Is it possible to make a function in angular / typescript that could return a Promise if it had .then or Observable called when it was subscribed?

Question

Angular

Is it possible to make a universal function that would return a promise if .then() is launched on it or Observable if it is subscribed to or not, but is it better not to bother and write 2 different functions?

Answer 1

It is possible to write a function that always returns an Observable. If you need to get a promise - just wrap the function call in `firstValueFrom` or `lastValueFrom` from rxjs.
What you originally wrote can be solved with an extended Observable, something like (pseudocode)

class ObservableWithThen extends Observable {
  then(cb) {
    return firstValueFrom(this).then(cb);
  }
}

And in the function, instead of the usual Observable, create and return ObservableWithThen