react-starter-kit

This project aims to be an opinionated starter kit for building UI applications using React.

Installation

Clone the repo and install the depencies

git clone [email protected]:serviceslabs/react-starter.git --starter react-starter-kit your_project_name
cd your-project-name
yarn install

After installing all the dependencies and locking them as yarn.lock you should be ready to start you server

yarn start

Features

Core

• react (15.4)
• react-Router (4.0)
• styled-Components
• redux
• redux-saga
• axios

UI Theme

• material-ui

Testing

• jest
• enzyme

Productivity

• webpack
• eslint
• babel
• redux-logger

Available Scripts

In the project directory, you can run:

npm start

Runs the app in the development mode.
Open http://localhost:3000 to view it in the browser.

The page will reload if you make edits.
You will also see any lint errors in the console.

npm test

Launches the test runner in the interactive watch mode.
See the section about running tests for more information.

npm ci

This will run all the test files along with coverage enabled. Good to run in it on CI to certify a build. The coverage threshold has been set to 50% for now

npm run build

Builds the app for production to the build folder.
It correctly bundles React in production mode and optimizes the build for the best performance.

The build is minified and the filenames include the hashes.
Your app is ready to be deployed!

See the section about deployment for more information.

Table of Contents

• Updating to New Releases
• Folder Structure
• Supported Language Features and Polyfills
• Syntax Highlighting in the Editor
• Displaying Lint Output in the Editor
• Debugging in the Editor
• Changing the Page <title>
• Installing a Dependency
• Importing a Component
• Adding Styles
• Adding a CSS Preprocessor (Sass, Less etc.)
• Adding Images, Fonts, and Files
• Using the public Folder
  • Changing the HTML
  • Adding Assets Outside of the Module System
  • When to Use the public Folder
• Adding Flow
• Adding Custom Environment Variables
  • Referencing Environment Variables in the HTML
  • Adding Temporary Environment Variables In Your Shell
  • Adding Development Environment Variables In .env
• Can I Use Decorators?
• Integrating with an API Backend
  • Node
  • Ruby on Rails
• Proxying API Requests in Development
• Using HTTPS in Development
• Generating Dynamic <meta> Tags on the Server
• Pre-Rendering into Static HTML Files
• Injecting Data from the Server into the Page
• Running Tests
  • Filename Conventions
  • Command Line Interface
  • Version Control Integration
  • Writing Tests
  • Testing Components
  • Using Third Party Assertion Libraries
  • Initializing Test Environment
  • Focusing and Excluding Tests
  • Coverage Reporting
  • Continuous Integration
  • Disabling jsdom
  • Snapshot Testing
  • Editor Integration
• Developing Components in Isolation
• Making a Progressive Web App
• Deployment
  • Static Server
  • Other Solutions
  • S3 and CloudFront
  • Surge
• Advanced Configuration

Updating to New Releases

You can always pull the changes from the react-starter-kit upstream

git pull react-starter-kit master

Any updates changes in the starter kit repo should be available in your project now

Remember to run yarn install to update any new dependencies

Folder Structure

After creation, your project should look like this:

my-app/
  README.md
  node_modules/
  package.json
  public/
    index.html
    favicon.ico
  src/
     components/
     	Home.js
     images/
     	...
     layout/
     	app.js
     styles/
     	StyledComponents.js
     index.js
     routes.js
  tests/
  	App.test.json

For the project to build, these files must exist with exact filenames:

• public/index.html is the page template;
• src/index.js is the JavaScript entry point.

You can delete or rename the other files.

You may create subdirectories inside src. For faster rebuilds, only files inside src are processed by Webpack.
You need to put any JS and CSS files inside src, or Webpack won’t see them.

Only files inside public can be used from public/index.html.
Read instructions below for using assets from JavaScript and HTML.

You can, however, create more top-level directories.
They will not be included in the production build so you can use them for things like documentation.

Supported Language Features and Polyfills

This project supports a superset of the latest JavaScript standard.
In addition to ES6 syntax features, it also supports:

• Exponentiation Operator (ES2016).
• Async/await (ES2017).
• Object Rest/Spread Properties (stage 3 proposal).
• Class Fields and Static Properties (stage 2 proposal).
• JSX and Flow syntax.

Note that the project only includes a few ES6 polyfills:

• Object.assign() via object-assign.
• Promise via promise.
• fetch() via whatwg-fetch.

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.

Syntax Highlighting in the Editor

To configure the syntax highlighting in your favorite text editor, head to the relevant Babel documentation page and follow the instructions. Some of the most popular editors are covered.

Displaying Lint Output in the Editor

Note: this feature is available with [email protected] and higher.
It also only works with npm 3 or higher.

Some editors, including Sublime Text, Atom, and Visual Studio Code, provide plugins for ESLint.

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.

You would need to install an ESLint plugin for your editor first. Then, add a file called .eslintrc to the project root:

{
  "extends": "react-app"
}

Now your editor should report the linting warnings.

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.

If you want to enforce a coding style for your project, consider using Prettier instead of ESLint style rules.

Debugging in the Editor

This feature is currently only supported by Visual Studio Code editor.

Visual Studio Code supports live-editing and debugging out of the box with Create React App. This enables you as a developer to write and debug your React code without leaving the editor, and most importantly it enables you to have a continuous development workflow, where context switching is minimal, as you don’t have to switch between tools.

You would need to have the latest version of VS Code and VS Code Chrome Debugger Extension installed.

Then add the block below to your launch.json file and put it inside the .vscode folder in your app’s root directory.

{
  "version": "0.2.0",
  "configurations": [{
    "name": "Chrome",
    "type": "chrome",
    "request": "launch",
    "url": "http://localhost:3000",
    "webRoot": "${workspaceRoot}/src",
    "userDataDir": "${workspaceRoot}/.vscode/chrome",
    "sourceMapPathOverrides": {
      "webpack:///src/*": "${webRoot}/*"
    }
  }]
}

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.

Changing the Page <title>

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.

Note that normally you wouldn’t edit files in the public folder very often. For example, adding a stylesheet is done without touching the HTML.

If you need to dynamically update the page title based on the content, you can use the browser document.title API. For more complex scenarios when you want to change the title from React components, you can use React Helmet, a third party library.

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. Alternatively, you can pre-build each page as a static HTML file which then loads the JavaScript bundle, which is covered here.

Installing a Dependency

The generated project basic dependencies to get you started. It also includes a set of scripts used by Create React App as a development dependency. You may install other dependencies (for example, React-Material) with yarn:

yarn add <library-name>

Importing a Component

This project setup supports ES6 modules thanks to Babel.
While you can still use require() and module.exports, we encourage you to use import and export instead.

For example:

Button.js

import React, { Component } from 'react';

class Button extends Component {
  render() {
    // ...
  }
}

export default Button; // Don’t forget to use export default!

DangerButton.js

import React, { Component } from 'react';
import Button from './Button'; // Import a component from another file

class DangerButton extends Component {
  render() {
    return <Button color="red" />;
  }
}

export default DangerButton;

Be aware of the difference between default and named exports. It is a common source of mistakes.

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'.

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.

Learn more about ES6 modules:

• When to use the curly braces?
• Exploring ES6: Modules
• Understanding ES6: Modules

Adding Styles

You can add your own custom CSS stylesheets and use them like below:

Button.css

.Button {
  padding: 20px;
}

Button.js

import React, { Component } from 'react';
import './Button.css'; // Tell Webpack that Button.js uses these styles

class Button extends Component {
  render() {
    // You can use them as regular CSS styles
    return <div className="Button" />;
  }
}

But, we recommend that you use styled-components that uses css-in-js for styling the components. A short example below:

import styled from 'styled-components';

// Create a <Title> react component that renders an <h1> which is
// centered, palevioletred and sized at 1.5em
const Title = styled.h1`
  font-size: 1.5em;
  text-align: center;
  color: palevioletred;
`

// Create a <Wrapper> react component that renders a <section> with
// some padding and a papayawhip background
const Wrapper = styled.section`
  padding: 4em;
  background: papayawhip;
`

You render them like so:

// Use them like any other React component – except they're styled!
<Wrapper>
  <Title>Hello World, this is my first styled component!</Title>
</Wrapper>

Adding Images, Fonts, and Files

With Webpack, using static assets like images and fonts works similarly to CSS.

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.

To reduce the number of requests to the server, importing images that are less than 10,000 bytes returns a data URI instead of a path. This applies to the following file extensions: bmp, gif, jpg, jpeg, and png. SVG files are excluded due to #1153.

Here is an example:

import React from 'react';
import logo from './logo.png'; // Tell Webpack this JS file uses this image

console.log(logo); // /logo.84287d09.png

function Header() {
  // Import result is the URL of your image
  return <img src={logo} alt="Logo" />;
}

export default Header;

This ensures that when the project is built, Webpack will correctly move the images into the build folder, and provide us with correct paths.

This works in CSS too:

.Logo {
  background-image: url(./logo.png);
}

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.

Please be advised that this is also a custom feature of Webpack.

It is not required for React but many people enjoy it (and React Native uses a similar mechanism for images).
An alternative way of handling static assets is described in the next section.

Using the public Folder

Note: this feature is available with [email protected] and higher.

Changing the HTML

The public folder contains the HTML file so you can tweak it, for example, to set the page title. The <script> tag with the compiled code will be added to it automatically during the build process.

Adding Assets Outside of the Module System

You can also add other assets to the public folder.

Note that we normally encourage you to import assets in JavaScript files instead. For example, see the sections on adding a stylesheet and adding images and fonts. This mechanism provides a number of benefits:

• Scripts and stylesheets get minified and bundled together to avoid extra network requests.
• Missing files cause compilation errors instead of 404 errors for your users.
• Result filenames include content hashes so you don’t need to worry about browsers caching their old versions.

However there is an escape hatch that you can use to add an asset outside of the module system.

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.

Inside index.html, you can use it like this:

<link rel="shortcut icon" href="%PUBLIC_URL%/favicon.ico">

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.

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.

In JavaScript code, you can use process.env.PUBLIC_URL for similar purposes:

render() {
  // Note: this is an escape hatch and should be used sparingly!
  // Normally we recommend using `import` for getting asset URLs
  // as described in “Adding Images and Fonts” above this section.
  return <img src={process.env.PUBLIC_URL + '/img/logo.png'} />;
}

Keep in mind the downsides of this approach:

• None of the files in public folder get post-processed or minified.
• Missing files will not be called at compilation time, and will cause 404 errors for your users.
• Result filenames won’t include content hashes so you’ll need to add query arguments or rename them every time they change.

When to Use the public Folder

Normally we recommend importing stylesheets, images, and fonts from JavaScript. The public folder is useful as a workaround for a number of less common cases:

• You need a file with a specific name in the build output, such as manifest.webmanifest.
• You have thousands of images and need to dynamically reference their paths.
• You want to include a small script like pace.js outside of the bundled code.
• Some library may be incompatible with Webpack and you have no other option but to include it as a <script> tag.

Note that if you add a <script> that declares global variables, you also need to read the next section on using them.

Adding Flow

Flow is a static type checker that helps you write code with fewer bugs. Check out this introduction to using static types in JavaScript if you are new to this concept.

Recent versions of Flow work with Create React App projects out of the box.

To add Flow to a Create React App project, follow these steps:

1. Run npm install --save-dev flow-bin (or yarn add --dev flow-bin).
2. Add "flow": "flow" to the scripts section of your package.json.
3. Run npm run flow -- init (or yarn flow -- init) to create a .flowconfig file in the root directory.
4. Add // @flow to any files you want to type check (for example, to src/app.js).

Now you can run npm run flow (or yarn flow) to check the files for type errors. You can optionally use an IDE like Nuclide for a better integrated experience. In the future we plan to integrate it into Create React App even more closely.

To learn more about Flow, check out its documentation.

Adding Custom Environment Variables

Note: this feature is available with [email protected] and higher.

Your project can consume variables declared in your environment as if they were declared locally in your JS files. By default you will have NODE_ENV defined for you, and any other environment variables starting with REACT_APP_.

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. Alternatively you can rebuild the app on the server anytime you change them.

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. Changing any environment variables will require you to restart the development server if it is running.

These environment variables will be defined for you on process.env. For example, having an environment variable named REACT_APP_SECRET_CODE will be exposed in your JS as process.env.REACT_APP_SECRET_CODE.

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.

These environment variables can be useful for displaying information conditionally based on where the project is deployed or consuming sensitive data that lives outside of version control.

First, you need to have environment variables defined. For example, let’s say you wanted to consume a secret defined in the environment inside a <form>:

render() {
  return (
    <div>
      <small>You are running this application in <b>{process.env.NODE_ENV}</b> mode.</small>
      <form>
        <input type="hidden" defaultValue={process.env.REACT_APP_SECRET_CODE} />
      </form>
    </div>
  );
}

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.

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:

<div>
  <small>You are running this application in <b>development</b> mode.</small>
  <form>
    <input type="hidden" value="abcdef" />
  </form>
</div>

The above form is looking for a variable called REACT_APP_SECRET_CODE from the environment. In order to consume this value, we need to have it defined in the environment. This can be done using two ways: either in your shell or in a .env file. Both of these ways are described in the next few sections.

Having access to the NODE_ENV is also useful for performing actions conditionally:

if (process.env.NODE_ENV !== 'production') {
  analytics.disable();
}

When you compile the app with npm run build, the minification step will strip out this condition, and the resulting bundle will be smaller.

Referencing Environment Variables in the HTML

Note: this feature is available with [email protected] and higher.

You can also access the environment variables starting with REACT_APP_ in the public/index.html. For example:

<title>%REACT_APP_WEBSITE_NAME%</title>

Note that the caveats from the above section apply:

• Apart from a few built-in variables (NODE_ENV and PUBLIC_URL), variable names must start with REACT_APP_ to work.
• The environment variables are injected at build time. If you need to inject them at runtime, follow this approach instead.

Adding Temporary Environment Variables In Your Shell

Defining environment variables can vary between OSes. It’s also important to know that this manner is temporary for the life of the shell session.

Windows (cmd.exe)

set REACT_APP_SECRET_CODE=abcdef&&npm start

(Note: the lack of whitespace is intentional.)

Linux, macOS (Bash)

REACT_APP_SECRET_CODE=abcdef npm start

Adding Development Environment Variables In .env

Note: this feature is available with [email protected] and higher.

To define permanent environment variables, create a file called .env in the root of your project:

REACT_APP_SECRET_CODE=abcdef

These variables will act as the defaults if the machine does not explicitly set them.
Please refer to the dotenv documentation for more details.

Note: If you are defining environment variables for development, your CI and/or hosting platform will most likely need these defined as well. Consult their documentation how to do this. For example, see the documentation for Travis CI or Heroku.

Can I Use Decorators?

Many popular libraries use decorators in their documentation.
Create React App doesn’t support decorator syntax at the moment because:

• It is an experimental proposal and is subject to change.
• The current specification version is not officially supported by Babel.
• If the specification changes, we won’t be able to write a codemod because we don’t use them internally at Facebook.

However in many cases you can rewrite decorator-based code without decorators just as fine.
Please refer to these two threads for reference:

• #214
• #411

Create React App will add decorator support when the specification advances to a stable stage.

Integrating with an API Backend

These tutorials will help you to integrate your app with an API backend running on another port, using fetch() to access it.

Node

Check out this tutorial. You can find the companion GitHub repository here.

Ruby on Rails

Check out this tutorial. You can find the companion GitHub repository here.

Proxying API Requests in Development

Note: this feature is available with [email protected] and higher.

People often serve the front-end React app from the same host and port as their backend implementation.
For example, a production setup might look like this after the app is deployed:

/             - static server returns index.html with React app
/todos        - static server returns index.html with React app
/api/todos    - server handles any /api/* requests using the backend implementation

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.

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:

  "proxy": "http://localhost:4000",

This way, when you fetch('/api/todos') in development, the development server will recognize that it’s not a static asset, and will proxy your request to http://localhost:4000/api/todos as a fallback. The development server will only attempt to send requests without a text/html accept header to the proxy.

Conveniently, this avoids CORS issues and error messages like this in development:

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.

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.

The proxy option supports HTTP, HTTPS and WebSocket connections.
If the proxy option is not flexible enough for you, alternatively you can:

• Enable CORS on your server (here’s how to do it for Express).
• Use environment variables to inject the right server host and port into your app.

Using HTTPS in Development

Note: this feature is available with [email protected] and higher.

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 to proxy requests to an API server when that API server is itself serving HTTPS.

To do this, set the HTTPS environment variable to true, then start the dev server as usual with npm start:

Windows (cmd.exe)

set HTTPS=true&&npm start

(Note: the lack of whitespace is intentional.)

Linux, macOS (Bash)

HTTPS=true npm start

Note that the server will use a self-signed certificate, so your web browser will almost definitely display a warning upon accessing the page.

Generating Dynamic <meta> Tags on the Server

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:

<!doctype html>
<html lang="en">
  <head>
    <meta property="og:title" content="__OG_TITLE__">
    <meta property="og:description" content="__OG_DESCRIPTION__">

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!

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.

Pre-Rendering into Static HTML Files

If you’re hosting your build with a static hosting provider you can use react-snapshot to generate HTML pages for each route, or relative link, in your application. These pages will then seamlessly become active, or “hydrated”, when the JavaScript bundle has loaded.

There are also opportunities to use this outside of static hosting, to take the pressure off the server when generating and caching routes.

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.

You can read more about zero-configuration pre-rendering (also called snapshotting) here.

Injecting Data from the Server into the Page

Similarly to the previous section, you can leave some placeholders in the HTML that inject global variables, for example:

<!doctype html>
<html lang="en">
  <head>
    <script>
      window.SERVER_DATA = __SERVER_DATA__;
    </script>

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 as it makes your app vulnerable to XSS attacks.

Running Tests

Note: this feature is available with [email protected] and higher.
Read the migration guide to learn how to enable it in older projects!

Create React App uses Jest as its test runner. To prepare for this integration, we did a major revamp of Jest so if you heard bad things about it years ago, give it another try.

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.

While Jest provides browser globals such as window thanks to 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.

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.

Filename Conventions

Jest will look for test files with any of the following popular naming conventions:

• Files with .js suffix in __tests__ folders.
• Files with .test.json suffix.
• Files with .spec.js suffix.

The .test.json / .spec.js files (or the __tests__ folders) can be located at any depth under the src top level folder.

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.json 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.

Command Line Interface

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.

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:

Version Control Integration

By default, when you run npm test, Jest will only run the tests related to files changed since the last commit. This is an optimization designed to make your tests runs fast regardless of how many tests you have. However it assumes that you don’t often commit the code that doesn’t pass the tests.

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.

Jest will always run all tests on a continuous integration server or if the project is not inside a Git or Mercurial repository.

Writing Tests

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.

Jest provides a built-in expect() global function for making assertions. A basic test could look like this:

import sum from './sum';

it('sums numbers', () => {
  expect(sum(1, 2)).toEqual(3);
  expect(sum(2, 2)).toEqual(4);
});

All expect() matchers supported by Jest are extensively documented here.
You can also use jest.fn() and expect(fn).toBeCalled() to create “spies” or mock functions.

Testing Components

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.

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:

import React from 'react';
import ReactDOM from 'react-dom';
import App from './App';

it('renders without crashing', () => {
  const div = document.createElement('div');
  ReactDOM.render(<App />, div);
});

This test mounts a component and makes sure that it didn’t throw during rendering. Tests like this provide a lot value with very little effort so they are great as a starting point, and this is the test you will find in src/App.test.json.

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.

If you’d like to test components in isolation from the child components they render, we recommend using shallow() rendering API from Enzyme. You can write a smoke test with it too:

npm install --save-dev enzyme react-test-renderer

import React from 'react';
import { shallow } from 'enzyme';
import App from './App';

it('renders without crashing', () => {
  shallow(<App />);
});

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(), and you can also use it for testing state changes and component lifecycle.

You can read the Enzyme documentation 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.

Here is an example from Enzyme documentation that asserts specific output, rewritten to use Jest matchers:

import React from 'react';
import { shallow } from 'enzyme';
import App from './App';

it('renders welcome message', () => {
  const wrapper = shallow(<App />);
  const welcome = <h2>Welcome to React</h2>;
  // expect(wrapper.contains(welcome)).to.equal(true);
  expect(wrapper.contains(welcome)).toEqual(true);
});

All Jest matchers are extensively documented here.
Nevertheless you can use a third-party assertion library like Chai if you want to, as described below.

Additionally, you might find jest-enzyme helpful to simplify your tests with readable matchers. The above contains code can be written simpler with jest-enzyme.

expect(wrapper).toContainReact(welcome)

To setup jest-enzyme with Create React App, follow the instructions for initializing your test environment to import jest-enzyme. Note that currently only version 2.x is compatible with Create React App.

npm install --save-dev [email protected]

// src/setupTests.js
import 'jest-enzyme';

Using Third Party Assertion Libraries

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, and we’ll fix them. We intend to keep making them better for React, supporting, for example, pretty-printing React elements as JSX.

However, if you are used to other libraries, such as Chai and Sinon, or if you have existing code using them that you’d like to port over, you can import them normally like this:

import sinon from 'sinon';
import { expect } from 'chai';

and then use them in your tests like you normally do.

Initializing Test Environment

Note: this feature is available with [email protected] and higher.

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.

For example:

src/setupTests.js

const localStorageMock = {
  getItem: jest.fn(),
  setItem: jest.fn(),
  clear: jest.fn()
};
global.localStorage = localStorageMock

Focusing and Excluding Tests

You can replace it() with xit() to temporarily exclude a test from being executed.
Similarly, fit() lets you focus on a specific test without running any other tests.

Coverage Reporting

Jest has an integrated coverage reporter that works well with ES6 and requires no configuration.
Run npm test -- --coverage (note extra -- in the middle) to include a coverage report like this:

Note that tests run much slower with coverage so it is recommended to run it separately from your normal workflow.

Continuous Integration

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.

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.

Popular CI servers already set the environment variable CI by default but you can do this yourself too:

On CI servers

Travis CI

1. Following the Travis Getting started guide for syncing your GitHub repository with Travis. You may need to initialize some settings manually in your profile page.
2. Add a .travis.yml file to your git repository.

language: node_js
node_js:
  - 4
  - 6
cache:
  directories:
    - node_modules
script:
  - npm test
  - npm run build

1. Trigger your first build with a git push.
2. Customize your Travis CI Build if needed.

On your own environment

Windows (cmd.exe)

set CI=true&&npm test

set CI=true&&npm run build

(Note: the lack of whitespace is intentional.)

Linux, macOS (Bash)

CI=true npm test

CI=true npm run build

The test command will force Jest to run tests once instead of launching the watcher.

If you find yourself doing this often in development, please file an issue 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.

The build command will check for linter warnings and fail if any are found.

Disabling jsdom

By default, the package.json of the generated project looks like this:

  // ...
  "scripts": {
    // ...
    "test": "react-scripts test --env=jsdom"
  }

If you know that none of your tests depend on jsdom, you can safely remove --env=jsdom, and your tests will run faster.
To help you make up your mind, here is a list of APIs that need jsdom:

• Any browser globals like window and document
• ReactDOM.render()
• TestUtils.renderIntoDocument() (a shortcut for the above)
• mount() in Enzyme

In contrast, jsdom is not needed for the following APIs:

• TestUtils.createRenderer() (shallow rendering)
• shallow() in Enzyme

Finally, jsdom is also not needed for snapshot testing.

Snapshot Testing

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.

Editor Integration

If you use Visual Studio Code, there is a Jest extension 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.

Developing Components in Isolation

Usually, in an app, you have a lot of UI components, and each of them has many different states. For an example, a simple button component could have following states:

• With a text label.
• With an emoji.
• In the disabled mode.

Usually, it’s hard to see these states without running a sample app or some examples.

Create React App doesn’t include any tools for this by default, but you can easily add React Storybook to your project. It is a third-party tool that lets you develop components and see all their states in isolation from your app.

You can also deploy your Storybook as a static app. This way, everyone in your team can view and review different states of UI components without starting a backend server or creating an account in your app.

Here’s how to setup your app with Storybook:

First, install the following npm package globally:

npm install -g getstorybook

Then, run the following command inside your app’s directory:

getstorybook

After that, follow the instructions on the screen.

Learn more about React Storybook:

• Screencast: Getting Started with React Storybook
• GitHub Repo
• Documentation
• Snapshot Testing with React Storybook

Making a Progressive Web App

You can turn your React app into a Progressive Web App by following the steps in this repository.

Deployment

npm run build creates a build directory with a production build of your app. Set up your favourite HTTP server so that a visitor to your site is served index.html, and requests to static paths like /static/js/main.<hash>.js are served with the contents of the /static/js/main.<hash>.js file.

Static Server

For environments using Node, the easiest way to handle this would be to install serve and let it handle the rest:

npm install -g serve
serve -s build

The last command shown above will serve your static site on the port 5000. Like many of serve’s internal settings, the port can be adjusted using the -p or --port flags.

Run this command to get a full list of the options available:

serve -h

Other Solutions

S3 and CloudFront

See this blog post on how to deploy your React app to Amazon Web Services S3 and CloudFront.

Surge

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.

When asked about the project path, make sure to specify the build folder, for example:

       project path: /path/to/project/build

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.

Advanced Configuration

You can adjust various development and production settings by setting environment variables in your shell or with .env.

](https://github.com/facebookincubator/create-react-app/edit/master/packages/react-scripts/template/README.md)