Is there a way to implement (x: Promise>): AsyncIterableIterator in TypeScript?

Question

So I get Promise<AsyncIterableIterator<T>> and I need plain AsyncIterableIterator<T> how can I unwrap the AsyncIterableIterator<T> from under the promise?

Answer 1

Yes, it's actually quite simple. We want to implement the AsyncIterableIterator interface ourselves, and for every call to next we first unwrap the Promise.

function unwrapAsyncIterableIteratorPromise (input) {
  return {
    next (value) {
      return input.then((iterator) => iterator.next(value))
    },
    [Symbol.asyncIterator] () {
      return this
    }
  }
}

It's also on npm together with TypeScript typings:

https://www.npmjs.com/package/unwrap-async-iterable-iterator-promise