Angular/RxJs When should I unsubscribe from `Subscription`

Question

When should I store the Subscription instances and invoke unsubscribe() during the NgOnDestroy life cycle and when can I simply ignore them?

Answer 1

--- Update Angular 9 and Rxjs 6 Solution

1. Using unsubscribe at ngDestroy lifecycle of Angular Component

class SampleComponent implements OnInit, OnDestroy {
  private subscriptions: Subscription;
  private sampleObservable$: Observable;

  constructor () {}

  ngOnInit(){
    this.subscriptions = this.sampleObservable$.subscribe( ... );
  }

  ngOnDestroy() {
    this.subscriptions.unsubscribe();
  }
}

2. Using takeUntil in Rxjs

class SampleComponent implements OnInit, OnDestroy {
  private unsubscribe$: new Subject;
  private sampleObservable$: Observable;

  constructor () {}

  ngOnInit(){
    this.subscriptions = this.sampleObservable$
    .pipe(takeUntil(this.unsubscribe$))
    .subscribe( ... );
  }

  ngOnDestroy() {
    this.unsubscribe$.next();
    this.unsubscribe$.complete();
  }
}

3. for some action that you call at ngOnInit that just happen only one time when component init.

class SampleComponent implements OnInit {

  private sampleObservable$: Observable;

  constructor () {}

  ngOnInit(){
    this.subscriptions = this.sampleObservable$
    .pipe(take(1))
    .subscribe( ... );
  }
}

We also have async pipe. But, this one use on the template (not in Angular component).