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;