var cache = [];
(function($) {
    $.preLoadImages = function() {
        var args_len = arguments.length;
        for (var i = args_len; i--; ) {
            var cacheImage = document.createElement('img');
            cacheImage.src = arguments[i];
            cache.push(cacheImage);
        }
    }
    $.addImageToCache = function() {
        var cacheImage = document.createElement('img');
        cacheImage.src = arguments[0];
        cache.push(cacheImage);
    }
})(jQuery)