gistfile1.js

function loadScript(url, callback) {
	var script = document.createElement('script'),
		head = document.getElementsByTagName('head')[0];
	
	// two methods for detecting when scripts have loaded
	script.onreadystatechange = function () {
		if (script.readyState == 'loaded' || script.readyState == 'complete') {
			callback();
		}
	}                            
	script.onload = callback;
	script.src = url;
	head.insertBefore(script, head.lastChild);
}