注意是用到了，下列的演示
<script language="JavaScript" type="text/javascript">
adTime=8;
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-100;adDiv.top =documentHeight-0;
        setTimeout("showAd()",100);}
}
function closeAd(){
if (ie||w3)
adDiv.display="none";
else
adDiv.visibility ="hide";
}
function $(obj){
    return document.getElementById(obj);
}

function checkForm(){
    if($("file1").value != "")
    {
                if(/jpg|jpeg|gif|bmp/i.test($("file1").value.match(/\.(\w+)$/)[0]) == false){
                    alert("您只能上传图片文件");
                    return false;
                }
                else
                {
                    return true;
                }
    }
    else
    {
        alert("您还没有选中需要上传的图片");
        return false;
    }
}
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