Angular 4 - Loopback 2“内部服务器错误”“对象（...）不是函数”

Question

我不知道为什么会出现这个错误，我按照角色英雄之旅教程

代码：

public productsURL = 'http://localhost:3000/api/productos';  // URL to web api

  constructor(
    private http: HttpClient,
    private messageService: MessageService) { }

  getProducts (): Observable<Product[]> {
    return this.http.get<Product[]>(this.productsURL)
      .pipe(
        tap(products => this.log(`fetched heroes`)),
        catchError(this.handleError('getProducts', []))
      );
  }