question 3

[aizuyan]

Frankly, i think 【the this keyword refers to its definition surrounding scope】 is more suitable than 【the this keyword refers to its current surrounding scope】

for example:

shape.perimeter.call(shape) still return NaN，but its current surrounding scope this point shape.

[A1rPun]

Good issue :+1:

Yes you can bind, call or apply context to functions but I think adding definition will complicate the context of this question. Later in that question, surrounding scope is written without current so maybe it can be removed?

[lydiahallie]

Do you mean its definition's surrounding scope?

[aizuyan]

Yes

[aizuyan]

use babel to translate, such as :

const shape = {
  radius: 10,
  diameter() {
    return this.radius * 2;
  },
  perimeter: () => 2 * Math.PI * this.radius
};

TO

"use strict";

var _this = void 0;

var shape = {
  radius: 10,
  diameter: function diameter() {
    return this.radius * 2;
  },
  perimeter: function perimeter() {
    return 2 * Math.PI * _this.radius;
  }
};

We can see that arrow function's this point to it's definition's surrounding scope.

[shuofenghao]

Maybe I prefer to use this way. class shape { radius = 10; perimeter = () => 2 * Math.PI * this.radius; } const newShape = new shape; console.log(newShape.perimeter());

[aizuyan]

@shuofenghao

class shape {
radius = 10;
perimeter = () => 2 * Math.PI * this.radius;
}
const newShape = new shape;
console.log(newShape.perimeter());

a = newShape.perimeter
a()

Above example also work, but not correct for normal function.