标签：上市 代码 组合继承 str def 多个实例 class 现在 12px
现有一个父类：
function People(name){
//属性
this.name = name
//实例方法
this.sleep=function(){
console.log(this.name + ‘正在睡觉‘)
}
}
//原型方法
People.prototype.eat = function(food){
console.log(this.name + ‘正在吃：‘ + food);
}
我们现在要构造一个子类woman，woman需要拥有people的属性和方法
function People(name){
//属性
this.name = name || Annie
//实例方法
this.sleep=function(){
console.log(this.name + ‘正在睡觉‘)
}
}
//原型方法
People.prototype.eat = function(food){
console.log(this.name + ‘正在吃：‘ + food);
}
function Woman(){
}
Woman.prototype= new People(‘haha‘);
let womanObj = new Woman();
womanObj.sleep() //haha正在睡觉
womanObj.eat(‘xiangjiao‘) //haha正在吃：xiangjiao
缺点：womanObj中的name是唯一的，因为Woman.prototype= new People(‘haha‘)，Woman继承时以及传入了name，因此按需构造多个实例。
function Woman(name){
//继承了People
People.call(this,name);
}
let womanObj = new Woman(‘haha‘);
womanObj.sleep() //haha正在睡觉
womanObj.eat(‘xiangjiao‘) // Uncaught TypeError: womanObj.eat is not a function
优点：解决了无法构造多个实例的缺点，同时父类可以有多个，只需要在Women中使用call就可以了，例如增加多一个父类People2.call();
缺点：但同时也带来了问题：无法继承父类中原型链上的方法，例如本例中womanObj中调用eat导致报错。
function Woman(name){
let instance = new People();
instance.name = name
return instance;
}
let womanObj = new Woman(‘haha‘);
console.log(womanObj instanceof People) //true
console.log(womanObj instanceof Woman) //false
womanObj.sleep() //haha正在睡觉
womanObj.eat(‘xiangjiao‘) //haha正在吃：xiangjiao
解决了原型链的继承的问题，但实际上womanObj是people的实例，而不是woman的实例了，有点借壳上市的感觉。
function Woman(name){
People.call(this,name)
}
Woman.prototype = People.prototype;
let womanObj = new Woman(‘haha‘);
Woman.prototype.constructor = Woman; //为了让constructor从people指向women
console.log(womanObj instanceof Woman) //true
console.log(womanObj instanceof People) //true
womanObj.sleep() //haha正在睡觉
womanObj.eat(‘xiangjiao‘) //haha正在吃：xiangjiao
效果其实和实例继承差不多。缺点是调用了两次父类，同时在Women.prototype上写东西会污染People.prototype
例如：
Woman.prototype.food = ‘pingguo‘
console.log(People.prototype.food) // pingguo
想不污染people.prototype其实改动一行就可以了：
Woman.prototype = Object.create(People.prototype)
这其实和下面讲到的寄生组合继承思想是相类似的。
function Woman(name){
//继承父类属性
People.call(this,name)
}
//继承父类方法
(function(){
// 创建空类
let Super = function(){};
Super.prototype = People.prototype;
//父类的实例作为子类的原型
Woman.prototype = new Super();
})();
//修复构造函数指向问题
Woman.prototype.constructor = Woman;
Woman.prototype.food = ‘pingguo‘
console.log(People.prototype.food) //undefined
let womanObj = new Woman(‘haha‘);
console.log(womanObj instanceof Woman) //true
console.log(womanObj instanceof People) //true
womanObj.sleep() //haha正在睡觉
womanObj.eat(‘xiangjiao‘) //haha正在吃：xiangjiao
所谓寄生，就是把Woman.prototype寄生在了super对象上，这样Women.prototype上的属性和方法就不会污染到People.prototype
class People{
constructor(name=‘wang‘){
this.name = name;
}
eat(){
console.log(`${this.name} eat food`)
}
}
class Woman extends People{
}
let womanObj=new Woman(‘xiaoxiami‘);
womanObj.eat() //xiaoxiami eat food
优点：代码简单，没有原型链等概念，继承效果好。
标签：上市 代码 组合继承 str def 多个实例 class 现在 12px
原文地址：https://www.cnblogs.com/AwenJS/p/12698617.html
