Installation

React is flexible and can be used in a variety of projects. You can create new apps with it, but you can also gradually introduce it into an existing codebase without doing a rewrite.

Trying Out React

If you're just interested in playing around with React, you can use CodePen. Try starting from this Hello World example code. You don't need to install anything; you can just modify the code and see if it works.

If you prefer to use your own text editor, you can also download this HTML file, edit it, and open it from the local filesystem in your browser. It does a slow runtime code transformation, so don't use it in production.

Creating a Single Page Application

Create React App is the best way to start building a new React single page application. It sets up your development environment so that you can use the latest JavaScript features, provides a nice developer experience, and optimizes your app for production.

npm install -g create-react-app
create-react-app hello-world
cd hello-world
npm start

Create React App doesn't handle backend logic or databases; it just creates a frontend build pipeline, so you can use it with any backend you want. It uses webpack, Babel and ESLint under the hood, but configures them for you.

Adding React to an Existing Application

You don't need to rewrite your app to start using React.

We recommend adding React to a small part of your application, such as an individual widget, so you can see if it works well for your use case.

While React can be used without a build pipeline, we recommend setting it up so you can be more productive. A modern build pipeline typically consists of:

• A package manager, such as Yarn or npm. It lets you take advantage of a vast ecosystem of third-party packages, and easily install or update them.
• A bundler, such as webpack or Browserify. It lets you write modular code and bundle it together into small packages to optimize load time.
• A compiler such as Babel. It lets you write modern JavaScript code that still works in older browsers.

Installing React

We recommend using Yarn or npm for managing front-end dependencies. If you're new to package managers, the Yarn documentation is a good place to get started.

To install React with Yarn, run:

yarn init
yarn add react react-dom

To install React with npm, run:

npm init
npm install --save react react-dom

Both Yarn and npm download packages from the npm registry.

Enabling ES6 and JSX

We recommend using React with Babel to let you use ES6 and JSX in your JavaScript code. ES6 is a set of modern JavaScript features that make development easier, and JSX is an extension to the JavaScript language that works nicely with React.

The Babel setup instructions explain how to configure Babel in many different build environments. Make sure you install babel-preset-react and babel-preset-es2015 and enable them in your .babelrc configuration, and you're good to go.

Hello World with ES6 and JSX

We recommend using a bundler like webpack or Browserify so you can write modular code and bundle it together into small packages to optimize load time.

The smallest React example looks like this:

import React from 'react';
import ReactDOM from 'react-dom';

ReactDOM.render(
  <h1>Hello, world!</h1>,
  document.getElementById('root')
);

This code renders into a DOM element with the id of root so you need <div id="root"></div> somewhere in your HTML file.

Similarly, you can render a React component inside a DOM element somewhere inside your existing app written with any other JavaScript UI library.

Development and Production Versions

By default, React includes many helpful warnings. These warnings are very useful in development. However, they make React larger and slower so you should make sure to use the production version when you deploy the app.

Brunch

To create an optimized production build with Brunch, just add the -p flag to the build command. See the Brunch docs for more details.

Browserify

Run Browserify with NODE_ENV environment variable set to production and use UglifyJS as the last build step so that development-only code gets stripped out.

Create React App

If you use Create React App, npm run build will create an optimized build of your app in the build folder.

Rollup

Use rollup-plugin-replace plugin together with rollup-plugin-commonjs (in that order) to remove development-only code. See this gist for a complete setup example.

Webpack

Include both DefinePlugin and UglifyJsPlugin into your production Webpack configuration as described in this guide.

Using a CDN

If you don't want to use npm to manage client packages, the react and react-dom npm packages also provide single-file distributions in dist folders, which are hosted on a CDN:

<script src="https://unpkg.com/react@15/dist/react.js"></script>
<script src="https://unpkg.com/react-dom@15/dist/react-dom.js"></script>

The versions above are only meant for development, and are not suitable for production. Minified and optimized production versions of React are available at:

<script src="https://unpkg.com/react@15/dist/react.min.js"></script>
<script src="https://unpkg.com/react-dom@15/dist/react-dom.min.js"></script>

To load a specific version of react and react-dom, replace 15 with the version number.

If you use Bower, React is available via the react package.