Given this Angular component code:

Given this Angular component code:

export class SampleComponent implements OnInit, OnDestroy {
  data$ = this.service.getData();
  subscription: Subscription | undefined;

  ngOnInit() {
    this.subscription = this.data$.subscribe(value => console.log(value));
  }

  ngOnDestroy() {
    this.subscription?.unsubscribe();
  }
}

What happens if ngOnDestroy does not unsubscribe?