function Person(national,age)
        {
            this.age = age;   //实例对象，每个示例不同
            Person.national = national;    //类对象,所用实例公用
            var bb = 0;  //局部变量，外面不能访问（类似局部函数）
        }

           var p = new Person("中国", 29);
            document.writeln("age:" + p.age);
            document.writeln("object national:" + p.national);
            document.writeln("Class national:" + Person.national);
            document.writeln("local var:" + p.bb);

            var p2 = new Person("美国", 31);
            document.writeln("</br>");
            document.writeln("age:" + p2.age);
            document.writeln("object national:" + p2.national);
            document.writeln("Class national:" + Person.national);
            document.writeln("local var:" + p2.bb);

            document.writeln("</br>");
            document.writeln("Class national:" + Person.national);
            //age:29 object national:undefined Class national:中国 local var:undefined 
            //age:31 object national:undefined Class national:美国 local var:undefined 
            //Class national:美国