Future/promise vs JS generators

findOldestKnownFatherSideAncestor.js

function* findOldestKnownFatherSideAncestor(person) {
  let currentPerson = person;
  while (currentPerson.fatherId) {
    currentPerson = yield call(PersonAPI.getById,currentPerson.fatherId);
  }
  return currentPerson
}

findOldestKnownFatherSideAncestor.scala

def findOldestKnownFatherSideAncestor(person: Person): Future[Person] = {
  person.fatherId match {
    case None => Future(person)
    case Some(id) => PersonAPI.getById(id).flatMap(findOldestKnownFatherSideAncestor)
  }
}