babel.config.js

// This file is seen only by Babel 7, not Babel 6.
// There are other semantic differences: see
//   https://babeljs.io/docs/en/config-files

module.exports = {
  presets: [
    'module:metro-react-native-babel-preset',
  ],
  plugins: [
    // We can remove this once it's included in
    // metro-react-native-babel-preset; see
    // https://github.com/facebook/metro/issues/645. It's already in
    // @babel/reset-env, but that doesn't get used as a base plugin; see a
    // comment on that issue explaining why.
    '@babel/plugin-proposal-numeric-separator',

    // Flow enums:
    //   https://flow.org/en/docs/enums/enabling-enums/#toc-enable-enums
    [
      '@babel/plugin-syntax-flow',
      // Required by 'transform-flow-enums':
      //   https://www.npmjs.com/package/babel-plugin-transform-flow-enums
      { enums: true }
    ],
    'transform-flow-enums'
  ],
};