function externalLinks() {

  if (!document.getElementsByTagName) {
  
    return; 
    
  } else {
  
    var anchors = document.getElementsByTagName("a");
    for (var i=0; i<anchors.length; i++) {
      var anchor = anchors[i]; 
      var relvalue = anchor.getAttribute("rel");

      if (anchor.getAttribute("href")) { 
        var external = /external/;
        var relvalue = anchor.getAttribute("rel");
        if (external.test(relvalue)) { 
          anchor.target = "_blank"; 
        }
      }
    }
  }
} 
window.onload = externalLinks;