
894 value, we need to have it defined in the environment. This can be done using two ways: either in your shell or in
895 a `.env` file. Both of these ways are described in the next few sections.
897 Having access to the `NODE_ENV` is also useful for performing actions conditionally:
900 if (process.env.NODE_ENV !== 'production') {
905 When you compile the app with `npm run build`, the minification step will strip out this condition, and the resulting bundle will be smaller.
907 ### Referencing Environment Variables in the HTML
909 >Note: this feature is available with `react-scripts@0.9.0` and higher.
911 You can also access the environment variables starting with `REACT_APP_` in the `public/index.html`. For example:
914 <title>%REACT_APP_WEBSITE_NAME%</title>
917 Note that the caveats from the above section apply:
919 * Apart from a few built-in variables (`NODE_ENV` and `PUBLIC_URL`), variable names must start with `REACT_APP_` to work.
920 * 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).
922 ### Adding Temporary Environment Variables In Your Shell
924 Defining environment variables can vary between OSes. It’s also important to know that this manner is temporary for the
925 life of the shell session.
927 #### Windows (cmd.exe)
930 set "REACT_APP_SECRET_CODE=abcdef" && npm start
933 (Note: Quotes around the variable assignment are required to avoid a trailing whitespace.)
935 #### Windows (Powershell)
938 ($env:REACT_APP_SECRET_CODE = "abcdef") -and (npm start)
941 #### Linux, macOS (Bash)
944 REACT_APP_SECRET_CODE=abcdef npm start
947 ### Adding Development Environment Variables In `.env`
949 >Note: this feature is available with `react-scripts@0.5.0` and higher.
951 To define permanent environment variables, create a file called `.env` in the root of your project:
954 REACT_APP_SECRET_CODE=abcdef
956 >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.
958 `.env` files **should be** checked into source control (with the exclusion of `.env*.local`).
960 #### What other `.env` files can be used?
962 >Note: this feature is **available with `react-scripts@1.0.0` and higher**.
965 * `.env.local`: Local overrides. **This file is loaded for all environments except test.**
966 * `.env.development`, `.env.test`, `.env.production`: Environment-specific settings.
967 * `.env.development.local`, `.env.test.local`, `.env.production.local`: Local overrides of environment-specific settings.
969 Files on the left have more priority than files on the right:
971 * `npm start`: `.env.development.local`, `.env.development`, `.env.local`, `.env`
972 * `npm run build`: `.env.production.local`, `.env.production`, `.env.local`, `.env`
973 * `npm test`: `.env.test.local`, `.env.test`, `.env` (note `.env.local` is missing)
975 These variables will act as the defaults if the machine does not explicitly set them.<br>
976 Please refer to the [dotenv documentation](https://github.com/motdotla/dotenv) for more details.
978 >Note: If you are defining environment variables for development, your CI and/or hosting platform will most likely need
979 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).
981 #### Expanding Environment Variables In `.env`
983 >Note: this feature is available with `react-scripts@1.1.0` and higher.
985 Expand variables already on your machine for use in your `.env` file (using [dotenv-expand](https://github.com/motdotla/dotenv-expand)).
987 For example, to get the environment variable `npm_package_version`:
990 REACT_APP_VERSION=$npm_package_version
992 # REACT_APP_VERSION=${npm_package_version}
995 Or expand variables local to the current `.env` file:
998 DOMAIN=www.example.com
999 REACT_APP_FOO=$DOMAIN/foo
1000 REACT_APP_BAR=$DOMAIN/bar
1003 ## Can I Use Decorators?
1005 Many popular libraries use [decorators](https://medium.com/google-developers/exploring-es7-decorators-76ecb65fb841) in their documentation.<br>
1006 Create React App doesn’t support decorator syntax at the moment because:
1008 * It is an experimental proposal and is subject to change.
1009 * The current specification version is not officially supported by Babel.
1010 * If the specification changes, we won’t be able to write a codemod because we don’t use them internally at Facebook.
1012 However in many cases you can rewrite decorator-based code without decorators just as fine.<br>
1013 Please refer to these two threads for reference:
1015 * [#214](https://github.com/facebookincubator/create-react-app/issues/214)
1016 * [#411](https://github.com/facebookincubator/create-react-app/issues/411)
1018 Create React App will add decorator support when the specification advances to a stable stage.
1020 ## Fetching Data with AJAX Requests
1022 React doesn't prescribe a specific approach to data fetching, but people commonly use either a library like [axios](https://github.com/axios/axios) or the [`fetch()` API](https://developer.mozilla.org/en-US/docs/Web/API/Fetch_API) provided by the browser. Conveniently, Create React App includes a polyfill for `fetch()` so you can use it without worrying about the browser support.
1024 The global `fetch` function allows to easily makes AJAX requests. It takes in a URL as an input and returns a `Promise` that resolves to a `Response` object. You can find more information about `fetch` [here](https://developer.mozilla.org/en-US/docs/Web/API/Fetch_API/Using_Fetch).
1026 This project also includes a [Promise polyfill](https://github.com/then/promise) which provides a full implementation of Promises/A+. A Promise represents the eventual result of an asynchronous operation, you can find more information about Promises [here](https://www.promisejs.org/) and [here](https://developer.mozilla.org/en-US/docs/Web/JavaScript/Reference/Global_Objects/Promise). Both axios and `fetch()` use Promises under the hood. You can also use the [`async / await`](https://davidwalsh.name/async-await) syntax to reduce the callback nesting.
1028 You can learn more about making AJAX requests from React components in [the FAQ entry on the React website](https://reactjs.org/docs/faq-ajax.html).
1030 ## Integrating with an API Backend
1032 These tutorials will help you to integrate your app with an API backend running on another port,
1033 using `fetch()` to access it.
1036 Check out [this tutorial](https://www.fullstackreact.com/articles/using-create-react-app-with-a-server/).
1037 You can find the companion GitHub repository [here](https://github.com/fullstackreact/food-lookup-demo).
1041 Check out [this tutorial](https://www.fullstackreact.com/articles/how-to-get-create-react-app-to-work-with-your-rails-api/).
1042 You can find the companion GitHub repository [here](https://github.com/fullstackreact/food-lookup-demo-rails).
1044 ## Proxying API Requests in Development
1046 >Note: this feature is available with `react-scripts@0.2.3` and higher.
1048 People often serve the front-end React app from the same host and port as their backend implementation.<br>
1049 For example, a production setup might look like this after the app is deployed:
1052 / - static server returns index.html with React app
1053 /todos - static server returns index.html with React app
1054 /api/todos - server handles any /api/* requests using the backend implementation
1057 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.
1059 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:
1062 "proxy": "http://localhost:4000",
1065 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 `text/html` in its `Accept` header to the proxy.
1067 Conveniently, this avoids [CORS issues](http://stackoverflow.com/questions/21854516/understanding-ajax-cors-and-security-considerations) and error messages like this in development:
1070 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.
1073 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`.
1075 The `proxy` option supports HTTP, HTTPS and WebSocket connections.<br>
1076 If the `proxy` option is **not** flexible enough for you, alternatively you can:
1078 * [Configure the proxy yourself](#configuring-the-proxy-manually)
1079 * Enable CORS on your server ([here’s how to do it for Express](http://enable-cors.org/server_expressjs.html)).
1080 * Use [environment variables](#adding-custom-environment-variables) to inject the right server host and port into your app.
1082 ### "Invalid Host Header" Errors After Configuring Proxy
1084 When you enable the `proxy` option, you opt into a more strict set of host checks. This is necessary because leaving the backend open to remote hosts makes your computer vulnerable to DNS rebinding attacks. The issue is explained in [this article](https://medium.com/webpack/webpack-dev-server-middleware-security-issues-1489d950874a) and [this issue](https://github.com/webpack/webpack-dev-server/issues/887).
1086 This shouldn’t affect you when developing on `localhost`, but if you develop remotely like [described here](https://github.com/facebookincubator/create-react-app/issues/2271), you will see this error in the browser after enabling the `proxy` option:
1088 >Invalid Host header
1090 To work around it, you can specify your public development host in a file called `.env.development` in the root of your project:
1093 HOST=mypublicdevhost.com
1096 If you restart the development server now and load the app from the specified host, it should work.
1098 If you are still having issues or if you’re using a more exotic environment like a cloud editor, you can bypass the host check completely by adding a line to `.env.development.local`. **Note that this is dangerous and exposes your machine to remote code execution from malicious websites:**
1101 # NOTE: THIS IS DANGEROUS!
1102 # It exposes your machine to attacks from the websites you visit.
1103 DANGEROUSLY_DISABLE_HOST_CHECK=true
1106 We don’t recommend this approach.
1108 ### Configuring the Proxy Manually
1110 >Note: this feature is available with `react-scripts@1.0.0` and higher.
1112 If the `proxy` option is **not** flexible enough for you, you can specify an object in the following form (in `package.json`).<br>
1113 You may also specify any configuration value [`http-proxy-middleware`](https://github.com/chimurai/http-proxy-middleware#options) or [`http-proxy`](https://github.com/nodejitsu/node-http-proxy#options) supports.
1128 All requests matching this path will be proxies, no exceptions. This includes requests for `text/html`, which the standard `proxy` option does not proxy.
1130 If you need to specify multiple proxies, you may do so by specifying additional entries.
1131 Matches are regular expressions, so that you can use a regexp to match multiple paths.
1136 // Matches any request starting with /api
1138 "target": "<url_1>",
1142 // Matches any request starting with /foo
1144 "target": "<url_2>",
1147 "^/foo": "/foo/beta"
1151 // Matches /bar/abc.html but not /bar/sub/def.html
1152 "/bar/[^/]*[.]html": {
1153 "target": "<url_3>",
1156 // Matches /baz/abc.html and /baz/sub/def.html
1157 "/baz/.*/.*[.]html": {
1166 ### Configuring a WebSocket Proxy
1168 When setting up a WebSocket proxy, there are a some extra considerations to be aware of.
1170 If you’re using a WebSocket engine like [Socket.io](https://socket.io/), you must have a Socket.io server running that you can use as the proxy target. Socket.io will not work with a standard WebSocket server. Specifically, don't expect Socket.io to work with [the websocket.org echo test](http://websocket.org/echo.html).
1172 There’s some good documentation available for [setting up a Socket.io server](https://socket.io/docs/).
1174 Standard WebSockets **will** work with a standard WebSocket server as well as the websocket.org echo test. You can use libraries like [ws](https://github.com/websockets/ws) for the server, with [native WebSockets in the browser](https://developer.mozilla.org/en-US/docs/Web/API/WebSocket).
1176 Either way, you can proxy WebSocket requests manually in `package.json`:
1183 // Your compatible WebSocket server
1184 "target": "ws://<socket_url>",
1185 // Tell http-proxy-middleware that this is a WebSocket proxy.
1186 // Also allows you to proxy WebSocket requests without an additional HTTP request
1187 // https://github.com/chimurai/http-proxy-middleware#external-websocket-upgrade
1196 ## Using HTTPS in Development
1198 >Note: this feature is available with `react-scripts@0.4.0` and higher.
1200 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.
1202 To do this, set the `HTTPS` environment variable to `true`, then start the dev server as usual with `npm start`:
1204 #### Windows (cmd.exe)
1207 set HTTPS=true&&npm start
1210 #### Windows (Powershell)
1213 ($env:HTTPS = $true) -and (npm start)
1216 (Note: the lack of whitespace is intentional.)
1218 #### Linux, macOS (Bash)
1221 HTTPS=true npm start
1224 Note that the server will use a self-signed certificate, so your web browser will almost definitely display a warning upon accessing the page.
1226 ## Generating Dynamic `<meta>` Tags on the Server
1228 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:
1234 <meta property="og:title" content="__OG_TITLE__">
1235 <meta property="og:description" content="__OG_DESCRIPTION__">
1238 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!
1240 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.
1242 ## Pre-Rendering into Static HTML Files
1244 If you’re hosting your `build` with a static hosting provider you can use [react-snapshot](https://www.npmjs.com/package/react-snapshot) or [react-snap](https://github.com/stereobooster/react-snap) 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.
1246 There are also opportunities to use this outside of static hosting, to take the pressure off the server when generating and caching routes.
1248 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.
1250 You can read more about [zero-configuration pre-rendering (also called snapshotting) here](https://medium.com/superhighfives/an-almost-static-stack-6df0a2791319).
1252 ## Injecting Data from the Server into the Page
1254 Similarly to the previous section, you can leave some placeholders in the HTML that inject global variables, for example:
1261 window.SERVER_DATA = __SERVER_DATA__;
1265 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.**
1269 >Note: this feature is available with `react-scripts@0.3.0` and higher.<br>
1270 >[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)
1272 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.
1274 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.
1276 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.
1278 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.
1280 ### Filename Conventions
1282 Jest will look for test files with any of the following popular naming conventions:
1284 * Files with `.js` suffix in `__tests__` folders.
1285 * Files with `.test.js` suffix.
1286 * Files with `.spec.js` suffix.
1288 The `.test.js` / `.spec.js` files (or the `__tests__` folders) can be located at any depth under the `src` top level folder.
1290 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.
1292 ### Command Line Interface
1294 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.
1296 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:
1298 ![Jest watch mode](http://facebook.github.io/jest/img/blog/15-watch.gif)
1300 ### Version Control Integration
1302 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 run 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.
1304 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.
1306 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.
1310 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.
1312 Jest provides a built-in `expect()` global function for making assertions. A basic test could look like this:
1315 import sum from './sum';
1317 it('sums numbers', () => {
1318 expect(sum(1, 2)).toEqual(3);
1319 expect(sum(2, 2)).toEqual(4);
1323 All `expect()` matchers supported by Jest are [extensively documented here](https://facebook.github.io/jest/docs/en/expect.html#content).<br>
1324 You can also use [`jest.fn()` and `expect(fn).toBeCalled()`](https://facebook.github.io/jest/docs/en/expect.html#tohavebeencalled) to create “spies” or mock functions.
1326 ### Testing Components
1328 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.
1330 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:
1333 import React from 'react';
1334 import ReactDOM from 'react-dom';
1335 import App from './App';
1337 it('renders without crashing', () => {
1338 const div = document.createElement('div');
1339 ReactDOM.render(<App />, div);
1343 This test mounts a component and makes sure that it didn’t throw during rendering. Tests like this provide a lot of 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`.
1345 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.
1347 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/). To install it, run:
1350 npm install --save enzyme enzyme-adapter-react-16 react-test-renderer
1353 Alternatively you may use `yarn`:
1356 yarn add enzyme enzyme-adapter-react-16 react-test-renderer
1359 As of Enzyme 3, you will need to install Enzyme along with an Adapter corresponding to the version of React you are using. (The examples above use the adapter for React 16.)
1361 The adapter will also need to be configured in your [global setup file](#initializing-test-environment):
1363 #### `src/setupTests.js`
1365 import { configure } from 'enzyme';
1366 import Adapter from 'enzyme-adapter-react-16';
1368 configure({ adapter: new Adapter() });
1371 >Note: Keep in mind that if you decide to "eject" before creating `src/setupTests.js`, the resulting `package.json` file won't contain any reference to it. [Read here](#initializing-test-environment) to learn how to add this after ejecting.
1373 Now you can write a smoke test with it:
1376 import React from 'react';
1377 import { shallow } from 'enzyme';
1378 import App from './App';
1380 it('renders without crashing', () => {
1385 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.
1387 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.
1389 Here is an example from Enzyme documentation that asserts specific output, rewritten to use Jest matchers:
1392 import React from 'react';
1393 import { shallow } from 'enzyme';
1394 import App from './App';
1396 it('renders welcome message', () => {
1397 const wrapper = shallow(<App />);
1398 const welcome = <h2>Welcome to React</h2>;
1399 // expect(wrapper.contains(welcome)).to.equal(true);
1400 expect(wrapper.contains(welcome)).toEqual(true);
1404 All Jest matchers are [extensively documented here](http://facebook.github.io/jest/docs/en/expect.html).<br>
1405 Nevertheless you can use a third-party assertion library like [Chai](http://chaijs.com/) if you want to, as described below.
1407 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 more simply with jest-enzyme.
1410 expect(wrapper).toContainReact(welcome)
1413 To enable this, install `jest-enzyme`:
1416 npm install --save jest-enzyme
1419 Alternatively you may use `yarn`:
1422 yarn add jest-enzyme
1425 Import it in [`src/setupTests.js`](#initializing-test-environment) to make its matchers available in every test:
1428 import 'jest-enzyme';
1431 ### Using Third Party Assertion Libraries
1433 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).
1435 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:
1438 import sinon from 'sinon';
1439 import { expect } from 'chai';
1442 and then use them in your tests like you normally do.
1444 ### Initializing Test Environment
1446 >Note: this feature is available with `react-scripts@0.4.0` and higher.
1448 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.
1452 #### `src/setupTests.js`
1454 const localStorageMock = {
1459 global.localStorage = localStorageMock
1462 >Note: Keep in mind that if you decide to "eject" before creating `src/setupTests.js`, the resulting `package.json` file won't contain any reference to it, so you should manually create the property `setupTestFrameworkScriptFile` in the configuration for Jest, something like the following:
1467 > "setupTestFrameworkScriptFile": "<rootDir>/src/setupTests.js"
1471 ### Focusing and Excluding Tests
1473 You can replace `it()` with `xit()` to temporarily exclude a test from being executed.<br>
1474 Similarly, `fit()` lets you focus on a specific test without running any other tests.
1476 ### Coverage Reporting
1478 Jest has an integrated coverage reporter that works well with ES6 and requires no configuration.<br>
1479 Run `npm test -- --coverage` (note extra `--` in the middle) to include a coverage report like this:
1481 ![coverage report](http://i.imgur.com/5bFhnTS.png)
1483 Note that tests run much slower with coverage so it is recommended to run it separately from your normal workflow.
1487 The default Jest coverage configuration can be overriden by adding any of the following supported keys to a Jest config in your package.json.
1489 Supported overrides:
1490 - [`collectCoverageFrom`](https://facebook.github.io/jest/docs/en/configuration.html#collectcoveragefrom-array)
1491 - [`coverageReporters`](https://facebook.github.io/jest/docs/en/configuration.html#coveragereporters-array-string)
1492 - [`coverageThreshold`](https://facebook.github.io/jest/docs/en/configuration.html#coveragethreshold-object)
1493 - [`snapshotSerializers`](https://facebook.github.io/jest/docs/en/configuration.html#snapshotserializers-array-string)
1495 Example package.json:
1499 "name": "your-package",
1501 "collectCoverageFrom" : [
1502 "src/**/*.{js,jsx}",
1503 "!<rootDir>/node_modules/",
1504 "!<rootDir>/path/to/dir/"
1506 "coverageThreshold": {
1514 "coverageReporters": ["text"],
1515 "snapshotSerializers": ["my-serializer-module"]
1520 ### Continuous Integration
1522 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`.
1524 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.
1526 Popular CI servers already set the environment variable `CI` by default but you can do this yourself too:
1531 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.
1532 1. Add a `.travis.yml` file to your git repository.
1544 1. Trigger your first build with a git push.
1545 1. [Customize your Travis CI Build](https://docs.travis-ci.com/user/customizing-the-build/) if needed.
1549 Follow [this article](https://medium.com/@knowbody/circleci-and-zeits-now-sh-c9b7eebcd3c1) to set up CircleCI with a Create React App project.
1551 ### On your own environment
1552 ##### Windows (cmd.exe)
1555 set CI=true&&npm test
1559 set CI=true&&npm run build
1562 (Note: the lack of whitespace is intentional.)
1564 ##### Windows (Powershell)
1567 ($env:CI = $true) -and (npm test)
1571 ($env:CI = $true) -and (npm run build)
1574 ##### Linux, macOS (Bash)
1581 CI=true npm run build
1584 The test command will force Jest to run tests once instead of launching the watcher.
1586 > 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.
1588 The build command will check for linter warnings and fail if any are found.
1592 By default, the `package.json` of the generated project looks like this:
1596 "start": "react-scripts start",
1597 "build": "react-scripts build",
1598 "test": "react-scripts test --env=jsdom"
1601 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:
1605 "start": "react-scripts start",
1606 "build": "react-scripts build",
1607 - "test": "react-scripts test --env=jsdom"
1608 + "test": "react-scripts test"
1611 To help you make up your mind, here is a list of APIs that **need jsdom**:
1613 * Any browser globals like `window` and `document`
1614 * [`ReactDOM.render()`](https://facebook.github.io/react/docs/top-level-api.html#reactdom.render)
1615 * [`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)
1616 * [`mount()`](http://airbnb.io/enzyme/docs/api/mount.html) in [Enzyme](http://airbnb.io/enzyme/index.html)
1618 In contrast, **jsdom is not needed** for the following APIs:
1620 * [`TestUtils.createRenderer()`](https://facebook.github.io/react/docs/test-utils.html#shallow-rendering) (shallow rendering)
1621 * [`shallow()`](http://airbnb.io/enzyme/docs/api/shallow.html) in [Enzyme](http://airbnb.io/enzyme/index.html)
1623 Finally, jsdom is also not needed for [snapshot testing](http://facebook.github.io/jest/blog/2016/07/27/jest-14.html).
1625 ### Snapshot Testing
1627 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)
1629 ### Editor Integration
1631 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.
1633 ![VS Code Jest Preview](https://cloud.githubusercontent.com/assets/49038/20795349/a032308a-b7c8-11e6-9b34-7eeac781003f.png)
1637 There are various ways to setup a debugger for your Jest tests. We cover debugging in Chrome and [Visual Studio Code](https://code.visualstudio.com/).
1639 >Note: debugging tests requires Node 8 or higher.
1641 ### Debugging Tests in Chrome
1643 Add the following to the `scripts` section in your project's `package.json`
1646 "test:debug": "react-scripts --inspect-brk test --runInBand --env=jsdom"
1649 Place `debugger;` statements in any test and run:
1651 $ npm run test:debug
1654 This will start running your Jest tests, but pause before executing to allow a debugger to attach to the process.
1656 Open the following in Chrome
1661 After opening that link, the Chrome Developer Tools will be displayed. Select `inspect` on your process and a breakpoint will be set at the first line of the react script (this is done simply to give you time to open the developer tools and to prevent Jest from executing before you have time to do so). Click the button that looks like a "play" button in the upper right hand side of the screen to continue execution. When Jest executes the test that contains the debugger statement, execution will pause and you can examine the current scope and call stack.
1663 >Note: the --runInBand cli option makes sure Jest runs test in the same process rather than spawning processes for individual tests. Normally Jest parallelizes test runs across processes but it is hard to debug many processes at the same time.
1665 ### Debugging Tests in Visual Studio Code
1667 Debugging Jest tests is supported out of the box for [Visual Studio Code](https://code.visualstudio.com).
1669 Use the following [`launch.json`](https://code.visualstudio.com/docs/editor/debugging#_launch-configurations) configuration file:
1675 "name": "Debug CRA Tests",
1677 "request": "launch",
1678 "runtimeExecutable": "${workspaceRoot}/node_modules/.bin/react-scripts",
1685 "cwd": "${workspaceRoot}",
1686 "protocol": "inspector",
1687 "console": "integratedTerminal",
1688 "internalConsoleOptions": "neverOpen"
1694 ## Developing Components in Isolation
1696 Usually, in an app, you have a lot of UI components, and each of them has many different states.
1697 For an example, a simple button component could have following states:
1699 * In a regular state, with a text label.
1700 * In the disabled mode.
1701 * In a loading state.
1703 Usually, it’s hard to see these states without running a sample app or some examples.
1705 Create React App doesn’t include any tools for this by default, but you can easily add [Storybook for React](https://storybook.js.org) ([source](https://github.com/storybooks/storybook)) or [React Styleguidist](https://react-styleguidist.js.org/) ([source](https://github.com/styleguidist/react-styleguidist)) to your project. **These are third-party tools that let you develop components and see all their states in isolation from your app**.
1707 ![Storybook for React Demo](http://i.imgur.com/7CIAWpB.gif)
1709 You can also deploy your Storybook or style guide 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.
1711 ### Getting Started with Storybook
1713 Storybook is a development environment for React UI components. It allows you to browse a component library, view the different states of each component, and interactively develop and test components.
1715 First, install the following npm package globally:
1718 npm install -g @storybook/cli
1721 Then, run the following command inside your app’s directory:
1727 After that, follow the instructions on the screen.
1729 Learn more about React Storybook:
1731 * Screencast: [Getting Started with React Storybook](https://egghead.io/lessons/react-getting-started-with-react-storybook)
1732 * [GitHub Repo](https://github.com/storybooks/storybook)
1733 * [Documentation](https://storybook.js.org/basics/introduction/)
1734 * [Snapshot Testing UI](https://github.com/storybooks/storybook/tree/master/addons/storyshots) with Storybook + addon/storyshot
1736 ### Getting Started with Styleguidist
1738 Styleguidist combines a style guide, where all your components are presented on a single page with their props documentation and usage examples, with an environment for developing components in isolation, similar to Storybook. In Styleguidist you write examples in Markdown, where each code snippet is rendered as a live editable playground.
1740 First, install Styleguidist:
1743 npm install --save react-styleguidist
1746 Alternatively you may use `yarn`:
1749 yarn add react-styleguidist
1752 Then, add these scripts to your `package.json`:
1756 + "styleguide": "styleguidist server",
1757 + "styleguide:build": "styleguidist build",
1758 "start": "react-scripts start",
1761 Then, run the following command inside your app’s directory:
1767 After that, follow the instructions on the screen.
1769 Learn more about React Styleguidist:
1771 * [GitHub Repo](https://github.com/styleguidist/react-styleguidist)
1772 * [Documentation](https://react-styleguidist.js.org/docs/getting-started.html)
1774 ## Publishing Components to npm
1776 Create React App doesn't provide any built-in functionality to publish a component to npm. If you're ready to extract a component from your project so other people can use it, we recommend moving it to a separate directory outside of your project and then using a tool like [nwb](https://github.com/insin/nwb#react-components-and-libraries) to prepare it for publishing.
1778 ## Making a Progressive Web App
1780 By default, the production build is a fully functional, offline-first
1781 [Progressive Web App](https://developers.google.com/web/progressive-web-apps/).
1783 Progressive Web Apps are faster and more reliable than traditional web pages, and provide an engaging mobile experience:
1785 * All static site assets are cached so that your page loads fast on subsequent visits, regardless of network connectivity (such as 2G or 3G). Updates are downloaded in the background.
1786 * Your app will work regardless of network state, even if offline. This means your users will be able to use your app at 10,000 feet and on the subway.
1787 * On mobile devices, your app can be added directly to the user's home screen, app icon and all. You can also re-engage users using web **push notifications**. This eliminates the need for the app store.
1789 The [`sw-precache-webpack-plugin`](https://github.com/goldhand/sw-precache-webpack-plugin)
1790 is integrated into production configuration,
1791 and it will take care of generating a service worker file that will automatically
1792 precache all of your local assets and keep them up to date as you deploy updates.
1793 The service worker will use a [cache-first strategy](https://developers.google.com/web/fundamentals/instant-and-offline/offline-cookbook/#cache-falling-back-to-network)
1794 for handling all requests for local assets, including the initial HTML, ensuring
1795 that your web app is reliably fast, even on a slow or unreliable network.
1797 ### Opting Out of Caching
1799 If you would prefer not to enable service workers prior to your initial
1800 production deployment, then remove the call to `registerServiceWorker()`
1801 from [`src/index.js`](src/index.js).
1803 If you had previously enabled service workers in your production deployment and
1804 have decided that you would like to disable them for all your existing users,
1805 you can swap out the call to `registerServiceWorker()` in
1806 [`src/index.js`](src/index.js) first by modifying the service worker import:
1808 import { unregister } from './registerServiceWorker';
1810 and then call `unregister()` instead.
1811 After the user visits a page that has `unregister()`,
1812 the service worker will be uninstalled. Note that depending on how `/service-worker.js` is served,
1813 it may take up to 24 hours for the cache to be invalidated.
1815 ### Offline-First Considerations
1817 1. Service workers [require HTTPS](https://developers.google.com/web/fundamentals/getting-started/primers/service-workers#you_need_https),
1818 although to facilitate local testing, that policy
1819 [does not apply to `localhost`](http://stackoverflow.com/questions/34160509/options-for-testing-service-workers-via-http/34161385#34161385).
1820 If your production web server does not support HTTPS, then the service worker
1821 registration will fail, but the rest of your web app will remain functional.
1823 1. Service workers are [not currently supported](https://jakearchibald.github.io/isserviceworkerready/)
1824 in all web browsers. Service worker registration [won't be attempted](src/registerServiceWorker.js)
1825 on browsers that lack support.
1827 1. The service worker is only enabled in the [production environment](#deployment),
1828 e.g. the output of `npm run build`. It's recommended that you do not enable an
1829 offline-first service worker in a development environment, as it can lead to
1830 frustration when previously cached assets are used and do not include the latest
1831 changes you've made locally.
1833 1. If you *need* to test your offline-first service worker locally, build
1834 the application (using `npm run build`) and run a simple http server from your
1835 build directory. After running the build script, `create-react-app` will give
1836 instructions for one way to test your production build locally and the [deployment instructions](#deployment) have
1837 instructions for using other methods. *Be sure to always use an
1838 incognito window to avoid complications with your browser cache.*
1840 1. If possible, configure your production environment to serve the generated
1841 `service-worker.js` [with HTTP caching disabled](http://stackoverflow.com/questions/38843970/service-worker-javascript-update-frequency-every-24-hours).
1842 If that's not possible—[GitHub Pages](#github-pages), for instance, does not
1843 allow you to change the default 10 minute HTTP cache lifetime—then be aware
1844 that if you visit your production site, and then revisit again before
1845 `service-worker.js` has expired from your HTTP cache, you'll continue to get
1846 the previously cached assets from the service worker. If you have an immediate
1847 need to view your updated production deployment, performing a shift-refresh
1848 will temporarily disable the service worker and retrieve all assets from the
1851 1. Users aren't always familiar with offline-first web apps. It can be useful to
1852 [let the user know](https://developers.google.com/web/fundamentals/instant-and-offline/offline-ux#inform_the_user_when_the_app_is_ready_for_offline_consumption)
1853 when the service worker has finished populating your caches (showing a "This web
1854 app works offline!" message) and also let them know when the service worker has
1855 fetched the latest updates that will be available the next time they load the
1856 page (showing a "New content is available; please refresh." message). Showing
1857 this messages is currently left as an exercise to the developer, but as a
1858 starting point, you can make use of the logic included in [`src/registerServiceWorker.js`](src/registerServiceWorker.js), which
1859 demonstrates which service worker lifecycle events to listen for to detect each
1860 scenario, and which as a default, just logs appropriate messages to the
1863 1. By default, the generated service worker file will not intercept or cache any
1864 cross-origin traffic, like HTTP [API requests](#integrating-with-an-api-backend),
1865 images, or embeds loaded from a different domain. If you would like to use a
1866 runtime caching strategy for those requests, you can [`eject`](#npm-run-eject)
1867 and then configure the
1868 [`runtimeCaching`](https://github.com/GoogleChrome/sw-precache#runtimecaching-arrayobject)
1869 option in the `SWPrecacheWebpackPlugin` section of
1870 [`webpack.config.prod.js`](../config/webpack.config.prod.js).
1872 ### Progressive Web App Metadata
1874 The default configuration includes a web app manifest located at
1875 [`public/manifest.json`](public/manifest.json), that you can customize with
1876 details specific to your web application.
1878 When a user adds a web app to their homescreen using Chrome or Firefox on
1879 Android, the metadata in [`manifest.json`](public/manifest.json) determines what
1880 icons, names, and branding colors to use when the web app is displayed.
1881 [The Web App Manifest guide](https://developers.google.com/web/fundamentals/engage-and-retain/web-app-manifest/)
1882 provides more context about what each field means, and how your customizations
1883 will affect your users' experience.
1885 ## Analyzing the Bundle Size
1887 [Source map explorer](https://www.npmjs.com/package/source-map-explorer) analyzes
1888 JavaScript bundles using the source maps. This helps you understand where code
1889 bloat is coming from.
1891 To add Source map explorer to a Create React App project, follow these steps:
1894 npm install --save source-map-explorer
1897 Alternatively you may use `yarn`:
1900 yarn add source-map-explorer
1903 Then in `package.json`, add the following line to `scripts`:
1907 + "analyze": "source-map-explorer build/static/js/main.*",
1908 "start": "react-scripts start",
1909 "build": "react-scripts build",
1910 "test": "react-scripts test --env=jsdom",
1913 Then to analyze the bundle run the production build then run the analyze
1923 `npm run build` creates a `build` directory with a production build of your app. Set up your favorite 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.
1927 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:
1930 npm install -g serve
1934 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.
1936 Run this command to get a full list of the options available:
1944 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.
1946 Here’s a programmatic example using [Node](https://nodejs.org/) and [Express](http://expressjs.com/):
1949 const express = require('express');
1950 const path = require('path');
1951 const app = express();
1953 app.use(express.static(path.join(__dirname, 'build')));
1955 app.get('/', function (req, res) {
1956 res.sendFile(path.join(__dirname, 'build', 'index.html'));
1962 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.
1964 The `build` folder with static assets is the only output produced by Create React App.
1966 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.
1968 ### Serving Apps with Client-Side Routing
1970 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.
1972 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:
1975 app.use(express.static(path.join(__dirname, 'build')));
1977 -app.get('/', function (req, res) {
1978 +app.get('/*', function (req, res) {
1979 res.sendFile(path.join(__dirname, 'build', 'index.html'));
1983 If you’re using [Apache HTTP Server](https://httpd.apache.org/), you need to create a `.htaccess` file in the `public` folder that looks like this:
1988 RewriteCond %{REQUEST_FILENAME} !-f
1989 RewriteRule ^ index.html [QSA,L]
1992 It will get copied to the `build` folder when you run `npm run build`.
1994 If you’re using [Apache Tomcat](http://tomcat.apache.org/), you need to follow [this Stack Overflow answer](https://stackoverflow.com/a/41249464/4878474).
1996 Now requests to `/todos/42` will be handled correctly both in development and in production.
1998 On a production build, and in a browser that supports [service workers](https://developers.google.com/web/fundamentals/getting-started/primers/service-workers),
1999 the service worker will automatically handle all navigation requests, like for
2000 `/todos/42`, by serving the cached copy of your `index.html`. This
2001 service worker navigation routing can be configured or disabled by
2002 [`eject`ing](#npm-run-eject) and then modifying the
2003 [`navigateFallback`](https://github.com/GoogleChrome/sw-precache#navigatefallback-string)
2004 and [`navigateFallbackWhitelist`](https://github.com/GoogleChrome/sw-precache#navigatefallbackwhitelist-arrayregexp)
2005 options of the `SWPreachePlugin` [configuration](../config/webpack.config.prod.js).
2007 When users install your app to the homescreen of their device the default configuration will make a shortcut to `/index.html`. This may not work for client-side routers which expect the app to be served from `/`. Edit the web app manifest at [`public/manifest.json`](public/manifest.json) and change `start_url` to match the required URL scheme, for example:
2013 ### Building for Relative Paths
2015 By default, Create React App produces a build assuming your app is hosted at the server root.<br>
2016 To override this, specify the `homepage` in your `package.json`, for example:
2019 "homepage": "http://mywebsite.com/relativepath",
2022 This will let Create React App correctly infer the root path to use in the generated HTML file.
2024 **Note**: If you are using `react-router@^4`, you can root `<Link>`s using the `basename` prop on any `<Router>`.<br>
2025 More information [here](https://reacttraining.com/react-router/web/api/BrowserRouter/basename-string).<br>
2029 <BrowserRouter basename="/calendar"/>
2030 <Link to="/today"/> // renders <a href="/calendar/today">
2033 #### Serving the Same Build from Different Paths
2035 >Note: this feature is available with `react-scripts@0.9.0` and higher.
2037 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`:
2043 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.
2045 ### [Azure](https://azure.microsoft.com/)
2047 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.
2049 See [this](https://medium.com/@strid/host-create-react-app-on-azure-986bc40d5bf2#.pycfnafbg) blog post or [this](https://github.com/ulrikaugustsson/azure-appservice-static) repo for a way to use automatic deployment to Azure App Service.
2051 ### [Firebase](https://firebase.google.com/)
2053 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.
2055 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`.
2060 First, let's associate this project directory with a Firebase project.
2061 You can create multiple project aliases by running firebase use --add,
2062 but for now we'll just set up a default project.
2064 ? What Firebase project do you want to associate as default? Example app (example-app-fd690)
2068 Firebase Realtime Database Rules allow you to define how your data should be
2069 structured and when your data can be read from and written to.
2071 ? What file should be used for Database Rules? database.rules.json
2072 ✔ Database Rules for example-app-fd690 have been downloaded to database.rules.json.
2073 Future modifications to database.rules.json will update Database Rules when you run
2078 Your public directory is the folder (relative to your project directory) that
2079 will contain Hosting assets to uploaded with firebase deploy. If you
2080 have a build process for your assets, use your build's output directory.
2082 ? What do you want to use as your public directory? build
2083 ? Configure as a single-page app (rewrite all urls to /index.html)? Yes
2084 ✔ Wrote build/index.html
2086 i Writing configuration info to firebase.json...
2087 i Writing project information to .firebaserc...
2089 ✔ Firebase initialization complete!
2092 IMPORTANT: you need to set proper HTTP caching headers for `service-worker.js` file in `firebase.json` file or you will not be able to see changes after first deployment ([issue #2440](https://github.com/facebookincubator/create-react-app/issues/2440)). It should be added inside `"hosting"` key like next:
2099 {"source": "/service-worker.js", "headers": [{"key": "Cache-Control", "value": "no-cache"}]}
2104 Now, after you create a production build with `npm run build`, you can deploy it by running `firebase deploy`.
2107 === Deploying to 'example-app-fd690'...
2109 i deploying database, hosting
2110 ✔ database: rules ready to deploy.
2111 i hosting: preparing build directory for upload...
2112 Uploading: [============================== ] 75%✔ hosting: build folder uploaded successfully
2113 ✔ hosting: 8 files uploaded successfully
2114 i starting release process (may take several minutes)...
2118 Project Console: https://console.firebase.google.com/project/example-app-fd690/overview
2119 Hosting URL: https://example-app-fd690.firebaseapp.com
2122 For more information see [Add Firebase to your JavaScript Project](https://firebase.google.com/docs/web/setup).
2124 ### [GitHub Pages](https://pages.github.com/)
2126 >Note: this feature is available with `react-scripts@0.2.0` and higher.
2128 #### Step 1: Add `homepage` to `package.json`
2130 **The step below is important!**<br>
2131 **If you skip it, your app will not deploy correctly.**
2133 Open your `package.json` and add a `homepage` field for your project:
2136 "homepage": "https://myusername.github.io/my-app",
2139 or for a GitHub user page:
2142 "homepage": "https://myusername.github.io",
2145 Create React App uses the `homepage` field to determine the root URL in the built HTML file.
2147 #### Step 2: Install `gh-pages` and add `deploy` to `scripts` in `package.json`
2149 Now, whenever you run `npm run build`, you will see a cheat sheet with instructions on how to deploy to GitHub Pages.
2151 To publish it at [https://myusername.github.io/my-app](https://myusername.github.io/my-app), run:
2154 npm install --save gh-pages
2157 Alternatively you may use `yarn`:
2163 Add the following scripts in your `package.json`:
2167 + "predeploy": "npm run build",
2168 + "deploy": "gh-pages -d build",
2169 "start": "react-scripts start",
2170 "build": "react-scripts build",
2173 The `predeploy` script will run automatically before `deploy` is run.
2175 If you are deploying to a GitHub user page instead of a project page you'll need to make two
2176 additional modifications:
2178 1. First, change your repository's source branch to be any branch other than **master**.
2179 1. Additionally, tweak your `package.json` scripts to push deployments to **master**:
2182 "predeploy": "npm run build",
2183 - "deploy": "gh-pages -d build",
2184 + "deploy": "gh-pages -b master -d build",
2187 #### Step 3: Deploy the site by running `npm run deploy`
2195 #### Step 4: Ensure your project’s settings use `gh-pages`
2197 Finally, make sure **GitHub Pages** option in your GitHub project settings is set to use the `gh-pages` branch:
2199 <img src="http://i.imgur.com/HUjEr9l.png" width="500" alt="gh-pages branch setting">
2201 #### Step 5: Optionally, configure the domain
2203 You can configure a custom domain with GitHub Pages by adding a `CNAME` file to the `public/` folder.
2205 #### Notes on client-side routing
2207 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:
2209 * 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://reacttraining.com/react-router/web/api/Router) about different history implementations in React Router.
2210 * 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).
2212 ### [Heroku](https://www.heroku.com/)
2214 Use the [Heroku Buildpack for Create React App](https://github.com/mars/create-react-app-buildpack).<br>
2215 You can find instructions in [Deploying React with Zero Configuration](https://blog.heroku.com/deploying-react-with-zero-configuration).
2217 #### Resolving Heroku Deployment Errors
2219 Sometimes `npm run build` works locally but fails during deploy via Heroku. Following are the most common cases.
2221 ##### "Module not found: Error: Cannot resolve 'file' or 'directory'"
2223 If you get something like this:
2226 remote: Failed to create a production build. Reason:
2227 remote: Module not found: Error: Cannot resolve 'file' or 'directory'
2228 MyDirectory in /tmp/build_1234/src
2231 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.
2233 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.
2235 ##### "Could not find a required file."
2237 If you exclude or ignore necessary files from the package you will see a error similar this one:
2240 remote: Could not find a required file.
2241 remote: Name: `index.html`
2242 remote: Searched in: /tmp/build_a2875fc163b209225122d68916f1d4df/public
2244 remote: npm ERR! Linux 3.13.0-105-generic
2245 remote: npm ERR! argv "/tmp/build_a2875fc163b209225122d68916f1d4df/.heroku/node/bin/node" "/tmp/build_a2875fc163b209225122d68916f1d4df/.heroku/node/bin/npm" "run" "build"
2248 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`.
2250 ### [Netlify](https://www.netlify.com/)
2252 **To do a manual deploy to Netlify’s CDN:**
2255 npm install netlify-cli -g
2259 Choose `build` as the path to deploy.
2261 **To setup continuous delivery:**
2263 With this setup Netlify will build and deploy when you push to git or open a pull request:
2265 1. [Start a new netlify project](https://app.netlify.com/signup)
2266 2. Pick your Git hosting service and select your repository
2267 3. Set `yarn build` as the build command and `build` as the publish directory
2268 4. Click `Deploy site`
2270 **Support for client-side routing:**
2272 To support `pushState`, make sure to create a `public/_redirects` file with the following rewrite rules:
2278 When you build the project, Create React App will place the `public` folder contents into the build output.
2280 ### [Now](https://zeit.co/now)
2282 Now offers a zero-configuration single-command deployment. You can use `now` to deploy your app for free.
2284 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`.
2286 2. Build your app by running `npm run build`.
2288 3. Move into the build directory by running `cd build`.
2290 4. Run `now --name your-project-name` from within the build directory. You will see a **now.sh** URL in your output like this:
2293 > Ready! https://your-project-name-tpspyhtdtk.now.sh (copied to clipboard)
2296 Paste that URL into your browser when the build is complete, and you will see your deployed app.
2298 Details are available in [this article.](https://zeit.co/blog/unlimited-static)
2300 ### [S3](https://aws.amazon.com/s3) and [CloudFront](https://aws.amazon.com/cloudfront/)
2302 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 and CloudFront.
2304 ### [Surge](https://surge.sh/)
2306 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.
2308 When asked about the project path, make sure to specify the `build` folder, for example:
2311 project path: /path/to/project/build
2314 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).
2316 ## Advanced Configuration
2318 You can adjust various development and production settings by setting environment variables in your shell or with [.env](#adding-development-environment-variables-in-env).
2320 Variable | Development | Production | Usage
2321 :--- | :---: | :---: | :---
2322 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. If you need to customize the way the browser is launched, you can specify a node script instead. Any arguments passed to `npm start` will also be passed to this script, and the url where your app is served will be the last argument. Your script's file name must have the `.js` extension.
2323 HOST | :white_check_mark: | :x: | By default, the development web server binds to `localhost`. You may use this variable to specify a different host.
2324 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.
2325 HTTPS | :white_check_mark: | :x: | When set to `true`, Create React App will run the development server in `https` mode.
2326 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.
2327 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.
2328 REACT_EDITOR | :white_check_mark: | :x: | When an app crashes in development, you will see an error overlay with clickable stack trace. When you click on it, Create React App will try to determine the editor you are using based on currently running processes, and open the relevant source file. You can [send a pull request to detect your editor of choice](https://github.com/facebookincubator/create-react-app/issues/2636). Setting this environment variable overrides the automatic detection. If you do it, make sure your systems [PATH](https://en.wikipedia.org/wiki/PATH_(variable)) environment variable points to your editor’s bin folder. You can also set it to `none` to disable it completely.
2329 CHOKIDAR_USEPOLLING | :white_check_mark: | :x: | When set to `true`, the watcher runs in polling mode, as necessary inside a VM. Use this option if `npm start` isn't detecting changes.
2330 GENERATE_SOURCEMAP | :x: | :white_check_mark: | When set to `false`, source maps are not generated for a production build. This solves OOM issues on some smaller machines.
2331 NODE_PATH | :white_check_mark: | :white_check_mark: | Same as [`NODE_PATH` in Node.js](https://nodejs.org/api/modules.html#modules_loading_from_the_global_folders), but only relative folders are allowed. Can be handy for emulating a monorepo setup by setting `NODE_PATH=src`.
2335 ### `npm start` doesn’t detect changes
2337 When you save a file while `npm start` is running, the browser should refresh with the updated code.<br>
2338 If this doesn’t happen, try one of the following workarounds:
2340 * If your project is in a Dropbox folder, try moving it out.
2341 * 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.
2342 * 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 [“Adjusting Your Text Editor”](https://webpack.js.org/guides/development/#adjusting-your-text-editor).
2343 * 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).
2344 * On Linux and macOS, you might need to [tweak system settings](https://github.com/webpack/docs/wiki/troubleshooting#not-enough-watchers) to allow more watchers.
2345 * 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.
2347 If none of these solutions help please leave a comment [in this thread](https://github.com/facebookincubator/create-react-app/issues/659).
2349 ### `npm test` hangs on macOS Sierra
2351 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).
2353 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:
2355 * [facebook/jest#1767](https://github.com/facebook/jest/issues/1767)
2356 * [facebook/watchman#358](https://github.com/facebook/watchman/issues/358)
2357 * [ember-cli/ember-cli#6259](https://github.com/ember-cli/ember-cli/issues/6259)
2359 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:
2362 watchman shutdown-server
2364 brew reinstall watchman
2367 You can find [other installation methods](https://facebook.github.io/watchman/docs/install.html#build-install) on the Watchman documentation page.
2369 If this still doesn’t help, try running `launchctl unload -F ~/Library/LaunchAgents/com.github.facebook.watchman.plist`.
2371 There are also reports that *uninstalling* Watchman fixes the issue. So if nothing else helps, remove it from your system and try again.
2373 ### `npm run build` exits too early
2375 It is reported that `npm run build` can fail on machines with limited memory and no swap space, which is common in cloud environments. Even with small projects this command can increase RAM usage in your system by hundreds of megabytes, so if you have less than 1 GB of available memory your build is likely to fail with the following message:
2377 > The build failed because the process exited too early. This probably means the system ran out of memory or someone called `kill -9` on the process.
2379 If you are completely sure that you didn't terminate the process, consider [adding some swap space](https://www.digitalocean.com/community/tutorials/how-to-add-swap-on-ubuntu-14-04) to the machine you’re building on, or build the project locally.
2381 ### `npm run build` fails on Heroku
2383 This may be a problem with case sensitive filenames.
2384 Please refer to [this section](#resolving-heroku-deployment-errors).
2386 ### Moment.js locales are missing
2388 If you use a [Moment.js](https://momentjs.com/), you might notice that only the English locale is available by default. This is because the locale files are large, and you probably only need a subset of [all the locales provided by Moment.js](https://momentjs.com/#multiple-locale-support).
2390 To add a specific Moment.js locale to your bundle, you need to import it explicitly.<br>
2394 import moment from 'moment';
2395 import 'moment/locale/fr';
2398 If import multiple locales this way, you can later switch between them by calling `moment.locale()` with the locale name:
2401 import moment from 'moment';
2402 import 'moment/locale/fr';
2403 import 'moment/locale/es';
2407 moment.locale('fr');
2410 This will only work for locales that have been explicitly imported before.
2412 ### `npm run build` fails to minify
2414 Some third-party packages don't compile their code to ES5 before publishing to npm. This often causes problems in the ecosystem because neither browsers (except for most modern versions) nor some tools currently support all ES6 features. We recommend to publish code on npm as ES5 at least for a few more years.
2419 1. Open an issue on the dependency's issue tracker and ask that the package be published pre-compiled.
2420 * Note: Create React App can consume both CommonJS and ES modules. For Node.js compatibility, it is recommended that the main entry point is CommonJS. However, they can optionally provide an ES module entry point with the `module` field in `package.json`. Note that **even if a library provides an ES Modules version, it should still precompile other ES6 features to ES5 if it intends to support older browsers**.
2422 2. Fork the package and publish a corrected version yourself.
2424 3. If the dependency is small enough, copy it to your `src/` folder and treat it as application code.
2426 In the future, we might start automatically compiling incompatible third-party modules, but it is not currently supported. This approach would also slow down the production builds.
2428 ## Alternatives to Ejecting
2430 [Ejecting](#npm-run-eject) lets you customize anything, but from that point on you have to maintain the configuration and scripts yourself. This can be daunting if you have many similar projects. In such cases instead of ejecting we recommend to *fork* `react-scripts` and any other packages you need. [This article](https://auth0.com/blog/how-to-configure-create-react-app/) dives into how to do it in depth. You can find more discussion in [this issue](https://github.com/facebookincubator/create-react-app/issues/682).
2432 ## Something Missing?
2434 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)