Timer

HTML

<script src="https://code.jquery.com/jquery-2.2.4.min.js"></script>
<div class="js-timer">0:10</div>

JavaScript

function startTimer() {
  var timer = '0:10';
  var interval = setInterval(function () {
    timer = timer.split(':');
    var minutes = parseInt(timer[0], 10);
    var seconds = parseInt(timer[1], 10);
    seconds -= 1;

    if (seconds < 0 && minutes != 0) {
      minutes -= 1;
      seconds = 59;
    } else if (seconds < 10 && length.seconds != 2) {
      seconds = '0' + seconds;
    }

    if (minutes < 10 && minutes.length != 2) {
         minutes = '0' + minutes;
    }
    
    timer = minutes + ':' + seconds;
    $('.js-timer').text(timer);
    
    if (minutes <= 0 && seconds <= 0) {
      clearInterval(interval);
    }
  }, 1000);
}

function showPopup() {
  startTimer();
}

showPopup();