Created preact example

with-preact/App.js

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+import React from 'react';
+import { StyleSheet, Text, View } from 'react-native';
+
+export default function App() {
+  return (
+    <View style={styles.container}>
+      <Text>Demo Preact + Expo web</Text>
+    </View>
+  );
+}
+
+const styles = StyleSheet.create({
+  container: {
+    flex: 1,
+    backgroundColor: '#fff',
+    alignItems: 'center',
+    justifyContent: 'center',
+  },
+});

with-preact/README.md

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+# Preact Example
+
+> 💡 The most updated info is in the Expo docs: [Using Preact](https://github.com/expo/expo/blob/master/docs/pages/versions/unversioned/guides/using-preact.md)
+
+[Preact](https://preactjs.com/) is "a fast 3kB alternative to React" with the same modern API as React. Preact was created by [Jason Miller](https://twitter.com/_developit).
+
+## Before Preact
+
+If you create a standard Expo web project (at the time of writing this), the bundle size will look something like the report below. 
+
+**❌ 60.75 KB Gzipped**
+
+![expo web bundle without preact](.gh-assets/before-preact.png "Expo web bundle without Preact")
+
+> 💡 You can [**enable** bundle reporting easily!](https://github.com/expo/expo/blob/master/docs/pages/versions/unversioned/guides/web-performance.md#-what-makes-my-app-large)
+
+## After Preact
+
+After modifying your project to use Preact instead of React DOM, the bundle will reduce drastically meaning your website will load faster and work much better for poor internet connections.
+
+**✅ 27.98 KB Gzipped**
+
+![expo web bundle with preact](.gh-assets/after-preact.png "Expo web bundle with Preact")
+
+### ⚽️ Getting Started
+
+To use Preact with React Native for web, you'll need to install the packages and alias them to React. You may also want to enable **reporting** so you can analyze your bundle size.
+
+- Install Preact (requires Preact 10+): `yarn add preact-responder-event-plugin preact`
+- Run `expo customize:web` and select `webpack.config.js`
+- Modify the webpack config to use Preact instead of React:
+
+  ```js
+  const createExpoWebpackConfigAsync = require('@expo/webpack-config');
+
+  module.exports = async function(env, argv) {
+    const config = await createExpoWebpackConfigAsync({
+        ...env,
+        // Optionally you can enable the bundle size report
+        report: true
+    }, argv);
+
+    // Add more aliases
+    config.resolve.alias = {
+      ...config.resolve.alias,
+      // Use Preact aliases
+      react$: 'preact/compat',
+      'react-dom$': 'preact/compat',
+      // Fix the responder system which react-native-web depends on
+      'react-dom/unstable-native-dependencies$': 'preact-responder-event-plugin',
+    };
+    return config;
+  };
+  ```
+
+- That's it! Running `expo build:web` will now produce a significantly smaller bundle.

with-preact/app.json

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+{
+  "expo": {
+    "name": "with-preact",
+    "version": "1.0.0",
+    "icon": "https://github.com/expo/expo/blob/master/templates/expo-template-blank/assets/icon.png?raw=true",
+    "splash": {
+      "image": "https://github.com/expo/expo/blob/master/templates/expo-template-blank/assets/splash.png?raw=true",
+      "resizeMode": "contain",
+      "backgroundColor": "#ffffff"
+    }
+  }
+}

with-preact/babel.config.js

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+module.exports = function(api) {
+  api.cache(true);
+  return {
+    presets: ['babel-preset-expo'],
+  };
+};

with-preact/package.json

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+{
+  "dependencies": {
+    "expo": "36.0.0",
+    "preact": "10.2.1",
+    "preact-responder-event-plugin": "1.0.14",
+    "react": "16.9.0",
+    "react-dom": "16.9.0",
+    "react-native": "https://github.com/expo/react-native/archive/sdk-36.0.0.tar.gz",
+    "react-native-web": "0.11.7"
+  },
+  "devDependencies": {
+    "@babel/core": "7.0.0",
+    "@expo/webpack-config": "0.10.11",
+    "babel-preset-expo": "8.0.0"
+  }
+}

with-preact/webpack.config.js

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+const createExpoWebpackConfigAsync = require('@expo/webpack-config');
+
+module.exports = async function(env, argv) {
+  const config = await createExpoWebpackConfigAsync({ ...env, report: true }, argv);
+
+  config.resolve.alias = {
+    ...config.resolve.alias,
+    // Use Preact aliases
+    react$: 'preact/compat',
+    'react-dom$': 'preact/compat',
+    // Fix the responder system which react-native-web depends on
+    'react-dom/unstable-native-dependencies$': 'preact-responder-event-plugin',
+  };
+  return config;
+};