index.js

const path = require('path')

module.exports = function (api, opts = {}) {
  api.cache(true)

  const env = process.env.BABEL_ENV || process.env.NODE_ENV

  const isEnvDevelopment = env === 'development'
  const isEnvProduction = env === 'production'
  const isEnvTest = env === 'test'

  if (!isEnvDevelopment && !isEnvProduction && !isEnvTest) {
    throw new Error(
      'Using `@by-association-only/babel-preset-unisian` requires that you specify `NODE_ENV` or ' +
      '`BABEL_ENV` environment variables. Valid values are "development", ' +
      '"test", and "production". Instead, received: ' +
      JSON.stringify(env) +
      '.'
    )
  }

  const areHelpersEnabled = false
  const useAbsoluteRuntime = true

  let absoluteRuntimePath = undefined

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

  return {
    presets: [
      isEnvTest && [
        // ES features necessary for user's Node version
        require('@babel/preset-env').default,
        {
          targets: {
            node: 'current'
          }
        }
      ],
      (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,
          // Do not transform modules to CJS
          modules: false,
          // Exclude transforms that make all code slower
          exclude: ['transform-typeof-symbol']
        }
      ],
    ].filter(Boolean),
    plugins: [
      [
        require('@babel/plugin-proposal-class-properties').default,
        {
          loose: true
        }
      ],
      [
        require('@babel/plugin-proposal-private-methods').default,
        {
          loose: true
        }
      ],
      require('@babel/plugin-proposal-numeric-separator').default,
      [
        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: false,
          // 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
        }
      ],
      // Optional chaining and nullish coalescing are supported in @babel/preset-env,
      // but not yet supported in webpack due to support missing from acorn.
      // These can be removed once webpack has support.
      require('@babel/plugin-proposal-optional-chaining').default,
      require('@babel/plugin-proposal-nullish-coalescing-operator').default
    ].filter(Boolean)
  }
}