sw-register.js

navigator.serviceWorker
  .register("/sw.js")
  .then((reg) => {
    // no controller exist, page wasn't loaded via a service worker
    if (!navigator.serviceWorker.controller) {
      return;
    }

    if (reg.waiting) {
      // If we have a new version of the service worker is waiting,
      // we can display the message to the user and allow them
      // to trigger updates manually.
      // Otherwise, the browser will replace the service worker
      // when the user closes or navigate away from all tabs using
      // the current service worker.
      return;
    }
    if (reg.installing) {
      // If we have a new service worker is installing, we can
      // tracking the status and display the message once the
      // installation is finished.
      return;
    }
  });