Change jQuery to use the more performant classList over string concatenation methods, when ClassList is available

jquery.classList.js

/**
 * jQuery extension, add support `classList`.
 *
 * @author	RubaXa	<trash@rubaxa.org>, bryanerayner <bryan@bryanerayner.ca>
 * @license	MIT
 */

(function ($) {
    var
		  _rspace = /\s+/
		, _$cache = $('<div/>')

		, _div = _$cache[0]
		, _classList = _div.classList
		, _supportsArgs
    ;


    var _each = function ($el, method, callback) {
        $el.each(function (i) {
            _$cache[0] = this;
            _$cache[method](callback.call(this, i, _$cache.attr('class')));
        });
    }

    var _factory = function (method) {
        return function (value) {
            var typeOf = typeof value, i = this.length;

            if ('string' === typeOf) {
                value = $.trim(value);

                if ("" !== value) {
                    value = value.split(_rspace);

                    var j, n = value.length, list;

                    while (i--) {
                        list = this[i].classList;

                        if (1 === n) {
                            list[method](value[0]);
                        }
                        else if (_supportsArgs) {
                            list[method].apply(list, value);
                        }
                        else {
                            for (j = 0; j < n; j++) {
                                list[method](value[j]);
                            }
                        }
                    }
                }
            }
            else if ((void 0 === value) && ('remove' === method)) {
                while (i--) {
                    this[i].className = '';
                }
            }
            else if ('function' === typeOf) {
                _each(this, method + 'Class', value);
            }

            return this;
        }
    }




    if (_classList) {
        _classList.add('-a', 'b-');
        _supportsArgs = /-a/.test(_div.className) && /b-/.test(_div.className);


        /**
		 * Has class
		 *
		 * @param {string} className
		 * @returns {boolean}
		 */
        $.fn.hasClass = function (className) {
            className = $.trim(className);
            var splitClassNames = className.split(_rspace);
            var s = splitClassNames.length;
            var i = this.length;
            var numContained = 0;

            while (i--) {
                numContained = 0;
                for (var q = 0; q < s; q++) {
                    if (this[i].classList.contains(splitClassNames[q])) {
                        numContained++;
                    }
                }
                if (numContained === s)
                {
                    return true;
                }
            }

            return false;
        };


        /**
		 * Add class
		 *
		 * @param	{string|function}  value
		 * @returns	{jQuery}
		 */
        $.fn.addClass = _factory('add');


        /**
		 * Remove class
		 *
		 * @param	{string|function}  value
		 * @returns	{jQuery}
		 */
        $.fn.removeClass = _factory('remove');
    }




    // Cleanup
    _$cache[0] = _div = _classList = null;
})(jQuery);

Revised the file to properly declare nested functions (they should be variables) and support cases where 'hasClass' is queried by user input with a space separated string