code: function countdownTimer() {
      $(COUNTDOWN).html("0m 0s");
      var end_t = COUNTDOWNTIME;
      var start_t = (new Date()).getTime()/1000;
      function countdown() {
          var cur_t = (new Date()).getTime()/1000;
          var timeleft = (end_t - (cur_t - start_t));
          if (timeleft >= 0) {
              var min = Math.floor(timeleft / 60);
              var sec = Math.floor(timeleft % 60);
              $(COUNTDOWN).html(min + "m " + sec + "s");
              COUNTDOWNTID = setTimeout(countdown, 1000);
          } else {
              $.post("/games/" + enc($.cookie("game")) + "/players",
                     {end_turn: true}, function() {
                  getPlayers();
              });
          }
      }
      countdown();
  }
docs: Countdown timer. Update onscreen timer and end turn if time gets too low.