function Base() {
  if (!(this instanceof Base)) {
    return new Base();
  }
}

function Base() {
  if (!(this instanceof Base)) {
    return new Base();
  }

  //开始成员变量定义
  this.className = "Base";
}

Base.prototype.printClassName = function(){
   console.log(this.className);
}

var base = Base(); //不使用new操作符，直接进行函数调用，自动调用new操作符
console.log(base.className);
base.printClassName();

var inherits = function(ctor, superCtor) {
  //严格相等测试:undefined/null
  //子类构造函数必须存在
  if (ctor === undefined || ctor === null)
    throw new TypeError('The constructor to "inherits" must not be ' +
      'null or undefined');
  //严格相等测试:undefined/null
  //父类构造函数必须存在
  if (superCtor === undefined || superCtor === null)
    throw new TypeError('The super constructor to "inherits" must not ' +
      'be null or undefined');

  //要点: 如果要继承的话，父类必须要有prototype对象
  //这也是为什么将所有成员方法都定义在prototype对象中！！！
  if (superCtor.prototype === undefined)
    throw new TypeError('The super constructor to "inherits" must ' +
      'have a prototype');

  //让子类构造函数对象增加一个super_指针，指向父类，这样就形成继承链
  ctor.super_ = superCtor;

  //调用Object.setPrototypeOf(子类的prototype,父类的prototype)
  Object.setPrototypeOf(ctor.prototype, superCtor.prototype);
};

// 仅适用于Chrome和FireFox，在IE中不工作：
Object.setPrototypeOf = Object.setPrototypeOf || function (obj, proto) {
 obj.__proto__ = proto;
 return obj; 
}

function Child() {
  //老样子，套路1
  if (!(this instanceof Child)) {
    return new Child();
  }
}

//注意，inherits调用不在构造函数，也不在原型对象，而是全局调用
inherits(Child, Base);

function Child() {
  //老样子，套路1
  if (!(this instanceof Child)) {
    return new Child();
  }

  //增加这句话，在调用printClassName就能正常的输出Base字符串
  Base.call(this);

  //如果要更新基类的成员变量，请在Base.call(this)之后！
  this._className = "Child"; //调用printClassName就能正常的输出Child字符串
}