JavaScript Redirect Timer

<script type="text/javascript">
var waktu = 12;
setInterval(function() {
waktu--;
if(waktu < 0) {
window.location = 'http://URLTarget.tld';
}else{
document.getElementById("countdown").innerHTML = waktu;
}
}, 1000);
</script>


Pemanggil
<span id="countdown">10</span>