Creating an already aborted AbortController

[jasnell]

In Node.js, we have had a couple of use cases pop up recently with the need to mark an AbortController already aborted immediately after creation. Typically, this would be done as: const ac = new AbortController(); ac.abort(); return ac;.

It would be helpful to have a utility that makes this easier...

Either:

const ac = new AbortController({ aborted: true });

or

const ac = AbortController.aborted();

The abort event would never trigger on such objects, which is perfectly fine. We already tell users to check the aborted property before attaching abort listeners.

If the idea seems reasonable, I can work up a PR with the change. I would just need to know which approach (init options vs. static factory function) is preferred.

[annevk]

Do you need an AbortController or an AbortSignal? AbortSignal.aborted() would make more sense to me.

cc @jakearchibald @domenic

[jasnell]

Good question... I think either would work for the immediate case to be honest.

[domenic]

I like AbortSignal.aborted(). I agree that the controller seems pretty useless if you've already aborted.

[domenic]

It'd be good to describe your use cases here, especially if you can expand them to be environment-agnostic so that people understand when they might also be applicable in web application code. That'd help make the pitch for multi-implementer interest.

[jasnell]

The most recent use case I've seen this for is the easiest/clearest... It's in the context of an HTTP request in Node.js:

1. An AbortController/AbortSignal is associated with an HTTP request.
2. The AbortController/AbortSignal is lazily created (that is, it is only created the first time it is explicitly asked for)
3. The HTTP request may already be aborted by the time the AbortController/AbortSignal is requested, in which case we want to just return an already aborted signal as opposed to undefined or throwing.

Very simple, and along the same lines as (for instance) Promise.reject().