let dog = {
  name: "Spot",
  numLegs: 4,
  sayLegs: function() {return "This dog has " + this.numLegs + " legs.";}
};

dog.sayLegs();

얘는 잘굴러가고

let dog = {
  name: "Spot",
  numLegs: 4,
  sayLegs: () => "This dog has " + this.numLegs + " legs."
};

dog.sayLegs();

얘는 Cannot read properties of undefined 뜨는데 왜그런거임?