AsyncPipe

异步管道订阅 Observable 或 Promise 并返回它发出的最新值。发出新值时，异步管道会标记要检查更改的组件。当组件被销毁时，异步管道会自动取消订阅以避免潜在的内存泄漏。

@Component({
  selector: 'async-observable-pipe',
  template: '<div><code>observable|async</code>: Time: {{ time | async }}</div>'
})
export class AsyncObservablePipeComponent {
  time = new Observable<string>((observer: Subscriber<string>) => {
    setInterval(() => observer.next(new Date().toString()), 1000);
  });
}