window.__safeLoadScript = function(src, callback) {

	function addEvent(obj, type, fn) {
		if (obj.attachEvent) {
			obj['e' + type + fn] = fn;
			obj[type + fn] = function() { obj['e' + type + fn](window.event); }
			obj.attachEvent('on' + type, obj[type + fn]);
		} else
			obj.addEventListener(type, fn, false);
	}

	function async_load(src, callback) {
		var s = document.createElement('script');
		s.type = 'text/javascript';
		s.async = true;
		var protocol = (("https:" == document.location.protocol) ? "https://" : "http://");
		s.src = protocol + src;
		var x = document.getElementsByTagName('script')[0];
		x.parentNode.insertBefore(s, x);
		s.onload = s.onreadystatechange = function() {
			if(callback && (!this.readyState || this.readyState == "loaded" || this.readyState == "complete")) {
				callback();
			}
		};
	}

	addEvent(window, "load", function() { 
		async_load(src, callback);
	});
};

Safely loads a javascript file asynchronously

Example:

	(function() {
		__safeLoadScript("http://ajax.googleapis.com/ajax/libs/jquery/1.4.2/jquery.min.js", function() {
			alert(jQuery);
		});
	})();

Safe Script Load

javascript

JavaScript