Javascript 类属性表现为共享变量

我有以下声明可以在Javascript中轻松创建类。该类来自本文： http://ejohn.org/blog/simple-javascript-inheritance/

JSfiddle： http://jsfiddle.net/xUCQp/

对象的选项似乎通过对象共享，但我需要它们作为实例变量。代码有什么问题？

法典：

/* Simple JavaScript Inheritance
 * By John Resig http://ejohn.org/
 * MIT Licensed.
 */
// Inspired by base2 and Prototype
(function() {
    var initializing = false, fnTest = /xyz/.test(function() {
        xyz;
    }) ? /'b_super'b/ : /.*/;
    // The base Class implementation (does nothing)
    this.NClass = function() {
    };
    // Create a new Class that inherits from this class
    NClass.extend = function(prop) {
        var _super = this.prototype;
        // Instantiate a base class (but only create the instance,
        // don't run the init constructor)
        initializing = true;
        var prototype = new this();
        initializing = false;
        // Copy the properties over onto the new prototype
        for (var name in prop) {
            // Check if we're overwriting an existing function
            prototype[name] = typeof prop[name] == "function" &&
                    typeof _super[name] == "function" && fnTest.test(prop[name]) ?
                    (function(name, fn) {
                        return function() {
                            var tmp = this._super;
                            // Add a new ._super() method that is the same method
                            // but on the super-class
                            this._super = _super[name];
                            // The method only need to be bound temporarily, so we
                            // remove it when we're done executing
                            var ret = fn.apply(this, arguments);
                            this._super = tmp;
                            return ret;
                        };
                    })(name, prop[name]) :
                    prop[name];
        }
        // The dummy class constructor
        function NClass() {
            var $this = this;
            // All construction is actually done in the init method
            if (!initializing && this.init)
                this.init.apply(this, arguments);
        }
        // Populate our constructed prototype object
        NClass.prototype = prototype;
        // Enforce the constructor to be what we expect
        NClass.prototype.constructor = NClass;
        // And make this class extendable
        NClass.extend = arguments.callee;
        return NClass;
    };
})();
(function (scope, undefined) {
scope.ssTypeBase = NClass.extend({
        options: {
            test: 0
        },
    init: function(test){
         this.options.test = test;   
    }
});
    var a = new scope.ssTypeBase(1);
    var b = new scope.ssTypeBase(2);
    console.log(a.options.test,b.options.test);
})(window);