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;