js实现鼠标拖动图片并兼容IE/FF火狐/谷歌等主流浏览器

<script language="javascript" type="text/javascript">
var isDrag = false;
function isIE(){
if(navigator.userAgent.indexOf("MSIE")>0){return true;}
else{return false;}
}
function addListener(element,e,fn){
if(isIE()){element.attachEvent("on" + e,fn);}
else{element.addEventListener(e,fn,false);}
}
function drag(e){
var e = e || window.event;
var element = e.srcElement || e.target;
if(e.preventDefault)e.preventDefault();
else e.returnvalue=false;
isDrag = true;
var relLeft = e.clientX - parseInt(element.style.left);
var relTop = e.clientY - parseInt(element.style.top);
element.onmouseup = function(){ isDrag = false; }
document.onmousemove = function(e_move){
var e_move = e_move || window.event;
if(isDrag){
element.style.left=e_move.clientX - relLeft + "px";
element.style.top=e_move.clientY - relTop + "px";
return false;
}
}
}
window.onload = function()
{
var element = document.getElementById("elimg");
var element2 = document.getElementById("eldiv");
addListener(element,"mousedown",drag);
addListener(element2,"mousedown",drag);
}
</script>
<div id="eldiv" style="width:140px;height:100px;background:#EEE;position:absolute;left:117px;top:124px"></div>
<img id="elimg" style="left:609px;top:113px;position:absolute" src="http://www.cnit618.com/template/images/logo.gif" />