gistfile1.txt

// A quick Javascript class for creating a countdown timer

// leadingZero is a boolean, onTimeCallback will be called on each second update with the timer string
function Countdown(hours,minutes,seconds, leadingZero, onTimeCallback) {
	this.hours = hours;
  this.minutes = minutes;
  this.seconds = seconds;
  this.countdownStr = hours+":"+minutes+":"+seconds;
  this.onTime = onTimeCallback;
  this.leadingZero = leadingZero;
}
Countdown.prototype.start = function() {
	this.countdownInterval = setInterval(function() {
  	this.seconds--;
    if (this.seconds==-1) {
    	this.seconds = 59;
      this.minutes--;
      if (this.minutes==-1) {
        this.minutes = 59;
      	this.hours--;
        if (this.hours==-1) {
        	this.stop();
        }
      }
    }
    
    if (this.leadingZero) {
    	this.countdownStr = (this.hours<10?"0"+this.hours:this.hours) + ":" +	(this.minutes<10?"0"+this.minutes:this.minutes) + ":" +	(this.seconds<10?"0"+this.seconds:this.seconds);
    }
    else {
    	this.countdownStr = this.hours+":"+this.minutes+":"+this.seconds;
    }
    this.onTime(this.countdownStr);
  }.bind(this), 1000);
}
Countdown.prototype.stop = function() {
	if (this.countdownInterval) clearInterval(this.countdownInterval);
}

/* Example use. prepare a div: <div id="countdown"></div> */
// var cd = document.getElementById('countdown');
// var countdown = new Countdown(5,11,17, true, function(timestr) { cd.textContent = timestr; } );
// countdown.start();