CODEWITHSUNDEEP
angularrxjs
rudrasiva86
rudrasiva86

Reputation: 583

What is the difference between the unsubscribe() method in Subject and Subscription class?

I subscribed to a Subject using the subscribe() method on the Subject class. To unsubscribe I see two options, since the unsubscribe() method is available on both Subject and Subscription classes.

  1. use the Subscription which is returned by subject.subscribe() method
ngOnInit() {
  this.subscription = this.subject.subscribe(next => nextHandler(), err => errHandler()); 
}

ngDestroy() {
  this.subscription.unsubscribe();
}
  1. Call unsubscribe() method directly on the subject like subject.unsubscribe()
ngOnInit() {
  this.subject.subscribe(next => nextHandler(), err => errHandler()); 
}

ngDestroy() {
  this.subject.unsubscribe();
}

What is the correct way of unsubscribing.

Upvotes: 5

Views: 850

Answers (2)

haridevelops
haridevelops

Reputation: 35

Assume Subject as a News Paper which will send you a stream of events every day and subscription is related to users subscription.

Subject.unsubscribe() When you do this, you actually want to destroy the newspaper itself, you should not be doing that. Subscription.unsubscribe() When you do this, you are just unsubscribing the subscription to which you have subscribed. not the source(Subject).

See the demo below: https://stackblitz.com/edit/typescript-umf1tv

Upvotes: 2

martin
martin

Reputation: 96891

The only difference I'm aware of is that when using Subject.unsubscribe() it won't trigger any dispose handlers created by piping operators.

import { Subject } from 'rxjs'; 
import { finalize } from 'rxjs/operators';

const subject = new Subject();

const subscription = subject
  .pipe(
    finalize(() => console.log('done')),
  )
  .subscribe();

subject.unsubscribe();
// subscription.unsubscribe();

This will never print done to the console because Subject.unsubscribe() only removes all observers. https://github.com/ReactiveX/rxjs/blob/master/src/internal/Subject.ts#L105

While using subscription.unsubscribe() will trigger finalize's dispose handler which is probably the more predictable behavior.

Live demo: https://stackblitz.com/edit/rxjs-z5fjh1

Upvotes: 4

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