Prototype

在Constructor的章节中我们使用建立实体的方式

function Person(name, age){
    this.name = name
    this.age = age
}
let c = new Person("Dennis", 22)
console.log(c) //Person { name: 'Dennis', age: 22 }

但今天我想建立一个function可以自我介绍Constructor的方法是

function Person(name, age){
    this.name = name
    this.age = age
    this.SayHi = function() { 
        console.log(`$Hello I'm ${this.name} my age is ${this.age} `)
    }
}
let c = new Person("Dennis", 22)
c.SayHi() //$Hello I'm Dennis my age is 22 

还有一个就是今天的重点Prototype

当我们使用new建立一个物件的时候SayHi这个function会一直重复并且占用记忆体,但明明都一样何必多创造
所以我们把他抽取出来透过prototype指向SayHi这个function

function Person(name, age){
    this.name = name
    this.age = age
}

Person.prototype.SayHi = function(){
    console.log(`Hello I'm ${this.name} my age is ${this.age}`)
}

let c = new Person("Dennis", 22) 
c.SayHi() //Hello I'm Dennis my age is 22

在这里就透过prototype去指向SayHi function了

JavaScript prototype无所不在

let num = 23
let Num = new Number(23)

console.log(typeof(num)) //number
console.log(typeof(Num)) //object

上面的图完整示范了在JavaScript不论你定义number、string等等,都会透过Prototype去继承相关的method