Are private constructor properties copied during new object creation in JavaScript?

Question

JavaScript

In this example, how is it that each object created using the User constructor has its own variables firstName, surname.

function User() {

  var firstName, surname;

  this.setFirstName = function(newFirstName) {
    firstName = newFirstName;
  };

  this.setSurname = function(newSurname) {
    surname = newSurname;
  };

  this.getFullName = function() {
    return firstName + ' ' + surname;
  }
}

var user = new User();
var user2 = new User();

user.setFirstName("Петя");
user.setSurname("Иванов");

user2.setFirstName("Петя222");
user2.setSurname("Иванов222");
alert( user.getFullName() );
alert( user2.getFullName() );

Answer 1

Nope. Each call creates new functions setFirstName , setSurname , getFullName , which receive new closure variables firstName , surname .