Angular 2 polling with RxJS

问题

I'm trying to poll a RESTful endpoint to refresh my live chat messages. I know the best approach for a live chat would be Websockets, I'm just trying to understand how RxJS works with Angular 2.

I want to check for new messages every second. I have the following code:

return Rx.Observable
   .interval(1000)
   .flatMapLatest(() => this.http.get(`${AppSettings.API_ENDPOINT}/messages`))
   .map(response => response.json())
   .map((messages: Object[]) => {
      return messages.map(message => this.parseData(message));
   });

However my Typescript transpiler is returning this error:

Property 'flatMapLatest' does not exist on type 'Observable<number>'

I'm using RxJS 5.0.0-beta.0

If I use merge instead of flatMapLatest it doesn't call the API at all.

回答1:

You need to use switchMap(), there's no flatMapLatest() in RxJS 5.

See Migrating from RxJS 4 to 5... Although docs aren't very clear about switchMap()...

Returns a new Observable by applying a function that you supply to each item emitted by the source Observable that returns an Observable, and then emitting the items emitted by the most recently emitted of these Observables.

回答2:

To explain @Sasxa 's answer a bit more.

SwitchMap in illustration. (from http://reactivex.io/documentation/operators.html)

来源：https://stackoverflow.com/questions/35010182/angular-2-polling-with-rxjs