JavaScript实现层展开与关闭的动画效果

<!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>层展开、关闭</title>
<style type="text/css">
#main{
width:500px; margin:100px;
height:500px;border:1px solid red
}
#test{
border:1px solid red;
display:none;width:10px;
height:10px; background:yellow
}
</style>
</head>
<body>
<input type="button" value="打开" id="bt" />
<input type="button" value="关闭" id="bt1" />
<div id="main"><div id="test"></div>
</div>
</body>
</html>
<script type="text/javascript">
function $ (o) {
return document.getElementById(o);
}
function XslideDown(obj,type,mX,num) {
if(!type){return;}
try{
var type1=type=="height"?"marginTop":"marginLeft";
var type2=type=="height"?"top":"left";
XSetCss(obj,[type1,XgetOffset(obj)[type2]+"px"]);
XSetCss(obj,[type,XgetOffset(obj)[type]+num+"px"]);
if(XgetOffset(obj)[type]<mX){
setTimeout(function(){XslideDown(obj,type,mX,num);},10); 
}
else{
XSetCss(obj,[type,mX])
}
}
catch(e){}
}
function XslideUp(obj,type,mX,num) {
if(!type){return;}
try{
var type1=type=="height"?"marginTop":"marginLeft";
var type2=type=="height"?"top":"left";
XSetCss(obj,[type1,XgetOffset(obj)[type2]+"px"]);
XSetCss(obj,[type,XgetOffset(obj)[type]-num+"px"]);
if(XgetOffset(obj)[type]>mX){ 
setTimeout(function(){XslideUp(obj,type,mX,num);},1); 
}
else{
XSetCss(obj,[type,mX])
obj.style.display="none";
}
}
catch(e){}
}
function XSetCss(obj,cssArgs){
if(arguments.length==2)
{ 
if(cssArgs.constructor==Object){
for(var o in cssArgs)
{
if(obj.style[o]!="undefiend")
{
obj.style[o]=cssArgs[o]; 
} 
} 
}
if(cssArgs.constructor==Array&&cssArgs.length==2){
obj.style[cssArgs[0]]=cssArgs[1]; 
}
}
}
function XgetOffset (obj) {
return {
height:obj.offsetHeight,
width:obj.offsetWidth,
top:parseInt((obj.parentNode.offsetHeight-obj.offsetHeight)/2),
left:parseInt((obj.parentNode.offsetWidth-obj.offsetWidth)/2)
}
}
function XopenDiv(o){
o.style.display="block";
XslideDown(o,"width",400,10);
XslideDown(o,"height",400,10);
}
function XcloseDiv(o){
XslideUp(o,"width",10,10);
XslideUp(o,"height",10,10);
}
$("bt").onclick=function(){
XopenDiv($("test"))
}
$("bt1").onclick=function(){
XcloseDiv($("test"))
}
</script>