Adding script tag asynchronously

async.js

<script type="text/javascript">
(function(){
  var s = document.createElement('script');
     s.type = 'text/javascript';
     s.async = true;
     s.src = 'https://ajax.googleapis.com/ajax/libs/jquery/1.5.1/jquery.min.js';
  (document.getElementsByTagName('head')[0]||document.getElementsByTagName('body')[0]).appendChild(s);
})();
</script>