Counterdown + RxJS

counterdown.ts

import { Observable, timer } from "rxjs";
import { map, takeWhile, take } from "rxjs/operators";

export function countdown(minutes: number, delay: number = 0) {
  return new Observable<{ display: string; minutes: number; seconds: number, finished: boolean }>(
    subscriber => {
      timer(delay, 1000)
        .pipe(take(minutes * 60))
        .pipe(map(v => minutes * 60 - 1 - v))
        .pipe(takeWhile(x => x >= 0 && !subscriber.closed))
        .subscribe(count => { // countdown => seconds
          const m = Math.floor(count / 60);
          const s = count - m * 60;

          subscriber.next({
            display: `${('0' + m.toString()).slice(-2)}:${('0' + s.toString()).slice(-2)}`,
            minutes: m,
            seconds: s,
            finished: m === 0 && s === 0
          });

          console.log('counter', count)

          if (s <= 0 && minutes <= 0) {
            subscriber.complete();
          }
        });
    }
  );
}
    
/**
Output:
{
    "display": "00:53",
    "minutes": 0,
    "seconds": 53,
    "finished": false
}
    
    
    */