FCM - Upgrading service worker code to Firebase 9

Question

The FCM doc shows how to handle background messages with Firebase 9 but the examples for Firebase 9 uses import which as far as I understand is not supported in service workers. The Firebase 8 example correctly uses ImportScripts.

I have tried using ImportScripts for Firebase 9:

importScripts('https://www.gstatic.com/firebasejs/9.1.2/firebase-app.js');
importScripts('https://www.gstatic.com/firebasejs/9.1.2/firebase-messaging.js');

Both paths exist, but in my app I get an error

The script at 'https://www.gstatic.com/firebasejs/9.1.2/firebase-app.js' failed to load.

Can anyone show some code of a working version of a service worker using Firebase 9 to handle background message?

Note: the doc on how to add Firebase to a web project says

Reserved Hosting URLs are available only with version 8 and earlier. You cannot use version 9 or later with Hosting URLs.

Which would explain why the ImportScripts doesn't work but how to proceed then?

Answer 1

Use the following imports:

importScripts('https://www.gstatic.com/firebasejs/9.5.0/firebase-app-compat.js')
importScripts('https://www.gstatic.com/firebasejs/9.5.0/firebase-messaging-compat.js')

These are compatibility versions of v9 which should support the other existing code within the file.