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") == "external")   
       anchor.target = "_blank";   
   }   
}   

window.onload = externalLinks;