Proposal: Allow Promise callbacks to be removed

[Oliver Dunk]

My proposal is that we add a way of removing a particular callback, or all callbacks, from a Promise. This is different to cancelling a Promise and would instead happen if you want the operation to continue but are no longer interested in running a function when the Promise is resolved or rejected.

This would be implemented in two ways. The first I believe to be most useful, and the second is a sort of “sub-proposal”, that I would be happy to leave out:

1. A new `Promise.prototype.clear()` method. This would remove all callbacks currently added to a Promise.
2. A `Promise.prototype.clear(promise)` method, which takes the Promise returned when `Promise.prototype.then()` or `Promise.prototype.catch()` was called. This would remove that specific callback leaving any others. I don’t know if another argument would make better sense here? Maybe an identifier to the one used in `clearInterval()`.

The use case that I see for this is for a Promise equivalent to `EventTarget.removeEventListener()`.

I look forward to hearing feedback on this. I am new to the process here and so am open to any advice and am happy to make changes on this if there is an approach that would be considered better practice.