What is the purpose of calling plete() on rxjs Subject?

As an example: Calling plete on takeUntil() notifier Observable. Why do we need to do that, and not just call next() and be done with it?

P.S. If it's just a convention, why is it so?

What is the purpose of calling plete() on rxjs Subject?

As an example: Calling plete on takeUntil() notifier Observable. Why do we need to do that, and not just call next() and be done with it?

P.S. If it's just a convention, why is it so?

• javascript
• rxjs
• observable
• subject

1 Answer 1

plete is normally called on subjects in order to send the pleted event through the stream. This is done in order to trigger observers that wait for that notification. For example:

var subject = new BehaviorSubject<int>(2);
var subjectStream$ = subject.asObservable();
var finalize$ = subjectStream$.pipe(finalize(()=> console.log("Stream pleted")));
var fork$ = forkJoin(subjectStream$,of(1));

....

finalize$.subscribe(value => console.log({value})); 
//output: 2, notice that "Stream pleted" is not logged.
fork$.subcribe(values => console.log({values}); 
// no output, as one of the inner forked streams never pletes

Furthermore, is a security measure in order avoid mem. leaks, as calling plete on the source stream will remove the references to all the subscribed observers, allowing the garbage collector to eventually dispose any non unsubscribed Subscription instance.