I’m trying to monitor which service workers are active (ie, which users have their browsers open). I came up with a solution that sends a simple ping through the web push API, and that would trigger the service worker to send a ping request to my server. But I’m finding that if I don’t display a notification to the user, I get an alert from Chrome.
This site has been updated in the background
Am I doing something wrong, or is there another way to solve this problem?
No, you're not doing anything wrong. This is by design.
It is not possible to contact the Service Worker in the background using the Web Push APIs and have the system not tell the user. You're describing a passive tracking system where you track the user even though the user is not using the product, and that has been restricted by SW design. When you use Web Push you should show your own notification (the API is for notifications) and if you don't, that's what the browser does.
I understand that it would be super nice to be able to contact the SW from the server and have it run some little errands but unfortunately that would make it possible to carry on some mischief too. You also cannot eg. leave open a WebSocket (not available in the SW) or schedule tasks in the future to have it ping (not guaranteed to run).