Multi-platform setup

Please read the setup guide first. If you have an existing React Native application, there are more areas that require attention and customization before most web bundlers can consume the non-standard JavaScript in packages produced by the React Native ecosystem. Additionally, 3rd party React Native packages with web support are listed in the React Native Directory.

If you are interested in making a multi-platform app it is strongly recommended that you use Expo (or learn from the source code for the Web integration). Expo includes web support and takes care of all the configuration work required.

Web-specific code

Minor platform differences can use the Platform module.

import { Platform } from 'react-native';

const styles = StyleSheet.create({
  height: (Platform.OS === 'web') ? 200 : 100,
});

More significant platform differences should use platform-specific files (see the webpack configuration below for resolving *.web.js files):

For example, with the following files in your project:

MyComponent.android.js
MyComponent.ios.js
MyComponent.web.js

And the following import:

import MyComponent from './MyComponent';

React Native will automatically import the correct variant for each specific target platform.

Compiling and Bundling

What follows is only an example of a basic way to package a Web app using webpack and Babel. (Metro is the React Native bundler with undocumented web support.)

Install webpack-related dependencies, for example:

npm install --save-dev babel-loader url-loader webpack webpack-cli webpack-dev-server

React Native’s Babel preset rewrites ES modules to CommonJS modules, preventing bundlers from automatically performing “tree-shaking” to remove unused modules from your web app build. To help with this, you can install the following Babel plugin:

npm install --save-dev babel-plugin-react-native-web

Create a web/webpack.config.js file:

// web/webpack.config.js

const path = require('path');
const webpack = require('webpack');

const appDirectory = path.resolve(__dirname, '../');

// This is needed for webpack to compile JavaScript.
// Many OSS React Native packages are not compiled to ES5 before being
// published. If you depend on uncompiled packages they may cause webpack build
// errors. To fix this webpack can be configured to compile to the necessary
// `node_module`.
const babelLoaderConfiguration = {
  test: /\.js$/,
  // Add every directory that needs to be compiled by Babel during the build.
  include: [
    path.resolve(appDirectory, 'index.web.js'),
    path.resolve(appDirectory, 'src'),
    path.resolve(appDirectory, 'node_modules/react-native-uncompiled')
  ],
  use: {
    loader: 'babel-loader',
    options: {
      cacheDirectory: true,
      // The 'metro-react-native-babel-preset' preset is recommended to match React Native's packager
      presets: ['module:metro-react-native-babel-preset'],
      // Re-write paths to import only the modules needed by the app
      plugins: ['react-native-web']
    }
  }
};

// This is needed for webpack to import static images in JavaScript files.
const imageLoaderConfiguration = {
  test: /\.(gif|jpe?g|png|svg)$/,
  use: {
    loader: 'url-loader',
    options: {
      name: '[name].[ext]',
      esModule: false,
    }
  }
};

module.exports = {
  entry: [
    // load any web API polyfills
    // path.resolve(appDirectory, 'polyfills-web.js'),
    // your web-specific entry file
    path.resolve(appDirectory, 'index.web.js')
  ],

  // configures where the build ends up
  output: {
    filename: 'bundle.web.js',
    path: path.resolve(appDirectory, 'dist')
  },

  // ...the rest of your config

  module: {
    rules: [
      babelLoaderConfiguration,
      imageLoaderConfiguration
    ]
  },

  resolve: {
    // This will only alias the exact import "react-native"
    alias: {
      'react-native$': 'react-native-web'
    },
    // If you're working on a multi-platform React Native app, web-specific
    // module implementations should be written in files using the extension
    // `.web.js`.
    extensions: [ '.web.js', '.js' ]
  }
}

To run in development from the root of your application:

./node_modules/.bin/webpack-dev-server -d --config ./web/webpack.config.js --inline --hot --colors

To build for production:

./node_modules/.bin/webpack -p --config ./web/webpack.config.js

Please refer to the Webpack documentation for more information on configuration.