Hey, nice article :) Like most of the times you need to use arrow function its when you want your scope to be preserved. Any others times just semantic sugar.

// Method functions
var Person = {
  firstName: "First",
  lastName: "Last",
  nameArrow: () => this.firstName + " " + this.lastName,
  nameNormal: function(){
    return this.firstName + " " + this.lastName;
  }
};

console.log(Person.nameArrow());  // prints 'undefined undefined'
console.log(Person.nameNormal()); // prints 'undefined undefined'

You have and mistake in here should be

console.log(Person.nameNormal()); // prints 'First Last'