ensure.js, inspired by ensure.js on codeplex.com

ensure.js

var ensure = (function() {
	var loader = function() {};

	loader.prototype = {
		queues: { js: {}, css: {} },

		load: function(data, callback, context) {
			if (! data.css) data.css = [];
			if (! data.js) data.js = [];
			this.queueCSS(data.css, this.bind(function() {
				this.queueJS(data.js, this.bind(callback, context));
			}));
		},

		bind: function(func, context) {
			context = context || this;
			return function() { func.apply(context, arguments); }
		},

		tagExists: function(type, src) {
			var tagName = "script";
			var attName = "src";
			if (type == "css") {
				var tagName = "link";
				var attName = "href";
			}
			var tag = document.createElement(tagName);
			tag[attName] = src;
			var tags = document.getElementsByTagName(tagName);
			for (var i=0; i<tags.length; i++) {
				if (tag[attName] === tags[i][attName]) {
					return true;
				}
			}
			return false;
		},

		process: function(type, src) {
			if (this.queues[type][src]["status"] == "init") {
				this.queues[type][src]["status"] = "loading";
				this["get"+type.toUpperCase()].call(this, src);
			}
			else if (this.queues[type][src]["status"] == "loaded")
			{
				this.finish(type, src);
			}
		},

		finish: function(type, src) {
			this.queues[type][src]["status"] = "loaded";
			while(this.queues[type][src]["callbacks"].length > 0) {
				(this.queues[type][src]["callbacks"].shift())();
			}
		},

		queue: function(type, src, callback) {
			if (! this.queues[type][src]) {
				this.queues[type][src] = {};
				this.queues[type][src]["callbacks"] = [];
				if (this.tagExists(type, src)) this.queues[type][src]["status"] = "loaded";
				else this.queues[type][src]["status"] = "init";
			}
			this.queues[type][src]["callbacks"].push(callback);
			this.process(type, src);
		},

		queueCSS: function(css_list, callback) {
			var len = css_list.length;
			if (len > 1) {
				this.queue("css", css_list.shift(), this.bind(function() {
					this.queueCSS(css_list, callback);
				}, this));
			}
			else if (len == 1) {
				this.queue("css", css_list.shift(), callback);
			}
			else
			{
				callback();
			}
		},

		queueJS: function(js_list, callback) {
			var len = js_list.length;
			if (len > 1) {
				this.queue("js", js_list.shift(), this.bind(function() {
					this.queueJS(js_list, callback);
				}, this));
			}
			else if (len == 1) {
				this.queue("js", js_list.shift(), callback);
			}
			else
			{
				callback();
			}
		},

		getHead: function() {
			if (! this.head) {
				this.head = document.getElementsByTagName("head")[0] || document.documentElement;
			}
			return this.head;
		},

		getJS: function(src) {
			this.log("getJS: "+src);
			jQuery.getScript(src, this.bind(function() {
				this.finish("js", src);
			}, this));
		},

		getCSS: function(src) {
			this.log("getCSS: "+src);
			var link = document.createElement('link');
			link.setAttribute("href", src);
			link.setAttribute("rel", "Stylesheet");
			link.setAttribute("type", "text/css");
			this.getHead().appendChild(link);

			this.finish("css", src);
		},

		log: function(msg) {
			
		}
	};

	var l = new loader();
	return function(data, callback, context) {
		return l.load(data, callback, context);
	};
})();