Encapsulated array walking

Encapsulated array walking

    function Set (/* varargs */) {
        var i = 0,
            items = [].slice.call(arguments, 0);

        this.item = function (idx) {
            var item = items[i];
            if (idx != null) {
                if (idx in items) {
                    i = idx;
                }
                item = items[idx];
            }
            return item;
        };

        this.next = function (wrap) {
            var len = items.length;
            i = i >= len && wrap ? 0 : i + 1;
            return i < len;
        }; 

        this.prev = function (wrap) {
            i = (wrap && i <= 0 ? items.length : i) - 1;
            return i >= 0;
        };
    }