JavaScript Observer Pattern - Module Pattern implementation

gistfile1.js

var Observable = (function()
{
    "use strict";

    /**
     * @constructor
     * @returns {{attach: Function, detach: Function, notify: Function}}
     */
    var constructor = function()
    {
        /**
         * @private
         * @type {Array}
         */
        var observers = [];

        /**
         * @param observer {Observable}
         * @param event {string}
         */
        function attach(observer, event)
        {
            observers.push({
                observer : observer,
                event    : event
            });
        }

        /**
         * @param observer {Observable}
         */
        function detach(observer)
        {
            for(var i = 0, l = observers.length; i < l; i++)
            {
                if(observers[i].observer === observer)
                {
                    observers.splice(i, 1);
                    i--;
                }
            }
        }

        /**
         * @param event {string}
         * @param data {object}
         */
        function notify(event, data)
        {
            var item;
            for(var key in observers)
            {
                item = observers[key];
                if(!(item.event !== undefined && item.event !== event))
                {
                    item.observer.notify(event, data);
                }
            }
        }

        return {
            attach : attach,
            detach : detach,
            notify : notify
        }
    }

    return constructor;
})();

var Users = (function()
{
    "use strict";

    /**
     * @constructor
     * @returns {{addUser: Function, removeUser: Function}}
     */
    var constructor = function()
    {
        /**
         * @private
         * @type {object}
         */
        var users = {};

        /**
         * @param username {string}
         * @param email {string}
         * @param address {string}
         * @param postcode {string}
         */
        function addUser(username, email, address, postcode)
        {
            users[username] = {
                username : username,
                email    : email,
                address  : address,
                postcode : postcode
            }
            this.notify(constructor.ADD_USER, users[username]);
        }

        /**
         * @param username {string}
         */
        function removeUser(username)
        {
            if(users[username] !== undefined)
            {
                this.notify(constructor.REMOVE_USER, users[username]);
                users[username] = undefined;
            }
            else
            {
                this.notify(constructor.ERROR, 'Removing user failed, username not found ' + username);
            }
        }

        var instance = new Observable();
        instance.addUser = addUser;
        instance.removeUser = removeUser;

        return instance;
    }

    constructor.ADD_USER = "addUser";
    constructor.REMOVE_USER = "removeUser";
    constructor.ERROR = "errorUser";

    return constructor;
})();

var SendEmailToNewUsers = (function()
{
    "use strict";

    /**
     * @constructor
     * @returns {Observable}
     */
    var constructor = function()
    {
        /**
         * @param event {string}
         * @param data {object}
         */
        function handleNotify(event, data)
        {
            if (event === Users.ADD_USER)
            {
                document.write('\n[sendmail] Added a user, sending email to ' + data['email']);
            }
            else if (event === Users.REMOVE_USER)
            {
                document.write('\n[sendmail] Removed a user, sending email to ' + data['email']);
            }
        }

        var instance = new Observable();
        instance.notify = handleNotify;
        return instance;
    }

    return constructor;
})();

var WelcomeNewUser = (function()
{
    "use strict";

    /**
     * @constructor
     * @returns {Observable}
     */
    var constructor = function()
    {
        /**
         * @param event {string}
         * @param data {object}
         */
        function handleNotify(event, data)
        {
            document.write('\n[welcome] Welcome aboard, ' + data['username']);
        }

        var instance = new Observable();
        instance.notify = handleNotify;
        return instance;
    }

    return constructor;
})();

var ErrorUser = (function()
{
    "use strict";

    /**
     * @constructor
     * @returns {Observable}
     */
    var constructor = function()
    {
        /**
         * @param event {string}
         * @param data {object}
         */
        function handleNotify(event, data)
        {
            document.write('\n[error] There was an error: ' + data);
        }

        var instance = new Observable();
        instance.notify = handleNotify;
        return instance;
    }

    return constructor;
})();

/**
 * Main code
 */

document.write('\n<pre>');
document.write('\nStarting test');

// Observable
var users = new Users();

// Observers
users.attach(new SendEmailToNewUsers());
users.attach(new WelcomeNewUser(), Users.ADD_USER);
users.attach(new ErrorUser(), Users.ERROR);

// Process users
users.addUser('Ian Ross', 'ianross@gmail.xxx', '66 London Street', 'PE1 2RF');
users.addUser('Mike Smith', 'mikes@gmail.xxx', '123 Main Road', 'PE2 6FX');
users.removeUser('Ian Ross');
users.addUser('John Wayne', 'jwayne@gmail.xxx', '999 Kansas Road', 'LE5 5AZ');
users.removeUser('Anthony McQuinn');
users.removeUser('John Wayne');

document.write('\nEnded test');
document.write('\n</pre>');