function Person(national,age)
    {
      this.age = age;  //實例對象，每個示例不同
      Person.national = national;  //類對象,所用實例公用
      var bb = 0; //局部變量，外面不能訪問（類似局部函數）
    }

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