abortcontroller-polyfill eventing isn't implemented properly

[benlesh]

I needed an AbortSignal/AbortController polyfill for work on RxJS, and I found out that the event dispatching in abortcontroll-polyfill (the recommended abort mechanism for this library) was not properly synchronous and didn't implement behaviors as they would actually exist in the wild. This is actually a big deal, as abort/cancellation should happen synchronously when abort() is called on the abort controller, and the order of events there is very important.

To that end, I started down the road of creating a PR for abortcontroller-polyfill, but: 1) I was almost rewriting the entire thing. and 2) That repository seemed to be somewhat stagnant and I needed a properly implemented one ASAP.

So I've created a new package called yet-another-abortcontroller-polyfill that aims to be accurate as possible when it comes to the semantics of the type and the events around it.

The problem I see is this is the defacto fetch polyfill, and if it has people polyfilling and using poorly implemented AbortSignals, it is going to break other things (like RxJS) in hard-to-explain ways for other users.

So I'd like to reconcile this somehow.

[benlesh]

NOTE: This issue was reported last year to the abortcontroller-polyfill repository here: mo/abortcontroller-polyfill#36

[JakeChampion]

@benlesh Thank you for raising this issue, I made a pull-request to update the readme to mention the polyfill you have written instead. Do you think that is ok? #814

[benlesh]

LGTM.