Object es5

gistfile1.js

var person = {};
 
Object.defineProperty(person, 'firstName', {
  get: function() { return firstName; },
  set: function(newName) { firstName = newName; },
  enumerable: true
});
 
Object.defineProperty(person, 'lastName', {
  get: function() { return lastName; },
  set: function(newName) { lastName = newName; },
  enumerable: true
});
 
Object.defineProperty(person, 'fullName', {
  get: function() { return firstName + " " + lastName },
  set: function(fullName) {
    firstName = fullName.split(" ")[0];
    lastName = fullName.split(" ")[1];
  }
});
 
person.fullName = "Jack Franklin";
console.log(person.firstName);
console.log(person.lastName);