setInterval和setTImeout中的this指向问题

var num = 0;
function Obj (){
this.num = 1,
this.getNum = function(){
console.log(this.num);
},
this.getNumLater = function(){
setTimeout(function(){
console.log(this.num);
}, 1000)
}
}
var obj = new Obj;
obj.getNum();//1　　打印的是obj.num，值为1
obj.getNumLater()//0　　打印的是window.num，值为0

var num = 0;
function Obj (){
const that = this; //将this存为一个常量，此时的this指向obj
this.num = 1,
this.getNum = function(){
console.log(this.num);
},
this.getNumLater = function(){
setTimeout(function(){
console.log(that.num); //利用闭包访问that，that是一个指向obj的指针
}, 1000)
}
}
var obj = new Obj;
obj.getNum();//1　　打印的是obj.num，值为1
obj.getNumLater()//1　　打印的是obj.num，值为1

var num = 0;
function Obj (){
this.num = 1,
this.getNum = function(){
console.log(this.num);
},
this.getNumLater = function(){
setTimeout(function(){
console.log(this.num);
}.bind(this), 1000) //利用bind()将this绑定到这个函数上
}
}
var obj = new Obj;
obj.getNum();//1　　打印的为obj.num，值为1
obj.getNumLater()//1　　打印的为obj.num，值为1

var num = 0;
function Obj (){
this.num = 1,
this.getNum = function(){
console.log(this.num);
},
this.getNumLater = function(){
setTimeout(() => {
console.log(this.num);
}, 1000) //箭头函数中的this总是指向外层调用者，也就是Obj
}
}
var obj = new Obj;
obj.getNum();//1　　打印的是obj.num，值为1
obj.getNumLater()//1　　打印的是obj.num，值为1