window.onload = function() {
// check to see that the browser supports the getElementsByTagName method
// if not, exit the loop
if (!document.getElementsByTagName) {
return false;
}
// create an array of objects of each link in the document
var popuplinks = document.getElementsByTagName("a");
// loop through each of these links (anchor tags)
for (var i=0; i < popuplinks.length; i++) {
// if the link has a class of "popup"...
if (popuplinks[i].className == "popup") {
// add an onclick event on the fly to pass the href attribute
// of the link to our second function, openPopUp
popuplinks[i].onclick = function() {
openPopUp(this.getAttribute("href"));
return false;
}
}
}
}

function openPopUp(linkURL) {
window.open(linkURL,'popup','width=800,height=600' )
}