function openPopup() {
 var url = this.href;
 window.open(url, "popup_id", "noscrollbars,resizable,width=535,height=455");
 return false;
}
function init() {
 var popups = getElementsByClassName("popup");
 for(var i=0;i<popups.length;i++) {
  popups[i].onclick=openPopup;
 }
}
window.onload=init;