timer timer timer

timer.js

class Timer {
  constructor(duration) {
    const initDuration = (duration || 1) * 60;
    
    this.initDuration = initDuration;
    this.duration = initDuration;
    this.intervalId = -1;
    this.interval = 1000;
    this.displayDuration = `${duration}:00`;
  }
  
  run() {
    this.intervalId = window.setInterval(() => {
      
      let minutes = parseInt(this.duration / 60, 10);
      let seconds = parseInt(this.duration % 60, 10);
      
      minutes = minutes < 10 ? `0${minutes}` : minutes;
      seconds = seconds < 10 ? `0${seconds}` : seconds;
      
      this.displayDuration = `${minutes}:${seconds}`;
      
      console.log(this.displayDuration);
      
      this.duration--;
      
      if (this.duration < 0) {
        window.clearInterval(this.intervalId);
      }
    }, this.interval);
  }
  
  cancel() {
    window.clearInterval(this.intervalId);
  }
  
  reset() {
    this.duration = this.initDuration;
    this.intervalId = -1;
    this.displayDuration = `${this.duration}:00`;
  }
}

const t = new Timer(1);

t.run();

setTimeout(() => t.cancel(), 2000);