首先看一下下面的代码
function User(name , age, career) {
this.name = name
this.age = age
this.career = career
}
const user = new User('ryan', 19, 'fe')
console.log(user) // {name: "ryan", age: 19, career: "fe"}
function newUser(name , age, career) {
return {
name,
age,
career ,
}
}
const newuser = newUser('ryan', 19, 'fe')
console.log(newuser) // {name: "ryan", age: 19, career: "fe"}
想想这两种获取对象的方式有什么不同？
再看看下面的代码
function User(name , age, career) {
this.name = name
this.age = age
this.career = career
}
User.prototype.sayName = function () {
console.log("Hello")
}
const user = new User('ryan', 19, 'fe')
console.log(user) // {name: "ryan", age: 19, career: "fe"}
user.sayName() // Hello
function newUser(name , age, career) {
return {
name,
age,
career ,
}
}
newUser.prototype.sayName = function () {
console.log("Hello")
}
const newuser = newUser('ryan', 19, 'fe')
console.log(newuser) // {name: "ryan", age: 19, career: "fe"}
newuser.sayName() // Uncaught TypeError: newuser.sayName is not a function
看到这里是不是感觉好像明白了什么
new 的过程和普通的函数返回不同，new 其实是一种继承的方式， 通过new，实例与构造函数通过原型链连接了起来出来，所以实例能访问到构造函数的属性，具体过程如下
- 开辟一个块内存，创建一个空对象
- 执行构造函数，对这个空对象进行构造
- 给这个空对象添加proto属性
__proto__ = User.prototype
