Cancelable promises

[pburtchaell]

Cancelable Promises have advanced to stage 1 at TC39. I'm creating this issue as a reminder that the middleware will need to be upgraded in the future to support this (if it becomes a part of the spec).

I imagine the middleware will simply dispatch a third action type, e.g., FOO_ACTION_CANCELLED.

Reminder: stage 1 is a feature "worth working on" so cancelable promises are speculative.

[tomatau]

Yeh the CANCELLED action type sounds perfect

[steida]

No, it's a terrible idea. Cancelling is another kind of rejection. Such change would introduce the whole universe of brittleness.

[pburtchaell]

No, it's a terrible idea. Cancelling is another kind of rejection.

From the proposal: "canceled is a third state, alongside fulfilled and rejected."

[steida]

And that's exactly what is wrong. It's completely against the promises principle. Hey, imagine you gave a promise to somehow. It can be resolved or rejected. Canceling is a lie in the contract.

[tomatau]

One of the major problems with promises is that they can't be cancelled. This is why many people have turned to observables.

Cancelling is a state that is decided by the consumer of the promise, not by the promise itself (such as rejected). This is a great way to avoid things like DOM updates as a result of the promise when the necessary nodes were unmounted between the promise being started and being resolved.

Cancelling is good and does not introduce brittleness.

The only concern I can think of is when there are multiple consumers of a promise. But if they all handle the cancelled state appropriately, then it should be fine.

[pburtchaell]

This proposal has been withdrawn. Closing the issue.