View difference between Paste ID: VVzzcJWY and AV1zdAr1

 @Component({})
 export default class Question extends Vue {
     questionTimer: Timer = new Timer(30);
 
     startQuestionTimer() {
         this.questionTimer.startTimer();
     }
 }
 export class Timer {
     duration;
     timeLeft: string;
     isTimerActive: boolean;
 
     constructor(duration: number) {
         this.duration = duration;
     }
 
     startTimer() {
         this.isTimerActive = true;
         let minutes, seconds, timer = this.duration;
         let interval = setInterval(() => {
             if (!this.isTimerActive) clearInterval(interval)
             minutes = Math.floor(timer / 60);
             minutes = minutes < 10 ? "0" + minutes : minutes;
             seconds = timer % 60;
             seconds = seconds < 10 ? "0" + seconds : seconds;
             this.timeLeft = minutes + ":" + seconds;
 
             if (--timer < 0) {
                 this.isTimerActive = false;
                 clearInterval(interval);
             }
         }, 1000);
     }
 }