timeout.html

<span class="timeout">2:00</span>

<button id="startTimer">Start</button>

<script>
var interval;

function countdown() {
  clearInterval(interval);
  interval = setInterval( function() {
      var el = $('.timeout')
      var timer = el.html();
      timer = timer.split(':');
      var minutes = timer[0];
      var seconds = timer[1];
      seconds -= 1;
      if (minutes < 0) return;
      else if (seconds < 0 && minutes != 0) {
          minutes -= 1;
          seconds = 59;
      }
      else if (seconds < 10 && length.seconds != 2) seconds = '0' + seconds;

      el.html(minutes + ':' + seconds);

      if (minutes == 0 && seconds == 0) {
        clearInterval(interval); 
        // do other stuff when timeout
      }
  }, 1000);
}

$('#startTimer').click(function () {
  $('.timeout').text("2:00");
  countdown();
});
</script>