For the Medium article on Object.defineProperty

person.js

var Person = function Person(firstName, lastName) {
  this.firstName = firstName;
  this.lastName = lastName;

  Object.defineProperty(this, 'fullName', {
    get: function get() {
      return this.firstName + ' ' + this.lastName;
    }
  });
};

var person = new Person('David', 'White');
console.log(person.fullName); // David White