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 = function() {
   externalLinks();  
}