private_properties.js

var new_user = function (attribs) {
  var secretPassword;         // private attribute
  var user = attribs;         // object we will return
  // public properties and methods:
  user.setPassword = function (newPassword) {
    secretPassword = newPassword;
  }
  user.checkPassword = function (tryPassword) {
      return (tryPassword == secretPassword);
  }
  return (user);
};
dave = new_user({name: 'dave'}).setPassword('patterson');
dave.checkPassword('patt');      // => false
dave.checkPassword('patterson'); // => true
dave.secretPassword;             // => undefined