层的滑动展开/折叠

<script type="text/javascript">
var act;
function over(s,nMax){
var obj=document.getElementById(s);
var h = parseInt(obj.offsetHeight);
if (h < nMax){
obj.style.height = (h + 2)+"px";
clearTimeout(act);
act = setTimeout("over('"+s+"',"+nMax+")", 10);
}
}
function out(s,nMin){
var obj=document.getElementById(s);
var h = parseInt(obj.offsetHeight);
if (h > nMin){
obj.style.height = (h - 2)+"px";
clearTimeout(act);
act = setTimeout("out('"+s+"',"+nMin+")", 10);
}
}
</script>
<div id="mytd" οnmοuseοver="over('mytd',200);" οnmοuseοut="out('mytd',30);" style="background:#eee;">层的滑动展开/折叠</div>