点击下载链接 弹出页面实现代码

<a
onclick=checkopen(this);
href="https://www.jb51.net"
target=_blank>打开下载页面1</a>
<script>
<!--
var original_url = ""
var adurl = new array(9);
var isclick = false;
var adurl_i = 5;
adurl[0] = "https://www.jb51.net";
adurl[1] = "http://www.yuanma51.com/";
adurl[2] = "http://www.baidu.com/";


function selectfrom(ifirstvalue,ilastvalue){
var ichoces = math.abs(ilastvalue - ifirstvalue) + 1;
return math.floor(math.random() * ichoces + ifirstvalue);
    }

adurl_i = selectfrom(0,2);

function checkopen(a){
if(adurl_i<9){
if(isclick==false){
original_url = a.href;    
a.href = adurl[adurl_i];
     isclick = true;
     top.location.href = original_url;    
     }else{
     a.href = original_url;
    }
}
}
//-->
</script>