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

/**
 * Copyright (c) 2015-present, Facebook, Inc.
 * All rights reserved.
 *
 * This source code is licensed under the BSD-style license found in the
 * LICENSE file in the root directory of this source tree. An additional grant
 * of patent rights can be found in the PATENTS file in the same directory.
 */
'use strict';

var path = require('path');

const plugins = [
  // class { handleClick = () => { } }
  require.resolve('babel-plugin-transform-class-properties'),
  // 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
  }],
  // Transforms JSX
  [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'))
  }]
];

// This is similar to how `env` works in Babel:
// https://babeljs.io/docs/usage/babelrc/#env-option
// We are not using `env` because it’s ignored in versions > babel-core@6.10.4:
// https://github.com/babel/babel/issues/4539
// https://github.com/facebookincubator/create-react-app/issues/720
// It’s also nice that we can enforce `NODE_ENV` being specified.
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) + '.'
  );
}

if (env === 'development' || env === 'test') {
  // The following two plugins are currently necessary to make React warnings
  // include more valuable information. They are included here because they are
  // currently not enabled in babel-preset-react. See the below threads for more info:
  // https://github.com/babel/babel/issues/4702
  // https://github.com/babel/babel/pull/3540#issuecomment-228673661
  // https://github.com/facebookincubator/create-react-app/issues/989
  plugins.push.apply(plugins, [
    // 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')
  ]);
}

if (env === 'test') {
  plugins.push.apply(plugins, [
    // We always include this plugin regardless of environment
    // because of a Babel bug that breaks object rest/spread without it:
    // https://github.com/babel/babel/issues/4851
    require.resolve('babel-plugin-transform-es2015-parameters')
  ]);

  module.exports = {
    presets: [
      // ES features necessary for user's Node version
      [require('babel-preset-env').default, {
        targets: {
          node: 'current',
        },
      }],
      // JSX, Flow
      require.resolve('babel-preset-react')
    ],
    plugins: plugins
  };
} else {
  module.exports = {
    presets: [
      // Latest stable ECMAScript features
      require.resolve('babel-preset-latest'),
      // JSX, Flow
      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
      }],
    ])
  };

  if (env === 'production') {
    // Optimization: hoist JSX that never changes out of render()
    // Disabled because of issues:
    // * https://github.com/facebookincubator/create-react-app/issues/525
    // * https://phabricator.babeljs.io/search/query/pCNlnC2xzwzx/
    // * https://github.com/babel/babel/issues/4516
    // TODO: Enable again when these issues are resolved.
    // plugins.push.apply(plugins, [
    //   require.resolve('babel-plugin-transform-react-constant-elements')
    // ]);
  }
}