dependencies.js

/**
 * 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';

const path = require('path');

const validateBoolOption = (name, value, defaultValue) => {
  if (typeof value === 'undefined') {
    value = defaultValue;
  }

  if (typeof value !== 'boolean') {
    throw new Error(`Preset react-app: '${name}' option must be a boolean.`);
  }

  return value;
};

module.exports = function (api, opts) {
  if (!opts) {
    opts = {};
  }

  // 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/facebook/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;
  var isEnvDevelopment = env === 'development';
  var isEnvProduction = env === 'production';
  var isEnvTest = env === 'test';

  var areHelpersEnabled = validateBoolOption('helpers', opts.helpers, false);
  var useAbsoluteRuntime = validateBoolOption(
    'absoluteRuntime',
    opts.absoluteRuntime,
    true
  );

  var absoluteRuntimePath = undefined;
  if (useAbsoluteRuntime) {
    absoluteRuntimePath = path.dirname(
      require.resolve('@babel/runtime/package.json')
    );
  }

  if (!isEnvDevelopment && !isEnvProduction && !isEnvTest) {
    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) +
        '.'
    );
  }

  return {
    // Babel assumes ES Modules, which isn't safe until CommonJS
    // dies. This changes the behavior to assume CommonJS unless
    // an `import` or `export` is present in the file.
    // https://github.com/webpack/webpack/issues/4039#issuecomment-419284940
    sourceType: 'unambiguous',
    presets: [
      isEnvTest && [
        // ES features necessary for user's Node version
        require('@babel/preset-env').default,
        {
          targets: {
            node: 'current',
          },
          // Exclude transforms that make all code slower
          exclude: ['transform-typeof-symbol'],
        },
      ],
      (isEnvProduction || isEnvDevelopment) && [
        // Latest stable ECMAScript features
        require('@babel/preset-env').default,
        {
          // Allow importing core-js in entrypoint and use browserlist to select polyfills
          useBuiltIns: 'entry',
          // Set the corejs version we are using to avoid warnings in console
          // This will need to change once we upgrade to corejs@3
          corejs: 3,
          // Exclude transforms that make all code slower
          exclude: ['transform-typeof-symbol'],
        },
      ],
    ].filter(Boolean),
    plugins: [
      // Disabled as it's handled automatically by preset-env, and `selectiveLoose` isn't
      // yet merged into babel: https://github.com/babel/babel/pull/9486
      // Related: https://github.com/facebook/create-react-app/pull/8215
      // [
      //   require('@babel/plugin-transform-destructuring').default,
      //   {
      //     // Use loose mode for performance:
      //     // https://github.com/facebook/create-react-app/issues/5602
      //     loose: false,
      //     selectiveLoose: [
      //       'useState',
      //       'useEffect',
      //       'useContext',
      //       'useReducer',
      //       'useCallback',
      //       'useMemo',
      //       'useRef',
      //       'useImperativeHandle',
      //       'useLayoutEffect',
      //       'useDebugValue',
      //     ],
      //   },
      // ],
      // Polyfills the runtime needed for async/await, generators, and friends
      // https://babeljs.io/docs/en/babel-plugin-transform-runtime
      [
        require('@babel/plugin-transform-runtime').default,
        {
          corejs: false,
          helpers: areHelpersEnabled,
          // By default, babel assumes babel/runtime version 7.0.0-beta.0,
          // explicitly resolving to match the provided helper functions.
          // https://github.com/babel/babel/issues/10261
          version: require('@babel/runtime/package.json').version,
          regenerator: true,
          // https://babeljs.io/docs/en/babel-plugin-transform-runtime#useesmodules
          // We should turn this on once the lowest version of Node LTS
          // supports ES Modules.
          useESModules: isEnvDevelopment || isEnvProduction,
          // Undocumented option that lets us encapsulate our runtime, ensuring
          // the correct version is used
          // https://github.com/babel/babel/blob/090c364a90fe73d36a30707fc612ce037bdbbb24/packages/babel-plugin-transform-runtime/src/index.js#L35-L42
          absoluteRuntime: absoluteRuntimePath,
        },
      ],
    ].filter(Boolean),
  };
};