window.onload = function() { 
   if (!document.getElementsByTagName) { 
      return false; 
   } 
   // create an array of objects of each link in the document 
   var popuplinks = document.getElementsByTagName("a");   
   for (var i=0; i < popuplinks.length; i++) {    
   
      if (popuplinks[i].className == "popup") {         
         popuplinks[i].onclick = function() {    
         openPopUp(this.getAttribute("href"));    
         return false;     
         }     
      } 
   } 
} 

function openPopUp(linkURL) { 
   window.open(linkURL,'popup','width=600,height=500,scrollable=true') 
}