function ClassA()  {
}

ClassA.prototype.id = 1998;
ClassA.prototype.sayId =function(){
   alert(this.id);
};

functionClassB(){
}

ClassB.prototype=newClassA();
ClassB.prototype.name="";
ClassB.prototype.sayName=function(){
   alert(this.name);
}

var  obj1 = new ClassA();
var  obj2 = new ClassB();
obj1.id = 1998;
obj2.id= 2000;
obj2.name ="悉尼奥运会";
obj1.sayId();  //输出"1998"
obj2.sayId();  //输出"1998"
obj2.sayName();  //输出"悉尼奥运会"

alert(obj2instanceofClassA);  //输出"true"
alert(obj2 instanceofClassB);  //输出"true"

function ClassA(id) {
   this .id = id;
}

ClassA.prototype.sayId = function() {
   alert(this.id);
};

function ClassB(id, name) {
   ClassA.call(this, id);
  this.name =name;
}

ClassB.prototype =  new ClassA();
ClassB.prototype.sayName=function(){
   alert(this.name);
}

function ClassB(id, name) {
    //this.newMethod = ClassA;
  //this.newMethod(id);
  //delete this.newMethod;
  ClassA.call(this, id);  //this指向ClassB的对象

  this.name =name;
  this.sayName = function() {
     alert(this.name);
   };
}