Strategy unhandled rejection

[joshkel]

Fixes #3171

StrategyHandler.doneWaiting throws on the first rejected promise that it encounters. This means that subsequent rejected promises may result in unhandled rejection errors.

Promise.allSettled is a natural solution. It does not appear to be supported on all browsers that workbox uses. (However, I'm having trouble finding a clear statement of what browsers workbox supports, so I could be wrong.) I tried installing promise.allsettled from NPM but had trouble getting the default import from that module to work correctly with Rollup, and I noticed that the workbox service worker libraries tend to avoid external dependencies in general, so I created a local version instead. I put it under workbox-core's _private directory, following the example of other utility code such as Deferred. If I should handle this differently, please let me know.

This is a rebase of #3172 against the v7 branch.

[tomayac]

Fully approve of the intent of the PR. However, I don't think Promise.allSettled() needs polyfilling looking at browser support. Looking at devices that didn't make the Safari 13 cut, this are iPhone 5S, iPhone 6 and 6 Plus, the original iPad Air, the iPad mini 2 and iPad mini 3, and the 6th-generation iPod Touch. For Chromebooks, we'd be locking out Chromebooks stuck on Chrome <76. @tropicadri, what do you think?

[westonruter]

Fully approve of the intent of the PR. However, I don't think Promise.allSettled() needs polyfilling looking at browser support.

I'll note that Promise.allSettled() is now Baseline Widely available. So yeah, maybe no polyfill is needed?

[joshkel]

Thanks for the feedback, @westonruter (and @tomayac). Since Promise.allSettled is widely available, it seems like no polyfill is needed. However, making TypeScript happy with Promise.allSettled will require changing tsconfig.json's lib from es2017 to es2020. Is it okay to do that as part of this PR?

[westonruter]

@joshkel Yes, that makes sense to me, since Promise.allSettled() was introduced in es2020.

[joshkel]

@westonruter I've switched to the native version. Thanks again.

[westonruter]

I suppose the while loop needs to be retained in case additional promises are added to the array while awaiting the ones that were removed during the first iteration?

[joshkel]

Yes. (That was my rationale, at least.)

[westonruter]

On a related note, I just recalled that the Browser Support page indicates that only the current version minus 2 are to be supported. This is now clearly the case for Promise.allSettled()!