js实现继承的几种方式

renyi3byi1h 8年前

 

前言:大多OO语言都支持两种继承方式: 接口继承和实现继承 ,而ECMAScript中无法实现接口继承,ECMAScript只支持实现继承,而且其实现继承主要是依靠 原型链 来实现。

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:

  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);  }

来自: https://segmentfault.com/a/1190000004730936