<script language="javascript">
function teller(){
var getal = document.getElementById("afteller").innerHTML;
document.getElementById("afteller").innerHTML = getal - 1;
if(getal > 1)
window.setTimeout(teller, 1000);
}
</script>
<body onLoad="teller()">
<span id="afteller">20</span>
</body>
<script language="javascript">
function teller(){
var getal = document.getElementById("afteller").innerHTML;
document.getElementById("afteller").innerHTML = getal - 1;
if(getal > 1)
window.setTimeout(teller, 1000);
}
</script>
<body onLoad="teller()">
<span id="afteller">20</span>
</body>