(function trackOutbounds() {
  if (typeof ga == 'undefined'){
    return;
  }

  var hitCallbackHandler = function(url,win) {
      if (win) {
        window.open(url, win);
      } else {
          window.location.href = url;
        }
    };

    var addEvent = function(el, eventName, handler) {

    if (el.addEventListener) {
      el.addEventListener(eventName, handler);
      } else {
      el.attachEvent('on' + eventName, function(){
        handler.call(el);
        });
    }
  }

  if (document.getElementsByTagName) {
    var el = document.getElementsByTagName('a');
    var getDomain = document.domain.split('.').reverse()[1] + '.' + document.domain.split('.').reverse()[0];

    // Look thru each a element
    for (var i=0; i < el.length;i++) {

      // Extract it's href attribute
      var href = (typeof(el[i].getAttribute('href')) == 'string' ) ? el[i].getAttribute('href') : '';

      // Query the href for the top level domain (xxxxx.com)
      var myDomain = href.match(getDomain);

      // If link is outbound and is not to this domain
      if ((href.match(/^(https?:|\/\/)/i)  && !myDomain) || href.match(/^mailto\:/i)) {

        // Add an event to click
        addEvent(el[i],'click', function(e) {
          var url = this.getAttribute('href'), win = (typeof(this.getAttribute('target')) == 'string') ? this.getAttribute('target') : '';
          var label = (typeof(this.getAttribute('name')) == 'string') ? this.getAttribute('name') : '';

              console.log ("add event", url);
          // Log even to Analytics, once done, go to the link
          ga('send', 'event', 'outbound', url, label,
            {'hitCallback': hitCallbackHandler(url,win)},
            {'nonInteraction': 1}
          );

          e.preventDefault();
        });
      }
    }
  }
  var el = document.querySelectorAll(".toc_list a");
  for (var i=0; i < el.length;i++) {
    addEvent(el[i],'click', function(e) {
      var text = this.textContent
      ga('send', 'event', 'toc', text);
    });
  }
  var pageTop = document.getElementById('page-top');
  addEvent(pageTop,'click', function(e) {
    ga('send', 'event', 'page-top');
  });
})();