Js获取适时获取鼠标坐标值并显示

一个Javascript鼠标事件，适时获取屏幕指定区域任一点鼠标的X、Y坐标值，并利用JS输出出来，类似HOOK的功能，不明白的可以运行一下看看效果。

<title>Js获取适时获取鼠标坐标值并显示</title>
<script type="text/javascript">
  var getCoordInDocumentExample = function(){
    var coords = document.getElementById("coords");
    coords.onmousemove = function(e){
      var pointer = getCoordInDocument(e);
      var coord = document.getElementById("coord");
      coord.innerHTML = "X,Y=("+pointer.x+", "+pointer.y+")";
    }
  }
  var getCoordInDocument = function(e) {
    e = e || window.event;
    var x = e.pageX || (e.clientX +
      (document.documentElement.scrollLeft
      || document.body.scrollLeft));
    var y= e.pageY || (e.clientY +
      (document.documentElement.scrollTop
      || document.body.scrollTop));
    return {'x':x,'y':y};
  }
  window.onload = function(){
     getCoordInDocumentExample();
 };
</script>
<div id="coords" style="width:500px;height:200px;background:#F2F1D7;border:2px solid #0066cc;">
请在此移动鼠标。
</div>
<br />
<div id="coord" style="width:500px;border:2px solid #336699;">&nbsp;</div>