document.getElementByIdx_x=function(id){
if(typeof id =='string')
return document.getElementById(id);
else
throw new error('please pass a string as a id!')
}

<div id='box'>9</div>
<script>
document.getElementByIdx_x=function(id){
if(typeof id =='string')
return document.getElementById(id);
else
throw new error('please pass a string as a id!')
}
var timer = window.setInterval(function(){
document.getElementByIdx_x('box').innerHTML = parseInt(document.getElementByIdx_x('box').innerHTML) - 1;
if(parseInt(document.getElementByIdx_x('box').innerHTML) < 0)
{
window.clearInterval(timer);
window.location = 'http://www.phpstudy.net';
}
}, 1000);
</script>