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;