function stopwatch() {
        let time;
        let interval;
        let startButton = document.getElementById('startBtn');
        let stopButton = document.getElementById('stopBtn');
        startButton.addEventListener('click', () => {
            time = -1;
            interval = setInterval(incrementTime, 1000);
            incrementTime();
            startButton.disabled = true;
            stopButton.disabled = false;
        });
        stopButton.addEventListener('click', () => {
            clearInterval(interval);
            startButton.disabled = false;
            stopButton.disabled = true;
        });

        function incrementTime (){
            time++;
            document.getElementById('time').textContent =
                    ("0" + Math.trunc(time / 60)).slice(-2) +
                    ':' + ("0" + (time % 60)).slice(-2);
        }
    }