New config

config/babel.dev.js

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+module.exports = {
+  // Don't try to find .babelrc because we want to force this configuration.
+  babelrc: false,
+  // This is a feature of `babel-loader` for webpack (not Babel itself).
+  // It enables caching results in OS temporary directory for faster rebuilds.
+  cacheDirectory: true,
+  presets: [
+    // Latest stable ECMAScript features
+    require.resolve('babel-preset-latest'),
+    // JSX, Flow
+    require.resolve('babel-preset-react')
+  ],
+  plugins: [
+    // class { handleClick = () => { } }
+    require.resolve('babel-plugin-transform-class-properties'),
+    // { ...todo, completed: true }
+    require.resolve('babel-plugin-transform-object-rest-spread'),
+    // function* () { yield 42; yield 43; }
+    [require.resolve('babel-plugin-transform-regenerator'), {
+      // Async functions are converted to generators by babel-preset-latest
+      async: false
+    }],
+    // Polyfills the runtime needed for async/await and generators
+    [require.resolve('babel-plugin-transform-runtime'), {
+      helpers: false,
+      polyfill: false,
+      regenerator: true
+    }]
+  ]
+};

config/babel.prod.js

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+module.exports = {
+  // Don't try to find .babelrc because we want to force this configuration.
+  babelrc: false,
+  presets: [
+    // Latest stable ECMAScript features
+    require.resolve('babel-preset-latest'),
+    // JSX, Flow
+    require.resolve('babel-preset-react')
+  ],
+  plugins: [
+    // class { handleClick = () => { } }
+    require.resolve('babel-plugin-transform-class-properties'),
+    // { ...todo, completed: true }
+    require.resolve('babel-plugin-transform-object-rest-spread'),
+    // function* () { yield 42; yield 43; }
+    [require.resolve('babel-plugin-transform-regenerator'), {
+      // Async functions are converted to generators by babel-preset-latest
+      async: false
+    }],
+    // Polyfills the runtime needed for async/await and generators
+    [require.resolve('babel-plugin-transform-runtime'), {
+      helpers: false,
+      polyfill: false,
+      regenerator: true
+    }],
+    // Optimization: hoist JSX that never changes out of render()
+    require.resolve('babel-plugin-transform-react-constant-elements')
+  ],
+};

config/env.js

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+// Grab NODE_ENV and REACT_APP_* environment variables and prepare them to be
+ // injected into the application via DefinePlugin in Webpack configuration.
+
+var REACT_APP = /^REACT_APP_/i;
+var NODE_ENV = JSON.stringify(process.env.NODE_ENV || 'development');
+
+module.exports = Object
+  .keys(process.env)
+  .filter(key => REACT_APP.test(key))
+  .reduce((env, key) => {
+    env['process.env.' + key] = JSON.stringify(process.env[key]);
+    return env;
+  }, {
+    'process.env.NODE_ENV': NODE_ENV
+  });

config/eslint.js

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+// Inspired by https://github.com/airbnb/javascript but less opinionated.
+
+// We use eslint-loader so even warnings are very visibile.
+// This is why we only use "WARNING" level for potential errors,
+// and we don't use "ERROR" level at all.
+
+// In the future, we might create a separate list of rules for production.
+// It would probably be more strict.
+
+module.exports = {
+  root: true,
+
+  parser: 'babel-eslint',
+
+  // import plugin is termporarily disabled, scroll below to see why
+  plugins: [/*'import', */'flowtype', 'jsx-a11y', 'react'],
+
+  env: {
+    browser: true,
+    commonjs: true,
+    es6: true,
+    node: true
+  },
+
+  parserOptions: {
+    ecmaVersion: 6,
+    sourceType: 'module',
+    ecmaFeatures: {
+      jsx: true,
+      generators: true,
+      experimentalObjectRestSpread: true
+    }
+  },
+
+  settings: {
+    'import/ignore': [
+      'node_modules',
+      '\\.(json|css|jpg|png|gif|eot|otf|webp|svg|ttf|woff|woff2|mp4|webm)$',
+    ],
+    'import/extensions': ['.js'],
+    'import/resolver': {
+      node: {
+        extensions: ['.js', '.json']
+      }
+    }
+  },
+
+  rules: {
+    // http://eslint.org/docs/rules/
+    'array-callback-return': 'warn',
+    'default-case': ['warn', { commentPattern: '^no default$' }],
+    'dot-location': ['warn', 'property'],
+    eqeqeq: ['warn', 'allow-null'],
+    'guard-for-in': 'warn',
+    'new-parens': 'warn',
+    'no-array-constructor': 'warn',
+    'no-caller': 'warn',
+    'no-cond-assign': ['warn', 'always'],
+    'no-const-assign': 'warn',
+    'no-control-regex': 'warn',
+    'no-delete-var': 'warn',
+    'no-dupe-args': 'warn',
+    'no-dupe-class-members': 'warn',
+    'no-dupe-keys': 'warn',
+    'no-duplicate-case': 'warn',
+    'no-empty-character-class': 'warn',
+    'no-empty-pattern': 'warn',
+    'no-eval': 'warn',
+    'no-ex-assign': 'warn',
+    'no-extend-native': 'warn',
+    'no-extra-bind': 'warn',
+    'no-extra-label': 'warn',
+    'no-fallthrough': 'warn',
+    'no-func-assign': 'warn',
+    'no-implied-eval': 'warn',
+    'no-invalid-regexp': 'warn',
+    'no-iterator': 'warn',
+    'no-label-var': 'warn',
+    'no-labels': ['warn', { allowLoop: false, allowSwitch: false }],
+    'no-lone-blocks': 'warn',
+    'no-loop-func': 'warn',
+    'no-mixed-operators': ['warn', {
+      groups: [
+        ['&', '|', '^', '~', '<<', '>>', '>>>'],
+        ['==', '!=', '===', '!==', '>', '>=', '<', '<='],
+        ['&&', '||'],
+        ['in', 'instanceof']
+      ],
+      allowSamePrecedence: false
+    }],
+    'no-multi-str': 'warn',
+    'no-native-reassign': 'warn',
+    'no-negated-in-lhs': 'warn',
+    'no-new-func': 'warn',
+    'no-new-object': 'warn',
+    'no-new-symbol': 'warn',
+    'no-new-wrappers': 'warn',
+    'no-obj-calls': 'warn',
+    'no-octal': 'warn',
+    'no-octal-escape': 'warn',
+    'no-redeclare': 'warn',
+    'no-regex-spaces': 'warn',
+    'no-restricted-syntax': [
+      'warn',
+      'LabeledStatement',
+      'WithStatement',
+    ],
+    'no-return-assign': 'warn',
+    'no-script-url': 'warn',
+    'no-self-assign': 'warn',
+    'no-self-compare': 'warn',
+    'no-sequences': 'warn',
+    'no-shadow-restricted-names': 'warn',
+    'no-sparse-arrays': 'warn',
+    'no-this-before-super': 'warn',
+    'no-throw-literal': 'warn',
+    'no-undef': 'warn',
+    'no-unexpected-multiline': 'warn',
+    'no-unreachable': 'warn',
+    'no-unused-expressions': 'warn',
+    'no-unused-labels': 'warn',
+    'no-unused-vars': ['warn', { vars: 'local', args: 'none' }],
+    'no-use-before-define': ['warn', 'nofunc'],
+    'no-useless-computed-key': 'warn',
+    'no-useless-concat': 'warn',
+    'no-useless-constructor': 'warn',
+    'no-useless-escape': 'warn',
+    'no-useless-rename': ['warn', {
+      ignoreDestructuring: false,
+      ignoreImport: false,
+      ignoreExport: false,
+    }],
+    'no-with': 'warn',
+    'no-whitespace-before-property': 'warn',
+    'operator-assignment': ['warn', 'always'],
+    radix: 'warn',
+    'require-yield': 'warn',
+    'rest-spread-spacing': ['warn', 'never'],
+    strict: ['warn', 'never'],
+    'unicode-bom': ['warn', 'never'],
+    'use-isnan': 'warn',
+    'valid-typeof': 'warn',
+
+    // https://github.com/benmosher/eslint-plugin-import/blob/master/docs/rules/
+
+    // TODO: import rules are temporarily disabled because they don't play well
+    // with how eslint-loader only checks the file you change. So if module A
+    // imports module B, and B is missing a default export, the linter will
+    // record this as an issue in module A. Now if you fix module B, the linter
+    // will not be aware that it needs to re-lint A as well, so the error
+    // will stay until the next restart, which is really confusing.
+
+    // This is probably fixable with a patch to eslint-loader.
+    // When file A is saved, we want to invalidate all files that import it
+    // *and* that currently have lint errors. This should fix the problem.
+
+    // 'import/default': 'warn',
+    // 'import/export': 'warn',
+    // 'import/named': 'warn',
+    // 'import/namespace': 'warn',
+    // 'import/no-amd': 'warn',
+    // 'import/no-duplicates': 'warn',
+    // 'import/no-extraneous-dependencies': 'warn',
+    // 'import/no-named-as-default': 'warn',
+    // 'import/no-named-as-default-member': 'warn',
+    // 'import/no-unresolved': ['warn', { commonjs: true }],
+
+    // https://github.com/yannickcr/eslint-plugin-react/tree/master/docs/rules
+    'react/jsx-equals-spacing': ['warn', 'never'],
+    'react/jsx-no-duplicate-props': ['warn', { ignoreCase: true }],
+    'react/jsx-no-undef': 'warn',
+    'react/jsx-pascal-case': ['warn', {
+      allowAllCaps: true,
+      ignore: [],
+    }],
+    'react/jsx-uses-react': 'warn',
+    'react/jsx-uses-vars': 'warn',
+    'react/no-deprecated': 'warn',
+    'react/no-direct-mutation-state': 'warn',
+    'react/no-is-mounted': 'warn',
+    'react/react-in-jsx-scope': 'warn',
+    'react/require-render-return': 'warn',
+
+    // https://github.com/evcohen/eslint-plugin-jsx-a11y/tree/master/docs/rules
+    'jsx-a11y/aria-role': 'warn',
+    'jsx-a11y/img-has-alt': 'warn',
+    'jsx-a11y/img-redundant-alt': 'warn',
+    'jsx-a11y/no-access-key': 'warn',
+
+    // https://github.com/gajus/eslint-plugin-flowtype
+    'flowtype/define-flow-type': 'warn',
+    'flowtype/require-valid-file-annotation': 'warn',
+    'flowtype/use-flow-type': 'warn'
+  }
+};

config/flow/css.js.flow

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+// @flow

config/flow/file.js.flow

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+// @flow
+declare export default string;

config/paths.js

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+// TODO: we can split this file into several files (pre-eject, post-eject, test)
+// and use those instead. This way we don't need to branch here.
+
+var path = require('path');
+
+// True after ejecting, false when used as a dependency
+var isEjected = (
+  path.resolve(path.join(__dirname, '..')) ===
+  path.resolve(process.cwd())
+);
+
+// Are we developing create-react-app locally?
+var isInCreateReactAppSource = (
+  process.argv.some(arg => arg.indexOf('--debug-template') > -1)
+);
+
+function resolveOwn(relativePath) {
+  return path.resolve(__dirname, relativePath);
+}
+
+function resolveApp(relativePath) {
+  return path.resolve(relativePath);
+}
+
+if (isInCreateReactAppSource) {
+  // create-react-app development: we're in ./config/
+  module.exports = {
+    appBuild: resolveOwn('../build'),
+    appHtml: resolveOwn('../template/index.html'),
+    appFavicon: resolveOwn('../template/favicon.ico'),
+    appPackageJson: resolveOwn('../package.json'),
+    appSrc: resolveOwn('../template/src'),
+    appNodeModules: resolveOwn('../node_modules'),
+    ownNodeModules: resolveOwn('../node_modules')
+  };
+} else if (!isEjected) {
+  // before eject: we're in ./node_modules/react-scripts/config/
+  module.exports = {
+    appBuild: resolveApp('build'),
+    appHtml: resolveApp('index.html'),
+    appFavicon: resolveApp('favicon.ico'),
+    appPackageJson: resolveApp('package.json'),
+    appSrc: resolveApp('src'),
+    appLib: resolveApp('lib'),
+    appDist: resolveApp('dist'),
+    appNodeModules: resolveApp('node_modules'),
+    // this is empty with npm3 but node resolution searches higher anyway:
+    ownNodeModules: resolveOwn('../node_modules')
+  };
+} else {
+  // after eject: we're in ./config/
+  module.exports = {
+    appBuild: resolveApp('build'),
+    appHtml: resolveApp('index.html'),
+    appFavicon: resolveApp('favicon.ico'),
+    appPackageJson: resolveApp('package.json'),
+    appSrc: resolveApp('src'),
+    appLib: resolveApp('lib'),
+    appDist: resolveApp('dist'),
+    appNodeModules: resolveApp('node_modules'),
+    ownNodeModules: resolveApp('node_modules')
+  };
+}

config/polyfills.js

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+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');