This guide will show you how to use Expo web with a native-only React Native project bootstrapped with @react-native-community/cli. You can run web without installing any of the Expo SDK using the expo-cli, we'll start with this then you can optionally add more Expo features later.

In order to start a zero-config web project, you'll need to install the Expo CLI: npm install -g expo-cli
Install the minimum packages: yarn add react-native-web react-dom.
Add basic web support to the entry file (index.js):

import {AppRegistry, Platform} from 'react-native';
import App from './App';

AppRegistry.registerComponent('main', () => App);

if (Platform.OS === 'web') {
  const rootTag = document.getElementById('root');
  AppRegistry.runApplication('main', {rootTag});
}

You'll need to modify the app.json to be universal like so:

{
    "name": "reactnativeinitdemo",
    "displayName": "React Native init web demo",
+    "expo": {}
}

Modify the example in App.js to not use react-native/Libraries/NewAppScreen as these components aren't universal and won't work with react-native-web.
Start the web-only project with expo start:web

Using Expo APIs

Now you can try using some universal Expo primitives. For this example we'll use a Blur view.

Install the universal package yarn add expo-blur
Implement it in your project: Blur View snack

Notice that you don't need to install any other parts of the Expo SDK to use this!

Improving Bundle Size

React Native for web requires tree-shaking for even the simplest projects, you can enable this tree-shaking by using the Expo babel preset.

Reduce the bundle size by replacing the native preset metro-react-native-babel-preset with the web-optimized babel-preset-expo
Install the web-optimized preset: yarn add -D babel-preset-expo
Modify your babel.config.js:

module.exports = {
-  presets: ['module:metro-react-native-babel-preset'],
+  presets: ['babel-preset-expo'],
};

You can now uninstall the unused dependency: yarn remove -D metro-react-native-babel-preset

This will be just enough to start the project but ideally you'll want to use node_modules/expo/AppEntry

Universal Testing

TL;DR: Run your tests on every platform with (jest-expo), not just iOS (with the react-native Jest preset).

You can read more about why universal testing is awesome here: Testing Universal React Native Apps with Jest and Expo

Install the universal testing library: yarn add -D jest-expo
Use the preset in your package.json:

"jest": {
-    "preset": "react-native"
+    "preset": "jest-expo/universal"
# OR use just a single platform
+    "preset": "jest-expo/ios"
}

Try it out with yarn test!
You can now uninstall the unused dependencies: yarn remove -D babel-jest jest react-test-renderer