"Modern" build for react-native application for iOS 12+ as target. Native async-await, classes and much more!

babel.config.js

const isLegacyBuild = typeof process.env.BUNDLE_FOR_IOS === 'undefined';
const iosVersion = process.env.BUNDLE_FOR_IOS || 12;
const modernBuild = {
  presets: [
    [
      '@babel/preset-env',
      {
        targets: `iOS >= ${iosVersion}`,
      },
    ],
    '@babel/preset-react',
    '@babel/preset-typescript',
  ],
  plugins: [
    // Flow first https://github.com/babel/babel/issues/8417#issuecomment-417858286
    '@babel/plugin-transform-flow-strip-types',
    [
      '@babel/plugin-transform-runtime',
      {
        helpers: true,
        regenerator: false,
      }
    ],
    '@babel/plugin-proposal-class-properties',
    '@babel/plugin-proposal-export-default-from',
    '@babel/plugin-proposal-optional-chaining',
    '@babel/plugin-proposal-object-rest-spread',
    '@babel/plugin-proposal-nullish-coalescing-operator',
    // 'transform-remove-strict-mode', // @TODO: add strict to whole bundle once
  ]
};

const legacyBuild = {
  presets: [
    'module:metro-react-native-babel-preset'
  ],
  plugins: [
    'transform-remove-console',
    '@babel/plugin-transform-runtime',
  ]
};

const config = {
  plugins: [
    ['module-resolver', {
      'root': ['./src'],
      'extensions': ['.js', '.ts', '.tsx', '.ios.js', '.android.js']
    }],
  ],
  env: {
    production: isLegacyBuild
      ? legacyBuild
      : {
        ...modernBuild,
        plugins: [
          ...modernBuild.plugins,
          'transform-remove-console',
        ]
      },
    development: modernBuild,
  }
};

module.exports = config;