摘要：以下內容均基于本人對高級程序設計第三版小節的理解先看一下父類私有受保護成員，只允許在父類的構造函數中賦值公有成員引用類型的成員構造函數中的方法，打印一些基本信息原型中的方法，將構造函數中的非函數成員以格式打印方式一原型鏈繼承實現方式子類的原

以下內容均基于本人對《JavaScript高級程序設計》第三版6.3小節的理解

function Animal(name) {
    var name = name;             //"私有（受保護）"成員，只允許在父類的構造函數中賦值
    this.food = undefined;       //"公有"成員

    //引用類型的成員
    this.birthday = {            
      year: undefined
    };

    //構造函數中的方法，打印一些基本信息
    this.greeting = function() {
      console.log("Hi, my name is {" + name + "} I like eat {" + this.food + "} and my birth year is {" + this.birthday.year + "}");
    };

    //原型中的方法，將構造函數中的非函數成員以JSON格式打印
    Animal.prototype.briefInfo = function() {
      var brief = {
        name: name,
        food: this.food,
        birthday: this.birthday
      };
      console.log(JSON.stringify(brief));
    };
  }

實現方式：子類的原型指向父類的實例

子類：

function Dog() {}
Dog.prototype = new Animal();        //原型指向父類的實例

測試：

var dog1 = new Dog();
dog1.food = "shit";
dog1.birthday.year = 2015;

var dog2 = new Dog();
dog2.food = "bones";
dog2.birthday.year = 2016;

dog1.greeting();  //console: Hi, my name is {undefined} I like eat {shit} and my birth year is {2016}
dog2.greeting();  //console: Hi, my name is {undefined} I like eat {bones} and my birth year is {2016}

dog1.briefInfo();  //console: {"food":"shit","birthday":{"year":2016}}
dog2.briefInfo();  //console: {"food":"bones","birthday":{"year":2016}}

//以上，
//birthday是引用類型的屬性，所以dog1的birthday.year被dog2覆蓋了;
//無法給dog1和dog2的name賦值

存在的問題：

引用類型的對象會被子類的所有實例共享(1.1)

無法在創建子類的實例時，給父類的構造函數傳遞參數(1.2)

實現方式：在子類的構造函數中利用call(或者apply)方法執行父類構造函數(問題1.2解決)，將執行對象設為子類的this,相當于把父類構造函數中的成員拷貝了一份到子類(問題1.1解決)

子類

function Dog(name) {
  Animal.call(this, name);
}

測試

var dog1 = new Dog("tom");
dog1.food = "shit";
dog1.birthday.year = 2015;

var dog2 = new Dog("mike");
dog2.food = "bones";
dog2.birthday.year = 2016;

dog1.greeting();  //console: Hi, my name is {tom} I like eat {shit} and my birth year is {2015}
dog2.greeting();  //console: Hi, my name is {mike} I like eat {bones} and my birth year is {2016}

//briefInfo是父類原型中的屬性，并沒有被繼承，以下語句會報錯
dog1.briefInfo();  //error: dog1.briefInfo is not a function
dog2.briefInfo();  //error: dog2.briefInfo is not a function 

存在的問題：

父類原型中定義的屬性無法被繼承

綜合方式一方式二，一種很明顯的方式呼之欲出了：

實現方式：結合原型鏈繼承和經典繼承

子類

function Dog(name) {
  Animal.call(this, name);    //經典繼承
}
Dog.prototype = new Animal();    //原型鏈繼承

測試

var dog1 = new Dog("tom");
dog1.food = "shit";
dog1.birthday.year = 2015;

var dog2 = new Dog("mike");
dog2.food = "bones";
dog2.birthday.year = 2016;

dog1.greeting();  //console: Hi, my name is {tom} I like eat {shit} and my birth year is {2015}
dog2.greeting();  //console: Hi, my name is {mike} I like eat {bones} and my birth year is {2016}
dog1.briefInfo();  //console: {"name":"tom","food":"shit","birthday":{"year":2015}}
dog2.briefInfo();  //console: {"name":"mike","food":"bones","birthday":{"year":2016}}

//終于得到了預期的結果，算是較好的實現了繼承。
//但是，并不完美

存在的問題

父類的構造函數被調用了兩次

為了引出下一個繼承方式，先將函數的繼承放在一邊，看一下js中對象的繼承

(摘抄原文)
1. 原型式繼承
var person = {
  name: "martin"
  firend: ["bob", "steven"]
};
  
function object(o) {
  function F() {};
  F.prototype = o;
  return new F();
}
var anotherPerson = object(person);    //antherPerson繼承了person
2. 寄生式繼承
function createAnother(original) {
  var clone = object(original);    //原型式繼承定義的方法
  //擴展對象
  clone.sayHi = function() {
    console.log("hi");
  }
  return clone;
}

回到正題，接下來介紹一顆 “銀彈”

實現方式：

利用經典繼承拷貝父類構造中的屬性到子類

利用原型式繼承創建一個繼承父類原型的對象

將該對象的constructor屬性指向子類的構造函數(寄生式繼承:擴展對象)

將子類的prototype指向該對象

子類

function Dog(name) {
  Animal.call(this, name);
}

function F() {}
var supProto = Animal.prototype;
F.prototype = supProto;
var subProto = new F();
subProto.constructor = Dog;
Dog.prototype = subProto;

測試

var dog1 = new Dog("tom");
dog1.food = "shit";
dog1.birthday.year = 2015;

var dog2 = new Dog("mike");
dog2.food = "bones";
dog2.birthday.year = 2016;

dog1.greeting();   //console: Hi, my name is {tom} I like eat {shit} and my birth year is {2015}
dog2.greeting();   //console: Hi, my name is {mike} I like eat {bones} and my birth year is {2016}
dog1.briefInfo();  //console: {"name":"tom","food":"shit","birthday":{"year":2015}}
dog2.briefInfo();  //console: {"name":"mike","food":"bones","birthday":{"year":2016}}