Observable Data Service

book-store-service.ts

@Injectable({
  providedIn: 'root'
})
export class BookStoreService {
  private _books = new BehaviorSubject<Book[]>([]);
  public readonly books$: Observable<Book[]> = this._books.asObservable();  

  constructor(private bookBackend: BookBackendService) {
    this.getBooks();    
  }

  addBook(newBook: Book): void {    
    this.bookBackend.addBook(newBook).subscribe((res) => {
      this._books.next(res);
    });
  }

  getBooks(): void {    
    this.bookBackend.getBooks().subscribe((res) => {
      this._books.next(res);
    });
  }  
}