RxJs: shareReplay() with cache invalidation after time

October 31, 2023

I want my shareReplay() to keep the value of a HttpService call (wsCall()) for a specific period of time. I often see samples like this on the web:

interval(10000).pipe(
    startWith(null),
    switchMap(_ => wsCall()),
    shareReplay()
);

The problem here is, that the webservice is called again every 10 seconds even if the Observable has no subscribers! Thats the internal behavior of shareReplay() – it subscribes and forwards the results.

But how to (easily) achieve what I’m looking for?

>Solution :

Use the underlying share operator instead of shareReplay

interval(10000).pipe(
    startWith(null),
    switchMap(_ => wsCall()),
    share({
      connector: () => new ReplaySubject(1),
      // this next line causes it to stop the interval if
      // no one is subscribed for more than 5 seconds
      resetOnRefCountZero: () => timer(5_000),
      resetOnError: false,
      resetOnComplete: false,
   }),
);