ReferenceError: "twttr is not defined" even while using twttr.ready()

Question

Firebug console throws an error. It states that the code which I'm trying to use for tracking social events is used before //platform.twitter.com/widgets.js has finished loading asynchronously.

ReferenceError: twttr is not defined twttr.ready(function (twttr) {

However, I followed Twitter documentation ( https://dev.twitter.com/web/javascript/events ), and wrapped it around twttr.ready(), in the same way one does with Facebook events.

  <script type="text/javascript">   //load social sharing buttons async
    (function(w, d, s) {
      function go(){
        var js, fjs = d.getElementsByTagName(s)[0], load = function(url, id) {
          if (d.getElementById(id)) {return;}
          js = d.createElement(s); js.src = url; js.id = id;
          fjs.parentNode.insertBefore(js, fjs);
        };
        load('//connect.facebook.net/en_US/all.js#appId=1111111111111111&xfbml=1', 'fbjssdk');
        load('https://apis.google.com/js/plusone.js', 'gplus1js');
        load('//platform.twitter.com/widgets.js', 'tweetjs');
      }
      if (w.addEventListener) { w.addEventListener("load", go, false); }
      else if (w.attachEvent) { w.attachEvent("onload",go); }
    }(window, document, 'script'));
</script>  

<script type="text/javascript">
        window.fbAsyncInit = function() {
              FB.Event.subscribe('edge.create', function(targetUrl) {
              ga('send', 'social', 'facebook', 'like', targetUrl);
            });
              FB.Event.subscribe('edge.remove', function(targetUrl) {
              ga('send', 'social', 'facebook', 'unlike', targetUrl);
            });
        }
        twttr.ready(function (twttr) {
         twttr.events.bind('tweet', function(e){
          if(!e) return;
          ga('send', 'social', 'twitter', 'tweet', theURL);
         })
        });
    </script>

Any hints?