note.component.ts

export class AppComponent {
  note = new FormControl("");
  saveIndicator$: Observable<string>;
  saveCount = 0;

  ngOnInit() {
    const inputToSave$ = this.note.valueChanges.pipe(
      debounceTime(300),
      distinctUntilChanged(),
      share()
    );

    const savesInProgress$ = inputToSave$.pipe(
      mapTo(of("Salvando...")),
      tap(() => this.saveCount++)
    );

    const savesCompleted$ = inputToSave$.pipe(
      mergeMap(value => this.saveChanges(value)),
      tap(() => this.saveCount--),
      filter(() => !this.saveCount),
      mapTo(of("Salvo!"))
    );

    this.saveIndicator$ = merge(savesInProgress$, savesCompleted$).pipe(
      switchAll(),
      startWith("Todas as mudanças foram salvas")
    );

    inputToSave$.subscribe(console.log);
  }

  saveChanges(value: string) {
    return of(value).pipe(delay(1500));
  }
}