button mit einem countdown

<script language="javascript">
var interval = window.setInterval ('countItDown()', 1000);
var sec = 5;

function countItDown()
{
document.getElementById('max').innerHTML = 'Button wird aktiviert in '+sec+' Sekunden';
sec--;

if (sec < 0 )
{
document.getElementById('mybutton').disabled = '';
clearInterval(interval);
}
}
</script>
<div id="max" style="font-family: verdana; font-size: 10px; color: #000099; font-weight: bold;"></div>
<input type="button" id="mybutton" value="Button" disabled="disabled">