import { interval, fromEvent } from 'rxjs';
const COUNTDOWN_TIME = 10;
const countdownElem = document.getElementById('countdown');
const click$ = fromEvent(document, 'click');
const countdown$ = interval(1000).pipe(
scan((acc, _) => --acc, COUNTDOWN_TIME),
startWith(COUNTDOWN_TIME)
takeWhile(val => val >= 0),
finalize(() => (countdownElem.innerHTML = "We're done here!"))
.subscribe((val: any) => (countdownElem.innerHTML = val));