js中的this指向问题

this指向两句话口诀：

1.this永远指向函数执行的环境，而不是声明的环境

2.箭头函数的this指向父级

一、正常函数的this

function fn1(){
  console.log(this)  
}

fn1() //this===window

fn1.call({x:100}) //this==={x:100}

const fn2 = fn1.bind({x:200})

fn2() //this==={x:200}

二、对象的this和箭头函数的this

const zhangsna = {
  name:'张三',
  sayHi(){
    console.log(this)  //this是当前对象  
  }  
  wait(){
    settimeOut(function(){
      console.log(this)  //this是window
    })  
  }
}

const zhangsna = {
  name:'张三',
  sayHi(){
    console.log(this)  //this是当前对象  
  }  
  wait(){
    settimeOut(()={
      console.log(this)  //this是当前对象
    })  
  }
}

三、构造函数的this

class People {
  constructor(name){
     this.name = name
     this.age = age  
  }  
  sayHi(){
     console.log(this)  
  }
}

let person = new People('张三')
person.sayHi()  //person对象