Issue 1933 - Cancellation of requests when no longer needed

[CaptainPants]

First attempt at #1933 - adding a cancellation mechanism to fetchers.

Looking for feedback on the approach and if there is any huge landmines I'm missing. I won't be offended if this is just a big 'no'.

Still working on how to appropriately test this.

TODO:

• Not sure how error handling works as this will cause the await to throw a DOMException from the abort call, and don't want this to send the hook into an error state.
• Testing.
• Tests - fix existing ones and add new ones related to the change.
• Add an example?

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[700software]

I would like for this feature to be enabled by default. Not the other way around.

Let's emphasize what the new users want rather than reverse compatibility since the risk of problems is low.

Would a new user who has no prior version of swr installed prefer this on by default or not? I think yes but I'm only one user.

[davidnormo]

Agreed

[steveluscher]

Lest setting this to true give someone a false impression, I think this config should be removed altogether.

1. Setting abortDiscardedRequests to true is insufficient for aborting discarded requests. Both of these also must be true
   a. The request API supports cancellation with AbortSignal (not all do)
   b. You remembered to pass the signal to that API
2. Simply ‘not passing the signal to the request API’ is sufficient to disable the cancellation of discarded requests.

I think we should not offer this config, but rather always pass signal to the fetcher function.

If you're worried about constructing a bunch of AbortControllers that nobody will ever use (don't) you could always create a Proxy and only construct the AbortController when someone gets the signal property.

[davidnormo]

Is there anything missing from this preventing it from being merged?

[oanaOM]

This would be very helpful to have! Any ideas when will this get released?
Meanwhile, is there other workaround to make SWR work with AbortController or achieve a cancelling mechanism?

[scarqin]

Exciting features! looking forward to launch.

[nikeee]

I'd omit an index signature because it may hide typos for the valid options (only signal in this case). It also prevents us from adding properties without introducing a potential breaking change.