javascript - 如何避免第一个未定义的订阅 JavaScript RxJS

Question

我想订阅从服务器获取的一些对象。但是第一次的代码没有给我任何返回。订阅的代码:

ngOnInit() {
    this.dataService.getEvents()
    .subscribe(
    (events) => {
      this.events = events;  
      console.log(events);   // when I try to get this is no problem it prints log to console (probably because event is var so it is not defined)  
      console.log(events[0].name); // it didn't see that property so I'm getting ERROR TypeError: Cannot read property 'name' of undefined          
    });        
  }

服务看起来像这样，我正在为 Observable 使用 BehaviorSubject:

 private eventChanged = new BehaviorSubject<any>([]);

  constructor(private http: HttpClient) { 
    this.refetch();
  }
  private refetch(): void {
    this.http.get<EventE[]>(this.baseUrl)
      .subscribe(events => {
        this.events = events;
         this.eventChanged.next(events);
      });
  }

  getEvents(): Observable<any> {
    return this.eventChanged.asObservable();
  }

如何避免此错误并只订阅已定义的事件

Answer 1

我只想添加一个过滤器来排除初始订阅中的未定义事件:

ngOnInit() {
    this.dataService.getEvents()
    .filter(events => events && events.length > 0)
    .subscribe(
    (events) => {
      this.events = events;  
      console.log(events);   // when I try to get this is no problem it prints log to console (probably because event is var so it is not defined)  
      console.log(events[0].name); // it didn't see that property so I'm getting ERROR TypeError: Cannot read property 'name' of undefined          
    });        
  }