Small tweak to Sean Larkins' LoadPresets script for Webpack

loadPresets.js

// Original: https://github.com/TheLarkInn/webpack-workshop-2018/blob/feature/build-utils/build-utils/loadPresets.js
/**
 * Usage:
 * Use via NPM script
 * Passing a single preset:
 * "prod:compress": "npm run prod -- --env.presets compress",
 * "prod:analyze": "npm run prod -- --env.presets analyze",
 * Passing a multiple preset as a , separate list:
 * "prod:compress-analyze": "npm run prod -- --env.presets compress,analyze",
 */
const webpackMerge = require("webpack-merge");

const applyPresets = (env = { presets: [] }) => {
  let presets = env.presets || [];
  // only split if the array has more than one item
  if (presets.length) {
    presets = presets.split(",");
  }
  /** @type {string[]} */
  const mergedPresets = [].concat(...[presets]);
  const mergedConfigs = mergedPresets.map(presetName =>
    require(`./presets/webpack.${presetName}`)(env)
  );

  return webpackMerge({}, ...mergedConfigs);
};

module.exports = applyPresets;