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;