JavaScript面向对象之继承

1.      原型链继承：

function SuperType(){
this.property = true;
}

SuperType.prototype.getSuperValue = function (){
return this.property;
}

function SubType(){
this.subproperty = false;
}

SubType.prototype = new SuperType();
SubType.prototype.getSubValue = function (){
return this.subproperty;
}

var instance = new SubType();
alert(instance.getSuperValue());

alert(instance instanceof Object);
alert(instance instanceof SuperType);
alert(instance instanceof SubType);

alert(Object.prototype.isPrototypeOf(instance));
alert(SuperType.prototype.isPrototypeOf(instance));
alert(SubType.prototype.isPrototypeOf(instance));

问题1.包含引用类型值的原型。

问题2.不能像超类型的构造方法传参。

2.借用构造函数（constructor stealing）(伪造对象或经典继承)
(1)无参：

function SuperType(){
this.colors = ['red','blue','green'];
}

function SubType(){
SuperType.call(this);
}

var instance1 = new SubType();
instance1.colors.push("black");
alert(instance1.colors);

var instance2 = new SubType();
var instance3 = new SuperType();
alert(instance3.colors);

(2)传参：

function SuperType(name){
this.name = name;
}

function SubType(){
SuperType.call(this,"zhangsan");
this.age = 20;
}

var instance1 = new SubType();

alert(instance1.name);  //zhangsan
alert(instance1.age);  //20

var instance2 = new SuperType();
alert(instance2.name);  //undefined
alert(instance2.age);  //undefined

问题：方法在构造函数中定义，无法复用。

3.组合继承（combination inheritance）(伪经典继承)

function SuperType(name){
this.name = name;
this.colors = ["red","blue","green"];
}

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

function SubType(name,age){
//继承属性
SuperType.call(this,name);
this.age = age;
}

//继承方法
SubType.prototype = new SuperType();

SubType.prototype.sayAge = function(){
alert(this.age);
}

var instance1 = new SubType("zhangsan",20);
instance1.colors.push("black");

alert(instance1.colors);    // red,blue,green,black
instance1.sayName();  //zhangsan
instance1.sayAge();   // 20

var instance2 = new SubType("lisi",30);
alert(instance2.colors);  // red,blue,green
instance2.sayName();  //lisi
instance2.sayAge();  // 30

4. 原型式继承（Prototypal inheritance）

function object(o){
function F(){}
F.prototype = o;
return new F();
}

var person = {
name:"zhangsan",
friends :["guojing","huangrong"]
};

var anotherPerson = object(person);
anotherPerson.name = "lisi";
anotherPerson.friends.push("zhoubotong");

var yetAnotherPerson = object(person);
yetAnotherPerson.name = "wangwu";
yetAnotherPerson.friends.push("yidengdashi");

alert(person.friends);  //  guojing,huangrong,zhoubotong,yidengdashi

5.寄生式继承（parasitic）

function object(o){
function F(){}
F.prototype = o;
return new F();
}

function createAnother(original){
var clone = object(original);
clone.sayHi = function(){
alert("hello");
};
return clone;
}

var person = {
name:"zhangsan",
friends :["guojing","huangrong"]
};

var anotherPerson = createAnother(person);
//anotherPerson.sayHi();  //hello
anotherPerson.name = "lisi";
anotherPerson.friends.push("zhoubotong");

var yetAnotherPerson = object(person);
yetAnotherPerson.name = "wangwu";
yetAnotherPerson.friends.push("yidengdashi");

alert(person.friends);  //  guojing,huangrong,zhoubotong,yidengdashi
alert(anotherPerson.friends);  //  guojing,huangrong,zhoubotong,yidengdashi
alert(yetAnotherPerson.friends);  //  guojing,huangrong,zhoubotong,yidengdashi

6.寄生组合式继承

function object(o){
function F(){}
F.prototype = o;
return new F();
}

function inheritPrototype(subType,superType){
var prototype = object(superType.prototype);
prototype.constructor = subType;
subType.prototype = prototype;
}

function SuperType(name){
this.name = name;
this.colors = ["red","blue","green"];
}

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

function SubType(name,age){
SuperType.call(this,name);
this.age = age;
}

inheritPrototype(SubType,SuperType);

SubType.prototype.sayAge = function(){
alert(this.age);
}

var instance = new SubType("zhangsan",30);
alert(instance.name);  //zhangsan
instance.sayName();  //zhangsan
instance.sayAge();   // 30