update to modern code style

package.json

@@ -8,11 +8,13 @@
     "postinstall": "lerna bootstrap",
     "publish": "tasks/release.sh",
     "start": "node packages/react-scripts/scripts/start.js",
-    "test": "node packages/react-scripts/scripts/test.js --env=jsdom"
+    "test": "node packages/react-scripts/scripts/test.js --env=jsdom",
+    "format": "prettier --trailing-comma es5 --single-quote --write 'packages/*/*.js' 'packages/*/!(node_modules)/**/*.js'"
   },
   "devDependencies": {
     "eslint": "3.16.1",
     "lerna": "2.0.0-beta.38",
-    "lerna-changelog": "^0.2.3"
+    "lerna-changelog": "^0.2.3",
+    "prettier": "^0.21.0"
   }
 }

packages/babel-preset-react-app/index.js

@@ -16,21 +16,30 @@ const plugins = [
   // The following two plugins use Object.assign directly, instead of Babel's
   // extends helper. Note that this assumes `Object.assign` is available.
   // { ...todo, completed: true }
-  [require.resolve('babel-plugin-transform-object-rest-spread'), {
-    useBuiltIns: true
-  }],
+  [
+    require.resolve('babel-plugin-transform-object-rest-spread'),
+    {
+      useBuiltIns: true,
+    },
+  ],
   // Transforms JSX
-  [require.resolve('babel-plugin-transform-react-jsx'), {
-    useBuiltIns: true
-  }],
+  [
+    require.resolve('babel-plugin-transform-react-jsx'),
+    {
+      useBuiltIns: true,
+    },
+  ],
   // Polyfills the runtime needed for async/await and generators
-  [require.resolve('babel-plugin-transform-runtime'), {
-    helpers: false,
-    polyfill: false,
-    regenerator: true,
-    // Resolve the Babel runtime relative to the config.
-    moduleName: path.dirname(require.resolve('babel-runtime/package'))
-  }]
+  [
+    require.resolve('babel-plugin-transform-runtime'),
+    {
+      helpers: false,
+      polyfill: false,
+      regenerator: true,
+      // Resolve the Babel runtime relative to the config.
+      moduleName: path.dirname(require.resolve('babel-runtime/package')),
+    },
+  ],
 ];
 
 // This is similar to how `env` works in Babel:
@@ -42,9 +51,11 @@ const plugins = [
 var env = process.env.BABEL_ENV || process.env.NODE_ENV;
 if (env !== 'development' && env !== 'test' && env !== 'production') {
   throw new Error(
-    'Using `babel-preset-react-app` requires that you specify `NODE_ENV` or '+
-    '`BABEL_ENV` environment variables. Valid values are "development", ' +
-    '"test", and "production". Instead, received: ' + JSON.stringify(env) + '.'
+    'Using `babel-preset-react-app` requires that you specify `NODE_ENV` or ' +
+      '`BABEL_ENV` environment variables. Valid values are "development", ' +
+      '"test", and "production". Instead, received: ' +
+      JSON.stringify(env) +
+      '.'
   );
 }
 
@@ -59,54 +70,63 @@ if (env === 'development' || env === 'test') {
     // Adds component stack to warning messages
     require.resolve('babel-plugin-transform-react-jsx-source'),
     // Adds __self attribute to JSX which React will use for some warnings
-    require.resolve('babel-plugin-transform-react-jsx-self')
+    require.resolve('babel-plugin-transform-react-jsx-self'),
   ]);
 }
 
 if (env === 'test') {
   module.exports = {
     presets: [
       // ES features necessary for user's Node version
-      [require('babel-preset-env').default, {
-        targets: {
-          node: 'current',
+      [
+        require('babel-preset-env').default,
+        {
+          targets: {
+            node: 'current',
+          },
         },
-      }],
+      ],
       // JSX, Flow
-      require.resolve('babel-preset-react')
+      require.resolve('babel-preset-react'),
     ],
     plugins: plugins.concat([
       // Compiles import() to a deferred require()
-      require.resolve('babel-plugin-dynamic-import-node')
-    ])
+      require.resolve('babel-plugin-dynamic-import-node'),
+    ]),
   };
 } else {
   module.exports = {
     presets: [
       // Latest stable ECMAScript features
-      [require.resolve('babel-preset-env'), {
-        targets: {
-          // React parses on ie 9, so we should too
-          ie: 9,
-          // We currently minify with uglify
-          // Remove after https://github.com/mishoo/UglifyJS2/issues/448
-          uglify: true
+      [
+        require.resolve('babel-preset-env'),
+        {
+          targets: {
+            // React parses on ie 9, so we should too
+            ie: 9,
+            // We currently minify with uglify
+            // Remove after https://github.com/mishoo/UglifyJS2/issues/448
+            uglify: true,
+          },
+          // Disable polyfill transforms
+          useBuiltIns: false,
         },
-        // Disable polyfill transforms
-        useBuiltIns: false
-      }],
+      ],
       // JSX, Flow
-      require.resolve('babel-preset-react')
+      require.resolve('babel-preset-react'),
     ],
     plugins: plugins.concat([
       // function* () { yield 42; yield 43; }
-      [require.resolve('babel-plugin-transform-regenerator'), {
-        // Async functions are converted to generators by babel-preset-latest
-        async: false
-      }],
+      [
+        require.resolve('babel-plugin-transform-regenerator'),
+        {
+          // Async functions are converted to generators by babel-preset-latest
+          async: false,
+        },
+      ],
       // Adds syntax support for import()
       require.resolve('babel-plugin-syntax-dynamic-import'),
-    ])
+    ]),
   };
 
   if (env === 'production') {