Fallback to fetch() if the precached response is missing.

[jeffposnick]

R: @addyosmani @gauntface

This is the last 1/3 of #1188

If the browser doesn't have a cache match for a URL that should have been precached, this will cause it to go to the network instead of returning an error.

[gauntface]

Should we cache the file as well?

[jeffposnick]

Good question. The downside of caching is that we could end up in a state where we have a response cached that doesn't match the revision information inlined in the manifest/stored in IDB.

I don't know if that's preferable to having nothing cached at all.

One advantage to just logging rather than also attempting to "repair" the cache is that a developer who sees this message would know that their cache is in an inconsistent state. If we attempted to repair the cache but end up caching a different revision of a given URL, that won't end up logging anything the next time the same resource is requested, and the inconsistency would be hidden.

When implementing something similar in sw-precache, I just went with the network + logging route:

https://github.com/GoogleChromeLabs/sw-precache/blob/2ee24a96bb4812e83f47f6859361ba5e1bd535f5/service-worker.tmpl#L171-L176

[th3hunt]

Oh thank you!

After reading this about Safari,

To keep only the stored information that is useful to the user, WebKit will remove unused service worker registrations after a period of a few weeks. Caches that do not get opened after a few weeks will also be removed. Web Applications must be resilient to any individual cache, cache entry or service worker being removed.
https://webkit.org/blog/8090/workers-at-your-service/

I was looking for a workaround using some of the less popular workbox 2.x APIs.

Seeing this in v3 is a relief :)