ES6 箭头函数this指向问题

var name = "window";
var person1 = {
    name: "person1",
    show1: function() {
        console.log(this.name);
    },
    show2: () => console.log(this.name),
    show3: function() {
        return function() {
            console.log(this.name);
        }
    },
    show4: function() {
        return () => console.log(this.name);
    }
};
var person2 = { name: "person2" };

person1.show1();  //person1
person1.show1.call(person2) //person2
person1.show2();//window
person1.show2.call(person2); //window
person1.show3()(); //window
person1.show3().call(person2);//person2
person1.show3.call(person2)();//window
person1.show4()();//person1
person1.show4().call(person2); //person1
person1.show4.call(person2)(); //person2

 以上实例说明es6箭头函数this指向所遵循的三条原则：

1. this指向函数上一层函数this，若无上一层函数，指向全局window;
2. 定义函数时所在上下文中的this；
3. this指向定义时所在的对象，而非使用时所在的对象。