javascript関数における例示的なオブジェクト、クラスオブジェクト、ローカル変数(局所関数)

 function Person(national,age)
        {
            this.age = age;   //    ，      
            Person.national = national;    //   ,      
            var bb = 0;  //    ，      （      ）
        }

           var p = new Person("  ", 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("  ", 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:   local var:undefined 
            //age:31 object national:undefined Class national:   local var:undefined 
            //Class national: