问Angular / RxJS:如何生成延迟值序列？

EN

import { Observable } from 'rxjs/Observable';
import { fromArray } from 'rxjs/observable/fromArray';
import 'rxjs/add/operator/delay';


@Injectable({
  providedIn: 'root'
})
export class MessageService {

  constructor() { }

  getIncomingMessagesStream(): Observable<string> {
    const messageTimeout = 2000;

    const messages = ['Hi there!', 'How are you?', 'That is awesome :)'];

    return fromArray(messages)
      .delay(messageTimeout);
  }
}

messageService.getIncomingMessagesStream()
    .subscribe(message => console.log('New incoming message ', message) );