一.ES5构造函数与继承

小问题: new关键字做了什么?

​ new会创建对象,将构造函数中的this指向创建出来的对象,也就是这个实例

方法一.利用apply或call方法

代码演示

function User(username,password){
	this.username = username
	this.password = password
	this.login = function(){
		console.log('登录')
	}
}

function Admin(username,password){
	User.apply(this,arguments)
	this.delete = funciton(){
		console.log('删除')
	}
}

let Manage = new Admin('zhanghao','mima')

console.log(Manage)	//Admin {
  								username: 'zhanghao',
  								password: 'mima',
  								login: [Function (anonymous)],
  								delete: [Function (anonymous)]
							 }

方法二.利用prototype

代码演示

function User(username,password){
	this.username = username
	this.password = password
	this.login = function(){
		console.log('登录')
	}
}

function Admin(username,password){
	this.delete = funciton(){
		console.log('删除')
	}
}

Admin.prototype = new User() //将User实例赋值给Admin.prototype,那么Admin的实例也就可以追溯上去从而使用User的东西完成函								数的方法继承效果

let Manage = new Admin('zhanghao','mima')
console.log(Manage.username)	//undefined
Manage.login()	//登录
Manage.delete()	//删除

二. ES6类与继承

代码演示

// 生成类
class User {
	constructor(username,password){
		this.username = username
		this.password = password
	}
	login(){
		console.log(this)
		console.log('登录')
	}
}

// 继承类,并且再多添加点东西
class Admin extends User {
	delete(){
		console.log('删除')
	}	
}

let Manage = new Admin('zhanghao','mima')
Manage.login()	//Admin { username: 'zhanghao', password: 'mima' }
				  登录
Manage.delete()	//删除

tips:

​ (1).一般情况constructor中不要用return,不然会导致类下面的函数不会被暴露给实例使用