鼠标事件-拖拽

<!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>无标题文档</title>
<style>
#w{width:20px;height:20px;position:absolute;background:blue;}
</style>
<script>
window.onload=function(){

    var oDiv=document.getElementById("w");
    oDiv.onmousedown=function(ev){
        document.onmousemove=function(ev){
            var e=ev || event;    
            oDiv.style.left=e.clientX+"px";
            oDiv.style.top=e.clientY+"px";
        };
    };
    document.onmouseup=function(ev){//此处onmouseup触发事件需document触发，如换成div会造成无法接触onmousemove事件；
        document.onmousemove=null;    
    };    
};
</script>
</head>

<body>
<div id="w">
</div>
</body>
</html>