Drop IE 11 support by default (#5090)

* Drop ie 11 support and move polyfills to a new package

* More useful directions for what entry point to use
#5090 (comment)

* Clear up what file this polyfill goes in
#5090 (comment)

* Polyfill `window`, not `global`

* Remove proxy polyfill file

Author: Timer

Diff for: packages/react-app-polyfill/README.md

@@ -0,0 +1,40 @@
+# react-app-polyfill
+
+This package includes polyfills for various browsers.
+It includes minimum requirements and commonly used language features used by [Create React App](https://github.com/facebook/create-react-app) projects.<br>
+Please refer to its documentation:
+
+- [Getting Started](https://github.com/facebook/create-react-app/blob/master/README.md#getting-started) – How to create a new app.
+- [User Guide](https://github.com/facebook/create-react-app/blob/master/packages/react-scripts/template/README.md) – How to develop apps bootstrapped with Create React App.
+
+### Features
+
+Each polyfill ensures the following language features are present:
+
+1. `Promise` (for `async` / `await` support)
+1. `window.fetch` (a Promise-based way to make web requests in the browser)
+1. `Object.assign` (a helper required for Object Spread, i.e. `{ ...a, ...b }`)
+1. `Symbol` (a built-in object used by `for...of` syntax and friends)
+1. `Array.from` (a built-in static method used by array spread, i.e. `[...arr]`)
+
+### Entry Points
+
+You can import the entry point for the minimal version you intend to support. For example, if you import the IE9 entry point, this will include IE10 and IE11 support.
+
+#### Internet Explorer 9
+
+```js
+// This must be the first line in src/index.js
+import 'react-app-polyfill/ie9';
+
+// ...
+```
+
+#### Internet Explorer 11
+
+```js
+// This must be the first line in src/index.js
+import 'react-app-polyfill/ie11';
+
+// ...
+```

Diff for: packages/react-scripts/config/polyfills.js renamed to packages/react-app-polyfill/ie11.js

@@ -1,11 +1,9 @@
-// @remove-on-eject-begin
 /**
  * Copyright (c) 2015-present, Facebook, Inc.
  *
  * This source code is licensed under the MIT license found in the
  * LICENSE file in the root directory of this source tree.
  */
-// @remove-on-eject-end
 'use strict';
 
 if (typeof Promise === 'undefined') {
@@ -23,8 +21,7 @@ require('whatwg-fetch');
 // It will use the native implementation if it's present and isn't buggy.
 Object.assign = require('object-assign');
 
-// In tests, polyfill requestAnimationFrame since jsdom doesn't provide it yet.
-// We don't polyfill it in the browser--this is user's responsibility.
-if (process.env.NODE_ENV === 'test') {
-  require('raf').polyfill(global);
-}
+// Support for...of (a commonly used syntax feature that requires Symbols)
+require('core-js/es6/symbol');
+// Support iterable spread (...Set, ...Map)
+require('core-js/fn/array/from');

Diff for: packages/react-app-polyfill/ie9.js

@@ -0,0 +1,32 @@
+/**
+ * Copyright (c) 2015-present, Facebook, Inc.
+ *
+ * This source code is licensed under the MIT license found in the
+ * LICENSE file in the root directory of this source tree.
+ */
+'use strict';
+
+if (typeof Promise === 'undefined') {
+  // Rejection tracking prevents a common issue where React gets into an
+  // inconsistent state due to an error, but it gets swallowed by a Promise,
+  // and the user has no idea what causes React's erratic future behavior.
+  require('promise/lib/rejection-tracking').enable();
+  window.Promise = require('promise/lib/es6-extensions.js');
+}
+
+// fetch() polyfill for making API calls.
+require('whatwg-fetch');
+
+// Object.assign() is commonly used with React.
+// It will use the native implementation if it's present and isn't buggy.
+Object.assign = require('object-assign');
+
+// Support for...of (a commonly used syntax feature that requires Symbols)
+require('core-js/es6/symbol');
+// Support iterable spread (...Set, ...Map)
+require('core-js/fn/array/from');
+
+// React 16+ relies on Map, Set, and requestAnimationFrame
+require('core-js/es6/map');
+require('core-js/es6/set');
+require('raf').polyfill(window);

Diff for: packages/react-app-polyfill/jsdom.js

@@ -0,0 +1,10 @@
+/**
+ * Copyright (c) 2015-present, Facebook, Inc.
+ *
+ * This source code is licensed under the MIT license found in the
+ * LICENSE file in the root directory of this source tree.
+ */
+'use strict';
+
+// fetch() polyfill for making API calls.
+require('whatwg-fetch');

Diff for: packages/react-app-polyfill/package.json

@@ -0,0 +1,25 @@
+{
+  "name": "react-app-polyfill",
+  "version": "0.0.0",
+  "description": "Polyfills for various browsers including commonly used language features",
+  "repository": "facebook/create-react-app",
+  "license": "MIT",
+  "bugs": {
+    "url": "https://github.com/facebook/create-react-app/issues"
+  },
+  "engines": {
+    "node": ">=6"
+  },
+  "files": [
+    "ie9.js",
+    "ie11.js",
+    "jsdom.js"
+  ],
+  "dependencies": {
+    "core-js": "2.5.7",
+    "object-assign": "4.1.1",
+    "promise": "8.0.2",
+    "raf": "3.4.0",
+    "whatwg-fetch": "3.0.0"
+  }
+}

Diff for: packages/react-scripts/config/webpack.config.dev.js

@@ -82,10 +82,7 @@ module.exports = {
   devtool: 'cheap-module-source-map',
   // These are the "entry points" to our application.
   // This means they will be the "root" imports that are included in JS bundle.
-  // The first two entry points enable "hot" CSS and auto-refreshes for JS.
   entry: [
-    // We ship a few polyfills by default:
-    require.resolve('./polyfills'),
     // Include an alternative client for WebpackDevServer. A client's job is to
     // connect to WebpackDevServer by a socket and get notified about changes.
     // When you save a file, the client will either apply hot updates (in case

Diff for: packages/react-scripts/config/webpack.config.prod.js

@@ -100,8 +100,8 @@ module.exports = {
   // We generate sourcemaps in production. This is slow but gives good results.
   // You can exclude the *.map files from the build during deployment.
   devtool: shouldUseSourceMap ? 'source-map' : false,
-  // In production, we only want to load the polyfills and the app code.
-  entry: [require.resolve('./polyfills'), paths.appIndexJs],
+  // In production, we only want to load the app code.
+  entry: [paths.appIndexJs],
   output: {
     // The build folder.
     path: paths.appBuild,

Diff for: packages/react-scripts/package.json

@@ -50,14 +50,12 @@
     "jest": "23.6.0",
     "loader-utils": "1.1.0",
     "mini-css-extract-plugin": "0.4.3",
-    "object-assign": "4.1.1",
     "optimize-css-assets-webpack-plugin": "5.0.1",
     "postcss-flexbugs-fixes": "4.1.0",
     "postcss-loader": "3.0.0",
     "postcss-preset-env": "6.0.6",
     "postcss-safe-parser": "4.0.1",
-    "promise": "8.0.2",
-    "raf": "3.4.0",
+    "react-app-polyfill": "^0.0.0",
     "react-dev-utils": "^5.0.0",
     "resolve": "1.8.1",
     "sass-loader": "7.1.0",
@@ -68,8 +66,7 @@
     "url-loader": "1.1.1",
     "webpack": "4.19.1",
     "webpack-dev-server": "3.1.9",
-    "webpack-manifest-plugin": "2.0.4",
-    "whatwg-fetch": "3.0.0"
+    "webpack-manifest-plugin": "2.0.4"
   },
   "devDependencies": {
     "react": "^16.3.2",

Diff for: packages/react-scripts/scripts/utils/createJestConfig.js

@@ -22,7 +22,7 @@ module.exports = (resolve, rootDir, isEjecting) => {
   // in Jest configs. We need help from somebody with Windows to determine this.
   const config = {
     collectCoverageFrom: ['src/**/*.{js,jsx}'],
-    setupFiles: [resolve('config/polyfills.js')],
+    setupFiles: ['react-app-polyfill/jsdom'],
     setupTestFrameworkScriptFile: setupTestsFile,
     testMatch: [
       '<rootDir>/src/**/__tests__/**/*.{js,jsx}',