Js鼠标跟随代码小手点击实例方法

<!DOCTYPE html PUBLIC "-//W3C//DTD XHTML 1.0 Transitional//EN" "http://www.w3.org/TR/xhtml1/DTD/xhtml1-transitional.dtd">
<html xmlns="http://www.w3.org/1999/xhtml">
<head>
<meta http-equiv="Content-Type" content="text/html; charset=utf-8" />
<title>可爱的鼠标跟随</title>
<style>
html{ background:#000;}
body,html,input{ cursor:none;}
body,html{ height:100%;}
#cursor{ position:absolute; left:100px; top:100px; display:block;}
</style>
<script>
 window.onload = function(){
  var oCursor = document.getElementById("cursor");
  document.onmousemove=function (ev){
   var oEvent=ev||event,
    oWidth = document.documentElement.clientWidth,
    oHeight = document.documentElement.clientHeight,
    scrollTop=document.documentElement.scrollTop + oEvent.clientY,
    scrollLeft=document.documentElement.scrollLeft + oEvent.clientX;
   if(scrollTop > oHeight-oCursor.offsetHeight){
    oCursor.style.top = oHeight-oCursor.offsetHeight+'px';
   }else if(scrollTop < 0){
    oCursor.style.top = 0;
   }else{
    oCursor.style.top = scrollTop+'px';
   }
   if(scrollLeft > oWidth-oCursor.offsetWidth){
    oCursor.style.left = oWidth-oCursor.offsetWidth+'px';
   }else{
    oCursor.style.left = scrollLeft+'px';
   }
   document.onmousedown = function(){
    oCursor.innerHTML = "<img src='//www.gxlcms.com/jscss/demoimg/201305/cursor_hover.png' />"; 
    return false;
   }
   document.onmouseup = function(){
    oCursor.innerHTML = "<img src='https://www.jb51.net/www.gxlcms.com/jscss/demoimg/201305/cursor.png' />"; 
   }
  };
 }
</script>
</head>
<body>
<img src="https://www.jb51.net/www.gxlcms.com/jscss/demoimg/201305/cursor.png" />
<input type="button" style="font-size:36px; margin:100px;" value="点击" onclick="window.open('//www.gxlcms.com')" />
</body>
</html>

[Ctrl+A 全选注:如需引入外部Js需刷新才能执行]