js 中的五种继承方法

正式发布的ES6中已经封装实现了其他OO语言中的继承形式，Class Extends，这里主要记录js的原型继承和借用构造函数继承

一、原型链继承

function Super(){    this.name="小明";}Super.prototype.sayName = function(){    alert(this.name)};function Sub(){}Sub.prototype = new Super();var instance = new Sub();instance.sayName();//小明

原型链继承的问题

//当超类中包含引用类型属性值时，其中一个子类的多个实例中，只要其中一个实例引用属性只发生修改一个修改，其他实例的引用类型属性值也会立即发生改变//原因是超类的属性变成子类的原型属性function Super(){this.name="小明";    this.friends = ['小红','小强'];}Super.prototype.sayName = function(){    alert(this.name)};function Sub(){}Sub.prototype = new Super();var instance1 = new Sub();var instance2 = new Sub();instance1.friends.push('张三');console.log(instance1.friends);//["小红", "小强", "张三"]console.log(instance2.friends);//["小红", "小强", "张三"]

二、借用构造函数继承

function Super(){this.name="小明";    this.friends = ['小红','小强'];}Super.prototype.sayName = function(){    alert(this.name)};function Sub(){    Super.call(this);}var instance1 = new Sub();var instance2 = new Sub();instance1.friends.push('张三');console.log(instance1.friends);//["小红", "小强", "张三"]console.log(instance2.friends);//["小红", "小强"]

借用构造函数的问题

单独使用借用构造函数，没办法继承超类中的原型属性和方法

三、组合式继承（原型继承+借用构造函数继承）

组合式继承也是实际开发中最常用的继承方式

function Super(){this.name="小明";    this.friends = ['小红','小强'];}Super.prototype.sayName = function(){    alert(this.name)};function Sub(){    Super.call(this);}Sub.prototype = new Super();var instance1 = new Sub();var instance2 = new Sub();instance1.friends.push('张三');console.log(instance1.friends);//["小红", "小强", "张三"]console.log(instance2.friends);//["小红", "小强"]instance1.sayName();//小明instance2.sayName();//小明

组合式继承的问题

//组合式继承中，超类的构造函数将被调用两次function Super(){this.name="小明";    this.friends = ['小红','小强'];}Super.prototype.sayName = function(){    alert(this.name)};function Sub(){    Super.call(this);//第二次调用}Sub.prototype = new Super();//第一次调用var instance = new Sub();

四、寄生式继承

//在主要考虑对象而不是自己定义类型和构造函数的情况下，寄生式继承是一种有用的模式，但无法做到函数的复用    function createAnother(original){    var clone = Object(original);//创建一个新对象，original的副本    clone.sayName = function(){ //对象的增强，添加额外的方法        alert('hi');    }    return clone;}var person = {    name:'小明',    friends:['小红','小强']}var person1 = createAnother(person);var person2 = createAnother(person);person1.friends.push('张三');console.log(person.friends);//["小红", "小强", "张三"]console.log(person1.friends);//["小红", "小强", "张三"]console.log(person2.friends);//["小红", "小强", "张三"]

寄生组合式继承

//寄生组合式继承解决了组合式继承调用两次超类构造函数的问题function inheritPrototype(sub,superr){var prototype = Object.create(superr.prototype);//ES5中创建对象副本的方法    prototype.constructor = superr; //弥补重写原型失去的默认constructor属性    sub.prototype = prototype;}function Super(name){    this.name = name;    this.friends = ['小红','小强'];}Super.prototype.sayName = function(){    alert(this.name);}function Sub(name){    Super.call(this,name);}inheritPrototype(Sub,Super);var person1 = new Sub('小明');var person2 = new Sub('小华');person1.friends.push('张三');console.log(person1.friends);//["小红", "小强", "张三"]console.log(person2.friends);//["小红", "小强"]console.log(person1.sayName());//小明console.log(person2.sayName());//小华