同一IP只弹一次窗口的代码

限制一个IP只弹窗一次的页面广告代码：

<SCRIPT language="JavaScript">
<!--
function openpopup(){
url="http://www.downcodes.com/"
window.open(url,"www.downcodes.com","width=300,height=150,left=400,top=50")
}

function get_cookie(Name) {
var search = Name + "="
var returnvalue = "";
if (document.cookie.length > 0) {
offset = document.cookie.indexOf(search)
if (offset != -1) {
offset += search.length
end = document.cookie.indexOf(";", offset);
if (end == -1)
end = document.cookie.length;
returnvalue=unescape(document.cookie.substring(offset, end))
}
}
return returnvalue;
}

function helpor_net(){
if (get_cookie('popped')==''){
openpopup()
document.cookie="popped=yes"
}
}
helpor_net()
//-->
</SCRIPT>