object creation problem

gistfile1.js

var person = Object.create(null);

// Here we are reusing the previous gettersetter functions
Object.defineProperty(person, 'name', { get: get_full_name , set: set_full_name , configurable: true, enumerable:   true });

// And adding the `greet' function
person.greet = function (person) {
    return this.name + ': Why, hello there, ' + person + '.' ;
} 

// Then we can share those behaviours with Mikhail
// By creating a new object that has it's [[Prototype]] property
// pointing to `person'.
var mikhail = Object.create(person);
mikhail.first_name = 'Mikhail';
mikhail.last_name  = 'Weiß';
mikhail.age        = 19;
mikhail.gender     = 'Male';

// And we can test whether things are actually working.
// First, `name' should be looked on `person'
    alert(mikhail.name);
// => 'Mikhail Weiß'

// Setting `name' should trigger the setter
mikhail.name = 'Michael White';

// Such that `first_name' and `last_name' now reflect the
// previously name setting.
mikhail.first_name;
// => 'Michael'var person = Object.create(null);

// Here we are reusing the previous gettersetter functions
Object.defineProperty(person, 'name', { get: get_full_name , set: set_full_name , configurable: true, enumerable:   true });

// And adding the `greet' function
person.greet = function (person) {
    return this.name + ': Why, hello there, ' + person + '.' ;
} 

// Then we can share those behaviours with Mikhail
// By creating a new object that has it's [[Prototype]] property
// pointing to `person'.
var mikhail = Object.create(person);
mikhail.first_name = 'Mikhail';
mikhail.last_name  = 'Weiß';
mikhail.age        = 19;
mikhail.gender     = 'Male';

// And we can test whether things are actually working.
// First, `name' should be looked on `person'
    alert(mikhail.name);
// => 'Mikhail Weiß'

// Setting `name' should trigger the setter
mikhail.name = 'Michael White';

// Such that `first_name' and `last_name' now reflect the
// previously name setting.
mikhail.first_name;
// => 'Michael'
mikhail.last_name;
// => 'White'

// `greet' is also inherited from `person'.
mikhail.greet('you');
// => 'Michael White: Why, hello there, you.'

// And just to be sure, we can check which properties actually
// belong to `mikhail'
 Object.keys(mikhail);
// => [ 'first_name', 'last_name', 'age', 'gender' ]

mikhail.last_name;
// => 'White'

// `greet' is also inherited from `person'.
mikhail.greet('you');
// => 'Michael White: Why, hello there, you.'

// And just to be sure, we can check which properties actually
// belong to `mikhail'
 Object.keys(mikhail);
// => [ 'first_name', 'last_name', 'age', 'gender' ]