<div id="box" style="background: black; width:100px; height:100px; position:absolute; left:0; top:0;"></div>
<script type="text/javascript">
var obj=document.getElementById("box");

window.onmousemove=function move(){

if(parseInt(obj.style.left)<event.pageX)
{
obj.style.left=parseInt(obj.style.left)+1;

}
if(parseInt(obj.style.top)<event.pageY){
obj.style.top=parseInt(obj.style.top)+1;
}
if(parseInt(obj.style.top)>event.pageY){
obj.style.top=parseInt(obj.style.top)-1;
}

if(parseInt(obj.style.top)>event.pageX){
obj.style.left=parseInt(obj.style.left)-1;
}

}
setInterval(move(),10);
</script>