JS继承的6种方法

1.原型链

基本思想：利用原型让一个引用类型继承另外一个引用类型的属性和方法。

构造函数，原型，实例之间的关系：每个构造函数都有一个原型对象，原型对象包含一个指向构造函数的指针，而实例都包含一个指向原型对象的内部指针。

原型链实现继承例子：

 function SuperType() {
 this.property = true;
 }
 SuperType.prototype.getSuperValue = function() {
 return this.property;
 }
 function subType() {
 this.property = false;
 }
 //继承了SuperType
 SubType.prototype = new SuperType();
 SubType.prototype.getSubValue = function (){
 return this.property;
 }
 var instance = new SubType();
 console.log(instance.getSuperValue());//true

2.借用构造函数

基本思想：在子类型构造函数的内部调用超类构造函数，通过使用call()和apply()方法可以在新创建的对象上执行构造函数。

例子：

 11
 function SuperType() {
 this.colors = ["red","blue","green"];
 }
 function SubType() {
 SuperType.call(this);//继承了SuperType
 }
 var instance1 = new SubType();
 instance1.colors.push("black");
 console.log(instance1.colors);//"red","blue","green","black"
 var instance2 = new SubType();
 console.log(instance2.colors);//"red","blue","green"

3.组合继承

基本思想：将原型链和借用构造函数的技术组合在一块，从而发挥两者之长的一种继承模式。

例子：

 function SuperType(name) {
 this.name = name;
 this.colors = ["red","blue","green"];
 }
 SuperType.prototype.sayName = function() {
 console.log(this.name);
 }
 function SubType(name, age) {
 SuperType.call(this,name);//继承属性
 this.age = age;
 }
 //继承方法
 SubType.prototype = new SuperType();
 Subtype.prototype.constructor = Subtype;
 Subtype.prototype.sayAge = function() {
 console.log(this.age);
 }
 var instance1 = new SubType("EvanChen",18);
 instance1.colors.push("black");
 consol.log(instance1.colors);//"red","blue","green","black"
 instance1.sayName();//"EvanChen"
 instance1.sayAge();//18
 var instance2 = new SubType("EvanChen666",20);
 console.log(instance2.colors);//"red","blue","green"
 instance2.sayName();//"EvanChen666"
 instance2.sayAge();//20

4.原型式继承

基本想法：借助原型可以基于已有的对象创建新对象，同时还不必须因此创建自定义的类型。

原型式继承的思想可用以下函数来说明：

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

例子：

 var person = {
 name:"EvanChen",
 friends:["Shelby","Court","Van"];
 };
 var anotherPerson = object(person);
 anotherPerson.name = "Greg";
 anotherPerson.friends.push("Rob");
 var yetAnotherPerson = object(person);
 yetAnotherPerson.name = "Linda";
 yetAnotherPerson.friends.push("Barbie");
 console.log(person.friends);//"Shelby","Court","Van","Rob","Barbie"

ECMAScript5通过新增Object.create()方法规范化了原型式继承，这个方法接收两个参数：一个用作新对象原型的对象和一个作为新对象定义额外属性的对象。

 var person = {
 name:"EvanChen",
 friends:["Shelby","Court","Van"];
 };
 var anotherPerson = Object.create(person);
 anotherPerson.name = "Greg";
 anotherPerson.friends.push("Rob");
 var yetAnotherPerson = Object.create(person);
 yetAnotherPerson.name = "Linda";
 yetAnotherPerson.friends.push("Barbie");
 console.log(person.friends);//"Shelby","Court","Van","Rob","Barbie"

5.寄生式继承

基本思想：创建一个仅用于封装继承过程的函数，该函数在内部以某种方式来增强对象，最后再像真正是它做了所有工作一样返回对象。

例子：

 function createAnother(original) {
 var clone = object(original);
 clone.sayHi = function () {
 alert("hi");
 };
 return clone;
 }
 var person = {
 name:"EvanChen",
 friends:["Shelby","Court","Van"];
 };
 var anotherPerson = createAnother(person);
 anotherPerson.sayHi();///"hi"

6.寄生组合式继承

基本思想：通过借用函数来继承属性，通过原型链的混成形式来继承方法

其基本模型如下所示：

function inheritProperty(subType, superType) {
var prototype = object(superType.prototype);//创建对象
prototype.constructor = subType;//增强对象
subType.prototype = prototype;//指定对象
}

例子：

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