Example loading in "workbox.js"

workbox.js

class Workbox {
  loadModule(moduleName) {
    // Load workbox module from CDN
    importScripts(`https://some-cdn.cdn.com/${moduleName}/build/umd.js`);
  }

  get precaching() {
    if (google.workbox.precaching) {
      return google.workbox.precaching.default;
    }

    this.loadModule('workbox-precaching');
    return google.workbox.precaching.default;
  }
}