All the config you need to get expo build:web to output code that's compatible with iOS 9 and Internet Explorer 11, in one easy to use package.

1. Install package

   npm install --save-dev expo-legacy-browser-support

2. Configure babel (babel.config.js)

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

3. Add WebPack config (webpack.config.js)

   module.exports = require('expo-legacy-browser-support/webpack')

4. Add polyfills (package.json)

    {
      "version": "0.0.0",
   -  "main": "node_modules/expo/AppEntry.js",
   +  "main": "node_modules/expo-legacy-browser-support/AppEntry.js",
      "private": true,
      "scripts": {