timer script using javascript

javascript timer

<script>
  function pretty_time_string(num) {
      return ( num < 10 ? "0" : "" ) + num;
    }

  var start = new Date;    

  setInterval(function() {
    var total_seconds = (new Date - start) / 1000;   

    var hours = Math.floor(total_seconds / 3600);
    total_seconds = total_seconds % 3600;

    var minutes = Math.floor(total_seconds / 60);
    total_seconds = total_seconds % 60;

    var seconds = Math.floor(total_seconds);

    hours = pretty_time_string(hours);
    minutes = pretty_time_string(minutes);
    seconds = pretty_time_string(seconds);

    var currentTimeString = hours + ":" + minutes + ":" + seconds;

    $('.timer').text(currentTimeString); //jQuery needed
  }, 1000);
</script>