this指向问题

<!DOCTYPE html>

<html lang="en">

  <head>

    <meta charset="UTF-8" />

    <meta name="viewport" content="width=device-width, initial-scale=1.0" />

    <title>Document</title>

  </head>

  <body>

  </body>

</html>

<script>

  var name = "window";

  var p2 = { name: "p2" };

  var presonal1 = {

    name: "presonal1",

    say: function () {

      console.log(this.name);

    },

  };

  let a = presonal1.say;

  a(); // window

  presonal1.say(); // presonal1

  presonal1.say.call(p2); // p2 this指向有 presonal1 指向p2

  a.call(p2); // p2 this指向有 window 指向p2

  var presonal2 = {

    name: "presonal2",

    say: () => {

      console.log(this.name);

    },

  };

  presonal2.say(); // window  say为箭头函数 没有 this 不能指向 presonal1

  presonal2.say.call(p2); // window  say为箭头函数 没有 this 不能绑定 p2

  var presonal3 = {

    name: "presonal3",

    say: function () {

      // this 指向 presonal3

      return function () {

        // 匿名函数指向window

        console.log(this.name);

      };

    },

  };

  presonal3.say()(); // window  presonal3.say() 返回一个function函数 在window执行

  presonal3.say().call(p2); // p2  presonal3.say() 返回一个function函数 在window执行 通过call指向p2

 

  var presonal4 = {

    name: "presonal4",

    say: () =>

      function () {

        console.log(this.name);

      },

  };

  presonal4.say()(); // window  presonal4.say() 返回一个function函数 指向window执行

  presonal4.say().call(p2); // p2  presonal4.say() 返回一个function函数 指向window执行 通过call指向p2

 

  var presonal5 = {

    name: "presonal5",

    say: function () {

      return () => {

        // 箭头函数自动绑定 say() 的this

        console.log(this.name);

      };

    },

  };

 

  let a2 = presonal5.say;

  a2()(); // a2指向 window

  presonal5.say()(); // presonal5 返回箭头函数 绑定say() 函数的 this

  presonal5.say().call(p2); // presonal5 presonal5.say()返回箭头函数不能通过call改变

</script>