babel.config.js

const { moduleExists } = require('shakapacker')

module.exports = function config(api) {
  var validEnv = ['development', 'test', 'production']
  var currentEnv = api.env()
  var isDevelopmentEnv = api.env('development')
  var isProductionEnv = api.env('production')
  var isTestEnv = api.env('test')

  if (!validEnv.includes(currentEnv)) {
    throw new Error(
      'Please specify a valid `NODE_ENV` or ' +
        '`BABEL_ENV` environment variables. Valid values are "development", ' +
        '"test", and "production". Instead, received: ' +
        JSON.stringify(currentEnv) +
        '.'
    )
  }

  return {
    presets: [
      isTestEnv && [
        '@babel/preset-env',
        {
          targets: {
            node: 'current'
          }
        }
      ],
      (isProductionEnv || isDevelopmentEnv) && [
        '@babel/preset-env',
        {
          useBuiltIns: 'entry',
          corejs: '3.8',
          modules: 'auto',
          bugfixes: true,
          loose: true,
          exclude: ['transform-typeof-symbol']
        }
      ]
    ].filter(Boolean),
    plugins: [
      'babel-plugin-macros',
      ['@babel/plugin-proposal-class-properties', { loose: true }],
      ['@babel/plugin-transform-runtime', { helpers: false }],
      [
        'babel-plugin-module-resolver',
        {
          root: [
            './app/frontend/assets/javascripts',
            './app/frontend/vendor/javascripts'
          ],
          alias: {}
        }
      ]
    ].filter(Boolean)
  }
}