var Preloader = {
    load: function() {
        var args = $A(arguments);
        var callback = Object.isFunction(args.last()) ? args.pop() : Prototype.emptyFunction;
        var urls = Object.isArray(args[0]) ? $A(args[0]) : args;
        var loaded = 0;
        var images = $A();

        var onload = function() {
            if (++loaded == urls.length) {
                callback();

                // cleanup
                images.each(function(i) { delete i });
                images = callback = urls = null;
            }
        };

        urls.each(function(url) {
            var image = new Image();
            image.onload = image.onerror = onload;
            image.src = url;
            images.push(image);
        });
    }
};