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;