How can i make a javascript timer?

Hi, i'm still new to javascript but how would i make a javascript coundown timer to countdown from a time length stored in php variable <?=$pt?> (for example 3:30 in minutes and seconds) and to start counting from the click of a button. and displays it in the specified div/anchor/input/ or any other tag through the tag's id or name.

So basiaclly a javascript timer that counts down from the time stored in <?=$pt?> on button click.

 

You can assign php variable to javascript like this var curr_time = <?=$pt?>;
and then you can use javascript date function to manipulate it.

http://www.quackit.com/javascript/javascript_date_and_time_functions.cfm

 

I knew this, but i need the code to countdown from the time stored in the variable in seconds and display each decrement.

 

Sorry, the last post was before visiting the link. Thanks.

 

I managed to write something close to what i wanted, but it's a count-up script rather than a count down. any way if you need it:

<script type="text/javascript">
var c=0;
var g=00;
var t;
var k=120;
var ir;
var d;
var h=60;
function timedCount()
{
document.getElementById('txt').value=d;
c=c+1;
ir=ir+1;
if(c<=h)
{
if(c<10) {d = g+":0"+c;}
else {d = g+":"+c;}
}
if(c>h)
{
g = g+1;
c=0;
}

t=setTimeout("timedCount()",1000);

}
</script>
</head>


<form>
<input type="text" id="txt">
<input type="button" onclick="timedCount()">
</form>

Code (markup):