function externalLinks() { 
 if (!document.getElementsByTagName) return; 
 var anchors = document.getElementsByTagName('a'); 
 for (var i=0; i<anchors.length; i++) { 
   var anchor = anchors[i]; 
   if (anchor.getAttribute('href') && 
       anchor.getAttribute('rel') == 'ext') 
     anchor.target = '_blank'; 
 } 
} 
window.onload = externalLinks;