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")) {
      anchor.target = anchor.getAttribute("rel"); 
    }
  } 
} 
window.onload = externalLinks;