[REQUIRED] Describe your environment

• Operating System version: Windows 10 Home 19043.1526
• Browser version: 98.0.4758.82 (Official Build) (64-bit)
• Firebase SDK version: ^9.0.0-beta.1
• Firebase Product: messaging

[REQUIRED] Describe the problem
Calling messaging getToken sometimes throws the error: Failed to execute 'subscribe' on 'PushManager': Subscription failed - no active Service Worker

This occurs when a user has not yet registered the service worker i.e. it is their first visit to the web app or their first usage of a feature that involves the use of the service worker -> since getToken does not register the SW until that point.

It seems there may be a race condition where the service worker may or may not be ready when
const subscription = await swRegistration.pushManager.getSubscription(); is called here

Other online sources here https://stackoverflow.com/questions/42063006/failed-to-subscribe-the-user-domexception-subscription-failed-no-active-serv and here bradtraversy/node_push_notifications#1 (comment) seem to solve this issue with the line await navigator.serviceWorker.ready; to wait for the service worker to be ready,

This may be connected to issue 5797 here #5797.

Steps to reproduce:

Caveat: in most cases the steps below will not trigger the issue, it will only occur when the service worker is not ready

1. Clear cache & remove notification permission
2. Add firebase-messaging-sw.js to root of domain
3. Call firebase initializeApp
4. Call firebase getMessaging
5. Ask and approve browser notification permission
6. Add firebase onMessage listener
7. Call firebase await getToken(messaging, { vapidKey: <VAPID_KEY> })

Relevant Code:

const supported = await isSupported()
  if (!supported) {
      throw new Error(NOTIFICATIONS_NOT_SUPPORTED)
  }
  const messaging = getMessaging();
  const messagingToken = await getToken(messaging, {vapidKey})