Countdown Time JavaScript

An example of Countdown Time JavaScript

var _countDowncontainer=0;
var _currentSeconds=0;

function ActivateCountDown(strContainerID, initialValue) {
_countDowncontainer = document.getElementById(strContainerID);

if (!_countDowncontainer) {
alert("count down error: container does not exist: "+strContainerID+
"\nmake sure html element with this ID exists");
return;
}

SetCountdownText(initialValue);
window.setTimeout("CountDownTick()", 1000);
}

function CountDownTick() {
if (_currentSeconds <= 0) {
alert("your time has expired!");
return;
}

SetCountdownText(_currentSeconds-1);
window.setTimeout("CountDownTick()", 1000);
}

function SetCountdownText(seconds) {
//store:
_currentSeconds = seconds;

//get minutes:
var minutes=parseInt(seconds/60);

//shrink:
seconds = (seconds%60);

//get hours:
var hours=parseInt(minutes/60);

//shrink:
minutes = (minutes%60);

//build text:
var strText = AddZero(hours) + ":" + AddZero(minutes) + ":" + AddZero(seconds);

//apply:
_countDowncontainer.innerHTML = strText;
}

function AddZero(num) {
return ((num >= 0)&&(num < 10))?"0"+num:num+"";
}