js 模拟类， 继承

var initializing = false, fnTest = /xyz/.test(function() { xyz; }) ? /\b_super\b/ : /.*/;
    //构造基类
    this.jaClass = function() {};
    jaClass.extend = function(props){
        var _super = this.prototype;
        initializing = true;
        var prototype = new this();
        initializing = false;

        for (var name in props){
            //这一段是赋值到prototype中，运用三元运算符的方式很灵活
            //满足函数的条件作为函数插入到prototype中
            prototype[name] = typeof props[name] =="function" &&
            typeof _super[name] == "function" && fnTest.test(props[name]) ?
                (function(name, fn) {
                    return function(){
                        var tmp = this._super;
                        this._super = _super[name];
                        var ret = fn.apply(this, arguments);
                        this._super = tmp;
                        return ret;
                    };
                })(name, props[name]) :
                props[name]
        }

        function Class(){
            if(!initializing && this.ctor)
                this.ctor.apply(this, arguments);
        }

        //子类prototype指向父类的实例，继承的关键
        Class.prototype = prototype ;
        Class.prototype.constructor = Class;
        //子类自动获得extend方法，arguments.callee 指向当前正在执行的函数
        Class.extend = arguments.callee;
        return Class;
    };