search.ts

  constructor(private http: HttpClient) {
      this.bookStore.observeQuery().pipe(filter(Boolean),
        debounceTime(200),
        distinctUntilChanged(),
        tap(async (query: string) => {
          const bo: Observable<Book[]> = this.searchAPI(query);
          const books: Book[] = await bo.toPromise();
          this.bookStore.reset();
          this.bookStore.postA(books);
        })
      )
      .subscribe();
  }