Encapsulated constructor in JavaScript.

dog.js

var Dog = (function () {
  var init, create;

  /**
   * Encapsulated Constructor,
   */
  init = function (name, age) {
    this.name = name;
    this.age  = age;
  };

  /**
   * Public Constructor.
   *
   * @param  {String} name The dog's name.
   * @param  {Number} age  The dog's age.
   */
  create = function (name, age) {
    return new init(name, age);
  };

  /**
   * Instance methods.
   * These are encapsulated too.
   */
  init.prototype = {
    /**
     * Prints the dog's greeting.
     *
     * @return {void}
     */
    greet : function () {
      print("My name is " + this.name + ". " +
             "I'm " + this.age + " years old.");
    }
  };

  return {
    create : create
  };
})();

var pochi = Dog.create('Pochi', 3);
pochi.greet();
// => My name is Pochi. I'm 3 years old.