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;