var targetBlank = {
  
    setListener: function() {
      var links = document.getElementsByTagName("a");
      for (var i = 0; i < links.length; i++) {    
        var rel = links[i].getAttribute("rel");
        if (rel=='external') {    
          var blank = document.createAttribute("target");
          blank.nodeValue = "_blank";
          links[i].setAttributeNode(blank);
        }  
      }
    },
  
    init: function() {
      this.setListener();
    },

    addEvent: function(obj, type, fn) {
      if (obj.addEventListener)
        obj.addEventListener(type, fn, false);
      else if (obj.attachEvent) {
        obj["e"+type+fn] = fn;
        obj[type+fn] = function() {obj["e"+type+fn]( window.event );}
        obj.attachEvent("on"+type, obj[type+fn]);
      }
    }    
  };


targetBlank.addEvent(window, 'load', function(){
  targetBlank.init();
});