Looks like the only way to get to this state is when the service worker terminates -
https://cs.chromium.org/chromium/src/third_party/WebKit/Source/modules/cachestorage/CacheStorage.cpp?l=235
But that does not make a lot of sense here (it is calling the code... Or maybe it is calling the code exactly when Chrome terminates it? But then you will not have a scripting execution environment to know about that, since it has terminated, I guess).

I've tried to get into that state but it isn't easy. Seems like an edge case. I've tried incognito and disabling my cache but no go. Maybe there is deeper place in the settings to disable cache that I'm not familiar with?

Would you mind providing us a sample test case for the ease of finding regression?

Investigating...

I don't see how this could happen. Could you share any example code?

CacheStorage::open returns a ScriptPromise which would have a .then method.

In the error case phistuck@ mentioned, when we return an empty ScriptPromise, the effect in JS-land would be to return undefined. So the error message would be "Cannot read property 'then' of undefined".

Anymore feedback or clues would be appreciated.

I realize this is a different issue, but perhaps the fix is related - see  issue 617539 .

Yeah, that looks like an unrelated problem/fix. I suspect something is wrong with the script... pedro@ are you sure the value directly returned by caches.open() is an Object without a .then method? Are you using any intermediate libraries or code to invoke caches.open()?

Please re-open if there is a repro or strong clues on how to repro.