This is an example of how to use closures for a module pattern in JavaScript

Closures.js

/**
 *This function can be thought of as a 'class' to be instantiated
 *
 */
function User(){
  //private members
  var username;
  var password;
  
  //constructor
  function doLogin(user, pass){
    username = user;
    password = pass;
  }
  //accessor for username
  function retrieveUsername(){
    return username;
  }
  //publicly exposed functions
  var publicApi = {
    login: doLogin,
    getUsername: retrieveUsername
  }
  return publicApi;
}

var joe = User();

joe.login('IAmJoe', 'MeMeMe');
var username = joe.getUsername();
var chelle  = User();
chelle.login('chelle', 'iamchelle');
var username = joe.getUsername();
var user2 = chelle.getUsername();
console.log(username); //logs 'IAmJoe' 
console.log(user2); //logs 'chelle'