RxJs Interval with takeUntil to publish last value - angular6

Question

I have some code which polls until a task is complete
See below
this.simulationStatus =
interval(2000).pipe(
switchMap(
() => from(this.simulationService.getSimulationStatus(this.route.snapshot.paramMap.get('jobId')))),
takeUntil(this.stopPoll),
tap(simulation => {
if (simulation && simulation.complete) {
if (this.stopCount == 1) {
// Get once after complete
this.stopPoll.next(true);
}
this.stopCount++;
}
})
);
I have tried using takeUntil and takeWhile the problem is that that the last value is never published once the task is complete.
To get around this I have to include the tap method to with the stopPoll subject and incrementing the stopCount to get the last value.
So the above works but just feels a bit messy, I'm sure there must be a better way of achieving this?
I would have expected takeUntil to publish the last value or have an override to tell it to e.g takeUntil(observable, {publishLast: true})
BTW Update, the observable is subscribed to by an Angular 6 template
Thanks in advance

Answer 1

One thing you can do is use a custom takeWhile-like operator like this:
const completeWith = <T>(predicate: (arg: T) => boolean) => (
source: Observable<T>,
) =>
new Observable<T>(observer =>
source.subscribe(
value => {
observer.next(value);
if (predicate(value)) {
observer.complete();
}
},
error => observer.error(error),
() => observer.complete(),
),
);
It doesn't seem like a good idea to see it as a variation of takeWhite because it's not just taking values while a condition holds, but also emits an extra value.
It might be that a more elegant solution would be make the simulation status observable emit two kinds of values: next notifications and completion notifications, similarly to how materialize/dematerialize operators work.

Answer 2

This has in the meantime been implemented in rxjs as takeWhile(condition, ?inclusive):
timer(0, 10).pipe(
takeWhile((x) => x < 3, true)
)
emits 0, 1, 2, 3

Answer 3

You can also create subject and emit using next() if you want to complete the observable.
this.stopPoll: Subject<any> = new Subject<any>();
If you want to do complete the subscription. you can call this.stopPoll.next(true);
you can access the data in subscribe()
this.simulationStatus.subscribe(success=>{}, failure=>{}, complete=>{});