Call function immediately and every X seconds

Question

Using Angular 7 how to call function immediately and every X seconds? This is my function in service: (just as an example)

checkData(): Observable<string> {
    return this.http.get('')
        .pipe(
            map(res => {
                let result;
                result = {
                    packageNumber: this.packageNumber,
                };
                return result;
            })
        );
}

And in my component I tried something like this:

private killTrigger: Subject<void> = new Subject();
private fetchData$: Observable<string> = this.packageService.checkData();

private refreshInterval$: Observable<string> = timer(0, 1000)
    .pipe(
        takeUntil(this.killTrigger),
        switchMap(() => this.fetchData$),
        catchError(error => of('Error'))
    );

How to make it work?

I think you're looking for [interval](http://reactivex.io/rxjs/class/es6/Observable.js~Observable.html#static-method-interval) — Will, Nov 05 '18 at 14:36
`.interval(5000).startWith(0);` if I recall https://stackoverflow.com/questions/36612945/how-to-get-an-observable-to-return-data-immediately-and-every-5-seconds-thereaft — Will, Nov 05 '18 at 14:47
@ChrisK. If want to start emit without the initial delay use `timer` — martin, Nov 05 '18 at 14:52
@martin could you write an answer with an example of subscribe? — , Nov 05 '18 at 15:00
Yeah I didn't know timer but that looks better. Subscription is key. http://reactivex.io/rxjs/class/es6/Observable.js~Observable.html#instance-method-subscribe — Will, Nov 05 '18 at 15:02

Qortex · Answer 1 · 2018-11-12T11:32:17.127

You need to subscribe to it to launch it. Best way is to:

// class def
private subscription: Subscription;
// in NgOnInit
this.subscription = this.refreshInterval$.subscribe(noop)
// in NgOnDestroy
this.subscription.unsubscribe(); // avoid memory leaks

And to actually fire your fetchData$, you can replace your switchMap call by:

map(() => this.fetchData$.subscribe(noop),

If you don't subscribe to the observable, it never gets fired. Don't see why you would need switchMap here.

Call function immediately and every X seconds

1 Answers1