@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);
    }
}