Expo support (codesandbox#1807)

* Added support for Unimodules in the browser.

* Add @EvanBacon as a contributor

* Added Metro environment variable __DEV__

* Removed __DEV__ variable

Author: EvanBacon

.all-contributorsrc

@@ -1167,6 +1167,15 @@
       "contributions": [
         "code"
       ]
+    },
+    {
+      "login": "EvanBacon",
+      "name": "Evan Bacon",
+      "avatar_url": "https://avatars1.githubusercontent.com/u/9664363?v=4",
+      "profile": "https://twitter.com/baconbrix",
+      "contributions": [
+        "code"
+      ]
     }
   ],
   "repoType": "github",

README.md

@@ -14,7 +14,20 @@ export default function initialize() {
   const preset = new Preset(
     'create-react-app',
     ['web.js', 'js', 'json', 'web.jsx', 'jsx', 'ts', 'tsx'],
-    { 'react-native': 'react-native-web' },
+    { 
+      // Directly match react-native to react-native-web. 
+      // Attempt to use react-native internals shouldn't work on web.
+      'react-native$': 'react-native-web',
+      // Alias core react-native internals to react-native-web equivalents
+      'react-native/Libraries/EventEmitter/RCTDeviceEventEmitter$': 'react-native-web/dist/vendor/react-native/NativeEventEmitter/RCTDeviceEventEmitter',
+      'react-native/Libraries/vendor/emitter/EventEmitter$': 'react-native-web/dist/vendor/react-native/emitter/EventEmitter',
+      'react-native/Libraries/vendor/emitter/EventSubscriptionVendor$': 'react-native-web/dist/vendor/react-native/emitter/EventSubscriptionVendor',
+      'react-native/Libraries/EventEmitter/NativeEventEmitter$': 'react-native-web/dist/vendor/react-native/NativeEventEmitter',
+      // Alias core react-native asset management internals to unimodule equivalents.
+      'react-native/Libraries/Image/AssetSourceResolver$': 'expo-asset/build/AssetSourceResolver',
+      'react-native/Libraries/Image/assetPathUtils$': 'expo-asset/build/Image/assetPathUtils',
+      'react-native/Libraries/Image/resolveAssetSource$': 'expo-asset/build/resolveAssetSource',
+    },
     {
       hasDotEnv: true,
       setup: manager => {