js中 this的指向，如果工作

<script>
  function fun() {
    console.log(this)
  }

  fun() // Window

  let obj = {
    a:fun
  }

  obj.a() // obj

  function test2(c) {
    c&&c()
  }
  test2(obj.a) // Window
  // 怎么改变为指向obj?
  test2(obj.a.call(obj)) // obj
  test2(obj.a.bind(obj)) // obj
  test2(obj.a.apply(obj)) // obj
</script>

<script>
  class Test {
    fun = () => {
      console.log(this);
    };

    fun1() {
      console.log(this);
    }
  }

  let test = new Test();
  test.fun(); // Test
  console.log(this) // Window
  test.fun.call(this);  // Test  为啥不是win,原因箭头函数没有this，剪头函数的this是继承父执行上下文里面的this ，

  test.fun1()  // Test

  test.fun1.call(this) // Window
</script>

<script>
  var person = {
    fullName: function() {
      return this.firstName + " " + this.lastName;
    }
  }
  var person1 = {
    firstName:"John",
    lastName: "Doe",
  }
  var person2 = {
    firstName:"Mary",
    lastName: "Doe",
  }
  console.log(person.fullName.call(person2))  // 将返回 "Mary Doe"
</script>

<script>
  var x = 11;
  var obb = {
    x: 222,
    y: {
      x:333,
      obc: function f() {
        console.log(this)
        var x = 111;
        var obj = {
          x: 22,
          say: () => {
            console.log(this.x);
          }
        }
        obj.say()
      }
    }
  }
  obb.y.obc() // 333
</script>

js箭头函数的this指向：

https://blog.csdn.net/weixin_42519137/article/details/88053339

全面的JS this指向问题 以及如何改变this 指向的方法(call、apply、bind区别)适合初学者的一篇文章

https://blog.csdn.net/weixin_42207353/article/details/104909252