webpack.config.babel.js

const { merge } = require('webpack-merge');
const buildValidations = require('./webpack/build-validations');
const commonConfig = require('./webpack/webpack.common');


// We can include Webpack plugins, through addons, that do
// not need to run every time we are developing.
// We will see an example when we set up 'Bundle Analyzer'
const addons = (/* string | string[] */ addonsArg) => {
  // Normalize array of addons (flatten)
  const addons = [...[addonsArg]]
    .filter(Boolean); // If addons is undefined, filter it out

  return addons.map((addonName) => require(`./webpack/addons/webpack.${addonName}.js`))
}

// 'env' will contain the environment variable from 'scripts'
// section in 'package.json'.
// console.log(env); => { env: 'dev' }

module.exports = (env) => {
  // We use 'buildValidations' to check for the 'env' flag
  if (!env) {
    throw new Error(buildValidations.ERR_NO_ENV_FLAG)
  }

  // Select which Webpack configuration to use; development
  // or production
  // console.log(env.env); => dev
  const envConfig = require(`./webpack/webpack.${env.env}.js`)

  // 'webpack-merge' will combine our shared configurations, the
  // environment specific configurations and any addons we are
  // including
  const mergedConfig = merge(commonConfig, envConfig, ...addons(env.addons))

  // Then return the final configuration for Webpack
  return mergedConfig
}