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" onmouseover="over('mytd',200);" onmouseout="out('mytd',30);" style="background:#eee;">层的滑动展开/折叠</div>