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;