Pseudo private function using `Function.prototype.bind`

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

}(User.prototype);