javascript countdown 1 minute

<script>
        function startTimer(duration, display) {
            var timer = duration, minutes, seconds;
            setInterval(function () {
                minutes = parseInt(timer / 60, 10);
                seconds = parseInt(timer % 60, 10);

               // minutes = minutes < 10 ? "0" + minutes : minutes;
                seconds = seconds < 10 ? "0" + seconds : seconds;

                display.textContent =  seconds;

                if (--timer < 0) {
                    timer = duration;
                }
            }, 1000);
        }

        window.onload = function () {
            var fiveMinutes = 60 * 5,
                display = document.querySelector('#time');
            startTimer(fiveMinutes, display);
        };
    </script>
   
<span id="time"></span>