[If changing import() proves not backwards compatible] Alternative proposal

[Jamesernator]

This proposal currently depends on the fact that changing import() is backwards compatible. However if it proves not to be I would like to propose an alternative that delegates the un-thening to the producer rather than the consumer.

The proposal is very simple: just add a an internal slot to promise instances [[OriginalResolveValue]] that is the value that was originally passed into resolve. Then we could have a single static function on Promise, e.g. Promise.originalValue that returns a new promise that boxes the [[OriginalResolveValue]].

e.g.:

const thenable = {
  then() {
    throw new Error("Oh dear")
  },
}

const promise = Promise.resolve(thenable)

const unwrappedPromise = Promise.originalValue(promise)

const { value: originalThenable } = await unwrappedPromise

originalThenable === thenable // true

The main downside is that .then() would still be invoked but this means it wouldn't be a breaking change for existing code.

[ljharb]

It should not be possible to do this unless the promise has explicitly opted in; i can think of all sorts of security issues/encapsulation violations that would occur. If it can’t be done on the producing end it probably shouldn’t be done.