countdown with rx

countdown.rx.js

const now = moment();
const end = now.clone().add(2, 'minutes');
const diff = (end - now) / 1000;

const tick$ = Rx.Observable.timer(0,1000)
  .scan((acc) => {
    return acc - 1;
  }, diff)
  .take(diff);

tick$.subscribe((v) => console.log(v));