Load JS on demand

loadScript.js

// Inspired (stolen?) from JQuery (https://github.com/jquery/jquery/blob/1.3.2/src/ajax.js#L264)
// and http://www.nczonline.net/blog/2009/07/28/the-best-way-to-load-external-javascript/
function loadJS(url, callback){
	var head = document.getElementsByTagName("head")[0];
	var script = document.createElement("script");
	script.src = url;
	script.async = true;
 
	// Attach handlers for all browsers
	script.onload = script.onreadystatechange = function(){
		if ( !this.readyState || this.readyState == "loaded" || this.readyState == "complete" ) {
			callback();
			
			// Handle memory leak in IE
			script.onload = script.onreadystatechange = null;
			head.removeChild( script );
		}
	};
	
	head.appendChild(script);
}