Pipe RxJS observable to existing subject, but not on completion

Question

I implemented an RxJS architecture based on the answer to this question: Pipe RxJS observable to existing subject

Later, I noticed that the observable randomly closed and I've spent a lot of time to find the cause. In the end, appeared that this snippet was causing the closing:

const delayed = Observable.of(arr.shift()).delay(1000);
merge(otherObs, delayed).subscribe(mySubject);

The of/delay observable was completing after 1 second, and it piped the completion to mySubject, making it unable to receive other values, including the ones sent by otherObs in case they arrived after the timeout.

Here is a StackBlitz that shows the problem.

How can I avoid mySubject completes, without explicitly writing the callbacks?

can you show your `otherObs` ? ... if it's not completed you would'nt receive the complete notification — bubbles, Sep 02 '20 at 15:39
@bubbles I don't think that seeing `otherObs` makes the difference, since it's the `delay` that completes. In my case, `otherObs` is a custom observable that never completes for sure, but you can imagine it as a timer if you prefer it for reproduction — Christian Vincenzo Traina, Sep 02 '20 at 15:49
from your stackblitz you're subscribing twice to the subject => This subject will complete on the first received complete notification (of, delay in your case) — bubbles, Sep 02 '20 at 16:14
I'm not subscribing twice, I'm piping twice. And I know that the first received complete will close it, this is what I want to avoid — Christian Vincenzo Traina, Sep 02 '20 at 16:15
`of(1).pipe(delay(1000)).subscribe(subject); interval(100).subscribe(subject);` they use the same subject — bubbles, Sep 02 '20 at 16:17
this code in the other hand will not terminate `const subject = new Subject(); subject.asObservable().subscribe(x => console.log(x)); merge(interval(100), of(1).pipe(delay(1000))).subscribe(subject);` — bubbles, Sep 02 '20 at 16:20

Rafi Henig · Accepted Answer · 2020-09-03T12:36:46.500

1

This is a known issue, as solution I would suggest extending Subject, to prevent its completion as long as there are others observers listening to it, as demonstrated below:

class RescrictedCompletionSubject<T> extends Subject<T>{

  public complete(): void {
    if (this.observers.length <= 1) super.complete();
  }
  
}

Optionally:

of(1).pipe(delay(1000)).subscribe(mySubject.next, mySubject.error);

Last but not least:

merge(otherObs, delayed).subscribe(mySubject);

edited Sep 03 '20 at 12:36

answered Sep 02 '20 at 16:27

Rafi Henig

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Thank you, this is exactly what I was looking for! Could you explain why `repeat` works without repeating the events? – Christian Vincenzo Traina Sep 03 '20 at 08:45
Can you add some external links to this *known issue* please ? For me this is the way `Subject` works – bubbles Sep 03 '20 at 08:54
`@bubbles` I didn't suggest it was a bug, nor that there was any thing wrong that needed to be fixed – Rafi Henig Sep 03 '20 at 11:58
`@Cristian Traìna` using `merge` there's no need for `repeat` operator, as it doesn't complete as long as there's at least one unclosed observable. – Rafi Henig Sep 03 '20 at 12:39
as apposed to subscribing directly [ `of(1).subscribe(mySubject);` ] which leads to `mySubject` completion – Rafi Henig Sep 03 '20 at 13:12

Pipe RxJS observable to existing subject, but not on completion

1 Answers1