Simple Javascript script file injection (via http://www.quora.com/What-are-the-use-cases-for-RequireJS-vs-Yepnope-vs-LABjs)

example.js

<script>
(function(d,s){ 
  var x = d.createElement(s),
      o = d.getElementsByTagName(s)[0];
  x.src="script.js"; // your script here
  x.async=true; // mostly optional
  o.parentNode.insertBefore(s,o); // inject
})(document,'script');
</script>