016 - Call hook at intervals

import {timer, isObservable, of} from "rxjs";
import {share, switchMap} from "rxjs/operators";

function callHook$(hook$, freq) {
    const _hook$ = isObservable(hook$) ? hook$ : of(hook$);
    // freq must be int
    let _freq = Math.round(freq);

    return _freq > 0
        // share will kill the timer when no subscribers are left
        ? timer(0, Math.max(1000, _freq)).pipe(share(), switchMap(() => hook$))
        : hook$;
}