Lior Levy's example for rxjs post

freeTextSerach.ts

  private searchQuery$ = new BehaviorSubject('');
  result$: Observable<string>; 

  ngOnInit(): void {
    this.result$ = this.searchQuery$.pipe(
      debounceTime(300), // will drop some values if they occur too frequently  
      switchMap(() =>this.service.fetchSomething(
        this.searchQuery$.getValue()) // will switch to the new inner observable when source emits and cancel the previus one
      )
    );
  }

  // The input component will use onChangeSearchText as handler for input changes  
  onChangeSearchText(freeText: string) {
    this.searchQuery$.next(freeText);
  }