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Node.js make initialized object available in all modules

I have an initialized object that I initialized in app.js file and I would like to make this initialized object is available in all modules. How could I do that? Passing this object to every modules is one way to do and I'm wondering if I'm missing anything or there should be done in difference ways?
I saw mongoose actually support default connection, which I need to init in app.js one time and anywhere in other modules, I can just simply use it without requiring passing it around. Is there any I can do the same like this?
I also checked global object doc from node.js http://nodejs.org/api/globals.html, and wondering I should use global for issue.
Thanks

A little advice:
You should only very rarely need to use a global. If you think you need one, you probably don't.
Singletons are usually an anti-pattern in Node.js, but sometimes (logging, config) they will get the job done just fine.
Passing something around is sometimes a useful and worthwhile pattern.
Here's an example of how you might use a singleton for logging:
lib/logger.js
var bunyan = require('bunyan'),
mixIn = require('mout/object/mixIn'),
// add some default options here...
defaults = {},
// singleton
logger,
createLogger = function createLogger(options) {
var opts;
if (logger) {
return logger;
}
opts = mixIn({}, defaults, options);
logger = bunyan.createLogger(opts);
return logger;
};
module.exports = createLogger;
lib/module.js
var logger = require('./logger.js'),
log = logger();
log.info('Something happened.');
Hope that helps.

The solution, as you suggest is to add the object as a property to the global object. However, I would recommend against doing this and placing the object in its own module that is required from every other module that needs it. You will gain benefits later on in several ways. For one, it is always explicit where this object comes from and where it is initialized. You will never have a situation where you try to use the object before it is initialized (assuming that the module that defines it also initializes it). Also, this will help make your code more testable,

There are multiple solutions to the problem, depends upon how large your application is. The two solutions that you have mentioned are the most obvious ones. I would rather go for the third which is based on re-architecturing your code. The solution that I am providing looks alot like the executor pattern.
First create actions which require your common module that are in this particular form -
var Action_One = function(commonItems) {
this.commonItems = commonItems;
};
Action_One.prototype.execute = function() {
//..blah blah
//Your action specific code
};
var Action_Two = function(commonItems) {
this.commonItems = commonItems;
};
Action_Two.prototype.execute = function() {
//..blah blah
//Your action_two specific code
};
Now create an action initializer which will programmatically initialize your actions like this -
var ActionInitializer = function(commonItems) {
this.commonItems = commonItems;
};
ActionInitializer.prototype.init = function(Action) {
var obj = new Action(this.commonItems);
return obj;
};
Next step is to create an action executor -
//You can create a more complex executor using `Async` lib or something else
var Executor = function(ActionInitializer, commonItems) {
this.initializer = new ActionInitializer(commonItems);
this.actions = [];
};
//Use this to add an action to the executor
Executor.prototype.add = function(action) {
var result = this.initializer.init(action);
this.actions.push(result);
};
//Executes all the actions
Executor.prototype.executeAll = function() {
var result = [];
for (var i = this.action.length - 1; i >= 0; i--) {
result[i] = this.action[i].execute();
}
this.action = []
return result;
};
The idea was to decouple every module so that there is only one module Executor in this case which is dependent on the common properties. Now lets see how it would work -
var commonProperties = {a:1, b:2};
//Pass the action initilizer class and the common property object to just this one module
var e = new Executor(ActionInitializer, commonProperties);
e.add(Action_One);
e.add(Action_Two);
e.executeAll();
console.log(e.results);
This way your program will be cleaner and more scalable. Shoot questions if it's not clear. Happy coding!

Overriding methods using Javascript module pattern

I've got a browser addon I've been maintaining for 5 years, and I'd like to share some common code between the Firefox and Chrome versions.
I decided to go with the Javascript Module Pattern, and I'm running into a problem with, for example, loading browser-specific preferences, saving data, and other browser-dependent stuff.
What I'd like to do is have the shared code reference virtual, overrideable methods that could be implemented in the derived, browser-specific submodules.
Here's a quick example of what I've got so far, that I've tried in the Firebug console, using the Tight Augmentation method from the article I referenced:
var core = (function(core)
{
// PRIVATE METHODS
var over = function(){ return "core"; };
var foo = function() {
console.log(over());
};
// PUBLIC METHODS
core.over = over;
core.foo = foo;
return core;
}(core = core || {}));
var ff_specific = (function(base)
{
var old_over = base.over;
base.over = function() { return "ff_specific"; };
return base;
}(core));
core.foo();
ff_specific.foo();
Unfortunately, both calls to foo() seem to print "core", so I think I've got a fundamental misunderstanding of something.
Essentially, I'm wanting to be able to call:
get_preference(key)
set_preference(key, value)
load_data(key)
save_data(key, value)
and have each browser do their own thing. Is this possible? Is there a better way to do it?

In javascript functions have "lexical scope". This means that functions create their environment - scope when they are defined, not when they are executed. That's why you can't substitute "over" function later:
var over = function(){ return "core"; };
var foo = function() {
console.log(over());
};
//this closure over "over" function cannot be changed later
Furthermore you are "saying" that "over" should be private method of "core" and "ff_specific" should somehow extend "core" and change it (in this case the private method which is not intended to be overridden by design)

you never override your call to foo in the ff_specific code, and it refers directly to the private function over() (which never gets overridden), not to the function core.over() (which does).
The way to solve it based on your use case is to change the call to over() to be a call to core.over().
That said, you're really confusing yourself by reusing the names of things so much, imo. Maybe that's just for the example code. I'm also not convinced that you need to pass in core to the base function (just to the children).

Thanks for your help. I'd forgotten I couldn't reassign closures after they were defined. I did figure out a solution.
Part of the problem was just blindly following the example code from the article, which meant that the anonymous function to build the module was being called immediately (the reusing of names Paul mentioned). Not being able to reassign closures, even ones that I specifically made public, meant I couldn't even later pass it an object that would have its own methods, then check for them.
Here's what I wound up doing, and appears to work very well:
var ff_prefs = (function(ff_prefs)
{
ff_prefs.foo = function() { return "ff_prefs browser specific"; };
return ff_prefs;
}({}));
var chrome_prefs = (function(chrome_prefs)
{
chrome_prefs.foo = function() { return "chrome_prefs browser specific"; };
return chrome_prefs;
}({}));
var test_module = function(extern)
{
var test_module = {};
var talk = function() {
if(extern.foo)
{
console.log(extern.foo());
}
else
{
console.log("No external function!");
}
};
test_module.talk = talk;
return test_module;
};
var test_module_ff = new test_module(ff_prefs);
var test_module_chrome = new test_module(chrome_prefs);
var test_module_none = new test_module({});
test_module_ff.talk();
test_module_chrome.talk();
test_module_none.talk();
Before, it was running itself, then when the extension started, it would call an init() function, which it can still do. It's just no longer an anonymous function.

Breaking my javascript into modules, am I doing this right?

I'm using the javascript module pattern, and have this so far:
var APP;
if(APP == undefined) {
APP = {};
}
APP = (function() {
var userId = -1;
var privateVar = '';
var _init = function($userId) {
userId = $userId;
};
var _publicMethod = function($id){
privateVar = id;
};
return {
init = function($userId) {
_init($userId);
},
publicMethod = function($id) {
_publicMethod($id);
}
};
})();
I then have a common utils module:
APP.utils = (function(){
})();
And then per page I am planning on having a module, so I don't wireup events (button clicks etc) for no reason on pages where these DOM elements don't event exist:
APP.homePage = (function(){
return {
};
})();
So each module will have a init() method that I will call on the page to run things that have to be run (e.g. wiring up events, setting variables like say userId etc):
$(document).ready(function() {
APP.init(<%= user.id %>);
APP.homePage.init('abc');
});
So now if the files get too big, I can break them out into separate files also.
What if one module needs to call another, I guess the only way for this to work is to do this via the public api right?
e.g. what if homePage needs userId, should I pass that in the homePage#init method?
How is my coding style, any obvious style that is not considered best practise?
Any comments on this approach? Is it good in general?

What if one module needs to call another, I guess the only way for this to work is to do this via the public api right?
Yes
e.g. what if homePage needs userId, should I pass that in the homePage#init method?
No. I'd not repeat the userId code in all modules, but offer a public getter for it in the default module.
Any comments on coding
This code
var APP;
if(APP == undefined) {
APP = {};
}
APP = ...
is quite useless. You don't need to check for object existance here, because you overwrite it anyway. That also means that this code must be the first to execute. If you want to make the modules independent from load order, you'd need to use something like
var APP = (function(a) {
var private_vars; // ...
a.init = ...
a.publicMethod = ... // add them to the object instead of creating new one
a.getPrivate = function() {
return private_vars;
};
return a;
})(APP || {}); // create one iff not already existing
// other file:
var APP = APP || {};
APP.utils = ... // add object to namespace
The code
var _publicMethod = function($id){
privateVar = id;
};
looks a bit odd. First, the underscore usually denotes a semiprivate (public-but-not-to-be-used) attribute of objects and should not be used for variable names. That's not the case in here as the function will be exposed as the "publicmethod" property of APP. Use the underscore there if you want it. Second, there is no need to use a function expression here. The code is in the module's local scope, and using a function declaration both makes it available everywhere in that scope and allows naming the function. You should use
function publicMethod($id) {
privateVar = id;
}
a.publicMethod = publicMethod;

The module pattern is, in my opinion, a really nice way to organize your code. To answer your questions:
1) Yes, your modules can only access methods and properties of other modules which have been exposed in the object they return.
2) I think your coding style looks pretty good. I'd make these changes:
APP = (function() {
var _userId = -1;
var _privateVar = '';
var init = function($userId) {
_userId = $userId;
};
var publicMethod = function($id){
_privateVar = id;
};
return {
init : init,
publicMethod : _publicMethod
};
})();
First, underscores are generally meant to denote "private" properties or methods. Secondly, you can do away with the extra functions in the object being returned and just point straight to the methods or properties you care about. This is generally referred to as the "Revealing Module Pattern", because even the public methods aren't defined within the returned object - they're simply referenced.
3) This approach is definitely a nice way to encapsulate code. You get the benefit of private and privileged methods, and you generally end up with a nicer API because you're only exposing things that need to be public.
Well done.

JavaScript Module Pattern - Protected members?

Hullo! This is my first question!
I am experimenting with the module pattern promoted by Doug Crockford and others. Mostly very happy with it so far, but I am a little unsure about the best way of handling a certain inheritance pattern.
I have it boiled down to a bare bones case using cat and mammal, although my actual intention is to make objects for a tile based game in canvas.
But here is my bare bones 'animals' case using a browser alert:
var ZOO = ZOO || {};
//
ZOO.mammal = function () {
"use strict";
var voice = "squeak.mp3", // default mammal sound
utter = function () {
window.alert(this.voice);
};
//
// public interface
return {
utter: utter,
voice: voice
};
};
//
ZOO.cat = function () {
"use strict";
// hook up ancestor
var thisCat = ZOO.mammal();
thisCat.voice = "miaw.mp3";
return thisCat;
};
//
var felix = ZOO.cat();
felix.utter();
What bothers me about this approach is that I have had to make voice a public property so that cat can modify it.
What I really want is something like 'protected' visibility (from Java, ActionScript etc.), so that cat can modify voice without anyone with access to felix being able to modify it.
Is there a solution?

You can simulate protected visibility (visible to yourself, and child objects) by passing a blank object to your base "class" to serve as the repository for your protected properties. This will allow you to share properties through your inheritance chain, without making them public.
var ZOO = ZOO || {};
ZOO.mammal = function (protectedInfo) {
"use strict";
protectedInfo = protectedInfo || {};
protectedInfo.voice = "squeak.mp3";
// public interface
return {
utter: function () {
alert(protectedInfo.voice);
}
};
};
ZOO.cat = function () {
"use strict";
var protectedInfo = {};
// hook up ancestor
var thisCat = ZOO.mammal(protectedInfo);
protectedInfo.voice = "miaw.mp3";
return thisCat;
};
Here's a live demo

Sidesteping non-answer:
There are some ways to kind of get protected properties in Javascript but they aren't necessarily very idiomatic. If I were you I would first strongly consider either
Using the convention of public properties prefaced with an underscore (ex.: _voice) to denote privacy. Its very simple and is something of a standard among dynamic languages.
Seek an alternate solution without inheritance. Inheritance often complicates and couples stuff to much, hence the old "prefer composition over inheritance" mantra. Javascript has many features, like duck typing and higher order functions, that often let you avoid using inheritance in situations where you would normaly need it in Java

There is a workaround to simulate protected members, where you make public those members for a while, and then you privatise them again. I'm not a big fan of this, but it's a "solution".
I'm just quoting from this SitePoint article:
Adding Protected Members
Splitting a script into multiple modules is a common and convenient
practice. It makes a large codebase much easier to manage, and allows
for bandwidth savings to be made when modules aren’t always required.
But what if we want to share data between different modules? If we
make that data public then we’ll lose the benefits of privacy, but if
we make it private it will only be available to one module. What we
really need are shared private members, and these are known as
protected.
JavaScript doesn’t have protected members as such, but we can
effectively create them by making data temporarily public. To achieve
this, let me first introduce you to two key functions — extend and
privatise — which we’ll define as part of a utility-functions object:
var utils = {
extend : function(root, props) {
for(var key in props) {
if(props.hasOwnProperty(key)) {
root[key] = props[key];
}
} return root;
},
privatise : function(root, prop) {
var data = root[prop];
try { delete root[prop]; } catch(ex) { root[prop] = null; }
return data;
}
};
The extend function simply adds new properties to an object, while the
privatise function copies a property and then deletes the original. We
can use extend in one module to create a public reference to a private
variable, and then use privatise in another module to copy it back to
a private variable and delete the public reference.
So here’s an example of the first module which has two protected
members (including the utils object itself), and one public member. To
keep the code example short, the utility functions are just empty
shells, but they would be identical to the functions I showed you a
moment ago:
var MyModule = (function() {
var myProtectedData = 909;
var utils = {
extend : function(root, props) { },
privatise : function(root, prop) { }
};
this.myPublicData = 42;
return utils.extend(this, { myProtectedData : myProtectedData, utils : utils });
})();
You can see how we’re using a variant of the revealing module pattern,
to return not just the public members, but the protected members as
well. So at this point we have three public members:
MyModule.myProtectedData, MyModule.utils and MyModule.myPublicData.
Now here’s an example of the last module which uses the privatise
function to copy the specified public members back to private
variables, and then delete their public references:
var MyModule = (function() {
var myProtectedData = this.utils.privatise(this, 'myProtectedData');
var utils = this.utils.privatise(this, 'utils');
return this;
}).apply(MyModule);
And once that’s done the protected members are locked inside their
objects, privately available to both the modules, but no longer
available from outside them.
Note that the privatise function relies on having separate arguments
for the object and the property-key, because objects in JavaScript are
passed by reference. So root is a reference to MyModule, and when we
delete a property from it that’s specified by key, we’re deleting that
property from the referenced object.
But if it was like this:
privatise : function(root) {
var data = root;
try { delete root; } catch(ex) { root = null; } return data;
}
And called like this:
var myProtectedData = this.utils.privatise(this.myProtectedData);
Then the public members would not be deleted — the function would
simply delete the reference, not the property it refers to.
The try ... catch construct is also necessary for older IE versions,
in which delete is not supported. In that case we nullify the public
property rather than deleting it, which is obviously not the same, but
has an equivalent end result of negating the member’s public
reference.

Is this a good structure for my jQuery scripts?

I want to keep my scripts organized in one .js file for all my site (I have a mess right now), something like namespaces and classes in C#...
(function ($) {
//private variables
$.divref = $("#divReference");
//Namespaces
window.MySite = {};
window.MySite.Home = {};
window.MySite.Contact = {};
//Public function / method
window.MySite.Home.Init = function(params){
alert("Init");
MySite.Home.PrivateFunction();
$.divref.click(function(){
alert("click");
});
};
//private function / method
MySite.Home.PrivateFunction = function(){
alert("Private");
};
})(jQuery);
Is this an idiomatic layout in jQuery and JScript?

I'll go ahead and post my comment as an answer, though I'm not 100% it addresses your questions about c# namespaces and their parallels in JavaScript (I'm no c# programmer). You're not actually creating private variables because you're attaching them to the $ Object that will exist after this function finishes. If you want private variables you need to use a closure. Those look something like this:
var myObject = function () {
var innerVariable = 'some private value';
return {
getter: function () {
return innerVariable;
}
}
}()
If you attempt to access myObject.innerVariable it will return undefined but if you call myObject.getter() it will return the value correctly. This concept is one you will want to read up on in JavaScript, and for programming in general. Hope that helps.

This is more how I would implement the pattern you are trying to do:
// MySite.Home Extension
window.MySite =
(function ($, root) {
//private variables
var $divref = $("#divReference");
//private function / method
var privateFunction = function(){
alert("Private");
};
root.Home = {};
// Public variable
root.Home.prop = "Click"
//Public function / method
root.Home.Init = function(params){
alert("Init");
private();
$divref.click(function(){
alert(root.Home.prop);
});
};
return root;
})(jQuery, window.MySite || {} );
// MySite.Contact Extension
window.MySite =
(function ($, root) {
root.Contact = {};
// More stuff for contact
return root;
})(jQuery, window.MySite || {} );
The first change is splitting each "namespace" into its own Module pattern, so private variables wont bleed from namespace to namespace (if you do intend them to be private to the namespace, which would be more C# esque). Second is rather than accessing window.MySite, pass in the object that you want to extend (in this case I'm calling it root). This will give you some flexibility.
Your private methods weren't really private. To make a private method, you just want to make a function var that it bound in the closure, but not assigned to a property on the externally visible object. Lastly, you probably don't want to use $.somegarbage. Like mentioned in a comment, you are adding a property to the $ object, which will still be there when the closure is done. If you wanted something close, I would just use $somegarbage which some people seem to like to do, but any variable name will work for private variables, just as long as the variable is bound in the closures scope (not somewhere else)
You are on the right track...

you might want to read up on the Module pattern (more) and closures in javascript to prevent polluting the global namespace.