一个简单的滑动时间问题

<head>
<style type="text/css">
.tr2{filter:alpha(opacity=0);}
</style>
<script language="javascript">
var timer=null;
function yc()
{
    if(tr2.filters.alpha.opacity<=0)
    trShow();
else
    trHide();
}
function trShow(){
tr2.filters.alpha.opacity = tr2.filters.alpha.opacity + 3;
if(tr2.filters.alpha.opacity<100){
timer = setTimeout("trShow()",1);
}
}
function trHide(){
tr2.filters.alpha.opacity = tr2.filters.alpha.opacity - 3;
if(tr2.filters.alpha.opacity>0){
timer = setTimeout("trHide()",1);
}}
</script>
</head>
<body>
<table id=tb width="100%"  border="1" cellspacing="1" cellpadding="1">
  <tr id=tr1  onclick="yc()">
    <td height="30" width="100%">1</td>
  </tr>
  <tr >
    <td id=tr2 class="tr2"  height="30"  >2222222222222222222222222</td>
  </tr>  
</table></body>