Angular 4: reactive form control is stuck in pending state with a custom async validator

There's a gotcha!

That is, your observable never completes...

This is happening because the observable never completes, so Angular does not know when to change the form status. So remember your observable must to complete.

You can accomplish this in many ways, for example, you can call the first() method, or if you are creating your own observable, you can call the complete method on the observer.

So you can use first()

UPDATE TO RXJS 6:

briteVerifyValidator(service: Service) {
  return (control: AbstractControl) => {
    if (!control.valueChanges) {
      return of(null);
    } else {
      return control.valueChanges.pipe(
        debounceTime(1000),
        distinctUntilChanged(),
        switchMap(value => service.getData(value)),
        map(data => {
          return data.status === 'invalid' ? { invalid: true } : null;
        })
      ).pipe(first())
    }
  }
}

A slightly modified validator, i.e always returns error: STACKBLITZ

---

OLD:

.map(data => {
   return data.status === 'invalid' ? { invalid: true } : null;
})
.first();

A slightly modified validator, i.e always returns error: STACKBLITZ