registerServiceWorker.js

async _registerServiceWorker() {
  // Instructions on how to toast the user when necessary. 🍾
  const toast = () => this.$.swtoast.open();
  // Listen for changes on a new worker, toast when installed. 🍞
  const track = (sw) => sw.onstatechange = () => (sw.state === 'installed') && toast();
  // Register the service worker
  const scope = Polymer.rootPath;
  let reg;
  try {
    reg = await navigator.serviceWorker.register('/service-worker.js', {scope});
  } catch (e) {
    // eslint-disable-next-line no-console
    return console.info('Could not register service worker.', e);
  }
  // If there's no previous SW, quit early - this page load is fresh. 🍌
  if (!navigator.serviceWorker.controller) return;
  // A new SW is already waiting to activate. Toast the user to update. 👯
  // Or, if user has not yet interacted with the page, reload.
  else if (reg.waiting) return this._hasInteracted
    ? toast()
    : location.reload();
  // A new SW is installing. Listen for updates, toast when installed. 🍻
  else if (reg.installing) track(reg.installing);
  // Otherwise, when a new service worker arrives, listen for updates,
  // and if it becomes installed, toast the user. 🍷
  else reg.onupdatefound = () => track(reg.installing);
}