JavaScript pseudo private function

fiddle.css

body {
  font-family: "Helvetica Neue", "Arial";
}

fiddle.html

<h1>Log</h1>
<ul id="log"></ul>

fiddle.js

/**
 * User constructor.
 */

function User(firstName, lastName) {
  this.firstName = firstName;
  this.lastName = lastName;
}

/**
 * Set `User` prototype functions.
 */

!function(proto) {

  /**
   * Returns full name. (pseudo private function)
   * 
   * @return {String} Full name
   * @api private
   */
  
  function _buildFullname() {
    return this.firstName + " " + this.lastName;
  }
  
  /**
   * Returns initial. (pseudo private function)
   * 
   * @param {String} firstName
   * @param {String} lastName
   * @return {String} Initial
   * @api private
   */
  
  function _buildInitial(firstName, lastName) {
    return firstName.slice(0, 1) + "." + lastName.slice(0, 1) + ".";
  }
  
  /**
   * Full name getter function.
   * 
   * @return {String} Full name.
   * @api public
   */
  
  proto.getFullname = function() {
    return _buildFullname.call(this);
  };
  
  /**
   * Initial getter function.
   * 
   * @return {String}
   * @api public
   */
  proto.getInitial = function() {
    return _buildInitial(this.firstName, this.lastName);
  };

}(User.prototype);

/**
 * Usage.
 */

$(function() {
  
  /**
   * Logger
   * 
   * @param {String} message
   */
  
  function log(message) {
    if (console) {
      console.log(message);
    }
    $('#log').append($('<li>' + message + '</li>'));
  }
  
  log('=== start ===');
  
  var user = new User('Seiya', 'Konno');
  log(user.getFullname());
  log(user.getInitial());
  
  try {
    log(user._buildFullname()); // can't call pseudo private function.
  } catch (e) {
    log(e.message);
  }
  
  log('=== finish ===');
});

fiddle.manifest

name: pseudo private function
description: pseudo private function
authors:
  - Seiya Konno

log.txt

=== start ===
Seiya Konno
S.K.
Object # has no method '_buildFullname'
=== finish ===

http://jsfiddle.net/gh/gist/jquery/1.7.1/1852850/