Re: [ServiceWorker] should update on navigation or the subsequent updatefound event be delayed until document DOM is loaded? (#788)

I'm not against delaying the update a bit for performance reasons (or at least suggest it can be low priority), but I don't think it fixes the original issue.

Imagine:

* Functional event lands in SW
* More than 24hrs since update, so update triggered, updated SW found, becomes installing
* User navigates to in-scope page
* "updatefound" listener added
* Update triggered, SW is byte identical so it's ignored
* SW moves from "installing" to "installed"

Even with the delay, the listener misses the new SW. The only safe way know when a SW becomes installed is to listen for "updatefound" but also track any current `reg.installing`. Eg https://github.com/jakearchibald/wittr/blob/cache-avatars/public/js/main/IndexController.js#L45.

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https://github.com/slightlyoff/ServiceWorker/issues/788#issuecomment-173606879