pwa-update-available | Service Workers - New Update Available sample

the service worker registration routine you have only triggers when you index.html is loaded in the browser. It is the only time that code is executed.

Unless you periodically poll your server or possibly open a websocket (sort of expensive just for this) you wont know if a new service worker is available. You could have the user register for push notifications....too much headache for this.

So pool the server every few hours or days for an update.

If there is an update you can trigger an update routine.

I would put the polling logic in the actual service worker code to keep it off the UI, if you are a SPA you are already locking the UI thread enough LOL.

There are lots of ways to skin this cat, setTimeout(..., {lots of seconds}), when the service worker wakes from being dormant, etc.

If you can make a HEAD request that would keep the network traffic to a minimum.

If there is an update you could then post a message to the UI to update the service worker.

This is not what I would call trivial code. I do similar stuff to keep my cached assets up to date, so I have been there :)