Function to include a javascript file dynamically into a HTML page, with a callback when the script is loaded.

loader.js

function loadJS(src, cb) {
  var inc = document.createElement("script");
  inc.onload = inc.onreadystatechange = function() {
		if (cb && inc.readyState == "loaded" || inc.readyState == "complete" || inc.readyState == 4)
		  cb();
	};
	inc.src = src;
	document.getElementsByTagName("head")[0].appendChild(inc);
};