javacript问题

<STYLE>
    .vis1 { visibility:visible }
    .vis2 { visibility:hidden }
</STYLE>
<script>
var c=0
function f(b) {
c+=1;
var ss=setTimeout("f("+b+")","1000")if (c==b)
{
   clearTimeout(ss);
   document.all.div1.className="vis2";
}
}</script>
<body onload="f(5)">
<div id="div1">
<!--a href="http://bf.sina.com.cn/newbf/zt/06wy.html?from=400" target="_blank"><img src="http://image2.sina.com.cn/sms/ad/060427wyzt14862.GIF" style="border:#E71516 1px solid" WIDTH="148" HEIGHT="62"></a--><OBJECT style="border:#E71516 1px solid" classid="clsid:D27CDB6E-AE6D-11cf-96B8-444553540000" codebase="http://download.macromedia.com/pub/shockwave/cabs/flash/swflash.cab#version=5,0,0,0" WIDTH="148" HEIGHT="62" ID=ShockwaveFlash1>
<PARAM NAME=movie VALUE="http://image2.sina.com.cn/sms/ad/060430mqj148x62.swf"><PARAM NAME=quality VALUE=high>
<EMBED src="http://image2.sina.com.cn/sms/ad/060430mqj148x62.swf" quality=high WIDTH="148" HEIGHT="62" TYPE="application/x-shockwave-flash" PLUGINSPAGE="http://www.macromedia.com/shockwave/download/index.cgi?P1_Prod_Version=ShockwaveFlash"></EMBED>
</OBJECT>
</div>
</body>
<button onclick="" ID=Button1>开始</button>