How some different companies load their third-party JS async style

async.html

<!-- Google Analytics -->
<script type="text/javascript">
  var _gaq = _gaq || [];
  _gaq.push(['_setAccount', 'UA-XXXXX-X']);
  _gaq.push(['_trackPageview']);

  (function() {
    var ga = document.createElement('script'); ga.type = 'text/javascript'; ga.async = true;
    ga.src = ('https:' == document.location.protocol ? 'https://ssl' : 'http://www') + '.google-analytics.com/ga.js';
    var s = document.getElementsByTagName('script')[0]; s.parentNode.insertBefore(ga, s);
  })();
</script>

<!-- Optimized version: http://mathiasbynens.be/notes/async-analytics-snippet -->
<script>
  var _gaq = [['_setAccount', 'UA-XXXXX-X'], ['_trackPageview']];
  (function(d, t) {
    var g = d.createElement(t),
        s = d.getElementsByTagName(t)[0];
    g.src = '//www.google-analytics.com/ga.js';
    s.parentNode.insertBefore(g, s);
  }(document, 'script'));
</script>


<!-- BuySellAds -->
<script type="text/javascript">
(function(){
  var bsa = document.createElement('script');
     bsa.type = 'text/javascript';
     bsa.async = true;
     bsa.src = '//s3.buysellads.com/ac/bsa.js';
  (document.getElementsByTagName('head')[0]||document.getElementsByTagName('body')[0]).appendChild(bsa);
})();
</script>



<!-- Typekit -->
<script type="text/javascript">
  TypekitConfig = {
    kitId: 'abc1def',
    scriptTimeout: 3000
  };
  (function() {
    var h = document.getElementsByTagName('html')[0];
    h.className += ' wf-loading';
    var t = setTimeout(function() {
      h.className = h.className.replace(/(\s|^)wf-loading(\s|$)/g, '');
      h.className += ' wf-inactive';
    }, TypekitConfig.scriptTimeout);
    var tk = document.createElement('script');
    tk.src = '//use.typekit.com/' + TypekitConfig.kitId + '.js';
    tk.type = 'text/javascript';
    tk.async = 'true';
    tk.onload = tk.onreadystatechange = function() {
      var rs = this.readyState;
      if (rs && rs != 'complete' && rs != 'loaded') return;
      clearTimeout(t);
      try { Typekit.load(TypekitConfig); } catch (e) {}
    };
    var s = document.getElementsByTagName('script')[0];
    s.parentNode.insertBefore(tk, s);
  })();
</script>


<!-- The Deck... is this async? Just document.writing ? -->
<script type="text/javascript">
//<![CDATA[
(function(id) {
 document.write('<script type="text/javascript" src="' +
   'http://connect.decknetwork.net/deck' + id + '_js.php?' +
   (new Date().getTime()) + '"></' + 'script>');
})("DF");
//]]>
</script>


<!-- Facebook -->
<div id="fb-root"></div>
<script>(function(d, s, id) {
  var js, fjs = d.getElementsByTagName(s)[0];
  if (d.getElementById(id)) return;
  js = d.createElement(s); js.id = id;
  js.src = "//connect.facebook.net/en_US/all.js#xfbml=1&appId=200103733347528";
  fjs.parentNode.insertBefore(js, fjs);
}(document, 'script', 'facebook-jssdk'));</script>


<!-- Twitter -->
<a href="https://twitter.com/share" class="twitter-share-button">Tweet</a>
<script>!function(d,s,id){var js,fjs=d.getElementsByTagName(s)[0];if(!d.getElementById(id)){js=d.createElement(s);js.id=id;js.src="//platform.twitter.com/widgets.js";fjs.parentNode.insertBefore(js,fjs);}}(document,"script","twitter-wjs");</script>


<!-- Google Plus -->
<!-- Place this tag where you want the +1 button to render -->
<g:plusone annotation="inline"></g:plusone>

<!-- Place this render call where appropriate -->
<script type="text/javascript">
  (function() {
    var po = document.createElement('script'); po.type = 'text/javascript'; po.async = true;
    po.src = 'https://apis.google.com/js/plusone.js';
    var s = document.getElementsByTagName('script')[0]; s.parentNode.insertBefore(po, s);
  })();
</script>

Have you seen this: https://gist.github.com/1025811