JavaScript中this面试题

关于Javascript中以下obj调用sing时输出的this指向

/*
 * @Author: Wen
 * @Url: wenlk.com
 * @Date: 2024-03-31 18:54:55
 * @LastEditTime: 2024-03-31 19:00:49
 * Copyright (c) 2024 by wenlk.com, All Rights Reserved. 
 */

const obj = {
  name: 'Billy',
  sing() {
    console.log('a',this);
    var anotherFunc = function () {
      console.log('b',this)
    }
    anotherFunc()
  }
}
// a obj
// b window

const obj1 = {
  name: 'Billy',
  sing() {
    console.log('a',this);
    var anotherFunc = ()=> {
      console.log('b',this)
    }
    anotherFunc()
  }
}
//a obj1
//b obj1

const obj2 = {
  name: 'Billy',
  sing() {
    console.log('a',this);
    var anotherFunc = function() {
      console.log('b',this)
    }
    return anotherFunc.bind(this)
  }
}
// ƒ () {
//   console.log('b',this)
// }