自动关闭的层_典型特效

<script language="JavaScript1.2"> adTime=5; chanceAd=1; var ns=(document.layers); var ie=(document.all); var w3=(document.getElementById && !ie); adCount=0; function initAd(){ if(!ns && !ie && !w3) return; if(ie) adDiv=eval('document.all.sponsorAdDiv.style'); else if(ns) adDiv=eval('document.layers["sponsorAdDiv"]'); else if(w3) adDiv=eval('document.getElementById("sponsorAdDiv").style'); randAd=Math.ceil(Math.random()*chanceAd); if (ie||w3) adDiv.visibility="visible"; else adDiv.visibility ="show"; if(randAd==1) showAd(); } function showAd(){ if(adCount<adTime*10){adCount+=1; if (ie){documentWidth =document.body.offsetWidth/2+document.body.scrollLeft-20; documentHeight =document.body.offsetHeight/2+document.body.scrollTop-20;} else if (ns){documentWidth=window.innerWidth/2+window.pageXOffset-20; documentHeight=window.innerHeight/2+window.pageYOffset-20;} else if (w3){documentWidth=self.innerWidth/2+window.pageXOffset-20; documentHeight=self.innerHeight/2+window.pageYOffset-20;} adDiv.left=documentWidth-200;adDiv.top =documentHeight-200; setTimeout("showAd()",100);}else closeAd(); } function closeAd(){ if (ie||w3) adDiv.display="none"; else adDiv.visibility ="hide"; } onload=initAd; //End--> </script> <div id="sponsorAdDiv" style="visibility:hidden"> <table bgcolor="#008000"><tr><td> <table width="300" bgcolor="#F0FFF0"><tr><td align="center" valign="middle"> <p><b>欢迎光临网页教学网 有什么建议或意见请Mail给我， 非常感谢对本站的关注.</b> </p> <p>(该层将在5秒钟后自动关闭) </p> </td></tr></table> </td></tr></table> </div>
[Ctrl+A 全选 注:如需引入外部Js需刷新才能执行]