How to create my own module of functions in a node.js app

Question

I'm building my node.js app which has the following structure:

server.js
controllers/user.js

server.js require the user.js controller with:

require('./controllers/user.js').route(app, mongoose);

the controller/user.js file is like:

function route(app, mongoose){
   function route(app, mongoose){

   // Create new User item
   app.post('/user/create', function(req, res){
     ...
   }

   // Edit user
   app.put('/user/:id/edit', function(req, res){
    ...
   }

   ...
}
module.exports.route = route;

This is working fine. I know want to had middleware in the Edit user function for instance so it looks like:

...
app.put('/user/:id/edit', loadUser, function(req, res){
...

If I define loadUser function right above this line it's working fine. When I add all the middleware fonction in a file './lib/middleware.js' and when I try to load that file in user.js with:

require('../lib/middleware.js').create(); // Create is the exported function

this does not work and I have the error message saying that loadUser is an unknow function.

Any idea ?

** UPDATE **

I have updated the files such that, in server.js (main file) I have:

...
var middleware = require('./lib/middleware.js');
...
require('./controllers/user.js').route(app, mongoose, middleware);
...

In middleware.js, I then have:

function create() {
  function loadUser(req, res, next) {
    // You would fetch your user from the db
    var user = users[req.params.id];
    if (user) {
      req.user = user;
      next();
    } else {
      next(new Error('Failed to load user ' + req.params.id));
    }
  }
return module;
}

In controllers/user.js I have

function route(app, mongoose, middleware){
   ...
   // Modify an user
   app.put('/user/edit', middleware.loadUser, function(req, res){
     ...
   }
   ...
}

When I run the app (node server.js) I then have the following error:

Error: PUT route /user/edit requires a callback

I am not sure to return the correct thing within middleware.js, not really familiar with module stuff yet. I also tried the "module.exports.create = create;" but same thing.

UPDATE WITH ANOTHER TRY

what if I create a module for the function ? In ./lib/middleware.js I would have:

(function(){
  var middleware = {};
  middleware.loadUser = function () {
  console.log("loadUser");
  }
  return middleware;
}());

And in server, I call it:

var middleware = require('./lib/middleware.js');
middleware.loadUser;

It seems to me that should work but it does not...

As to your second example remember require returns module.exports not module so change it to module.exports = middleware instead of return middleware. See Edit to answer. — Raynos
– Raynos, Commented Apr 14, 2011 at 13:19

Raynos · Accepted Answer · 2011-04-14 13:22:38Z

4

"global" scope in a file is actually module scope. Just by creating a function in a different file it does become in scope in your original file.

What you want to do instead is

// routes.js
var middleware = require("../lib/middleware.js").create();

app.put('/user/:id/edit', middelware["loadUser"], function(req, res){

You will find that global variables actually write to module in their scope.

Then your function loadUser() { ... } should exist in the module property.

// middleware.js
function create() { 
    ...

    return module;
}

If you return module from your create function your returning global scope.

[Edit]

function create() {
  function loadUser(req, res, next) {
    // You would fetch your user from the db
    var user = users[req.params.id];
    if (user) {
      req.user = user;
      next();
    } else {
      next(new Error('Failed to load user ' + req.params.id));
    }
  }
return module;
}

You either need to add module.loadUser = loadUser or define loadUser in module scope. I.e. outside the create function.

[Further Edit]:

A standard setup would be something like:

// middleware.js
(function() {

    function loadUser(...) {
        ...
    }

    ...

    module.exports.loadUser = loadUser;

})();

//otherfile.js
var middle = require("middleware");
middle.loadUser();

edited Apr 14, 2011 at 13:22

answered Apr 13, 2011 at 22:37

Raynos

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3 Comments

Luc Over a year ago

I added another try in the questions as I do not really know if the create function is required. Why not using a module ?

Luc Over a year ago

it works !!! Great. thanks a lot. In my last example I used middle.loadUser; (without the () ).

Anderson Green Over a year ago

BTW, is there any way to distribute node.js modules using npm?

dnewcome · Accepted Answer · 2011-04-13 22:59:14Z

1

When code is loaded using require() it doesn't put anything into the global context. You have to bind it to a variable.

For example when you require your middleware file, you are able to call create() only because the module.exports object is returned from the require() function and you are able to access the call site directly. Here is how you would keep a reference to the require()d code so you could access it later:

var middleware = require('../lib/middleware.js');
middleware.create();

and probably this is what you want:

app.put('/user/:id/edit', middleware.loadUser, function(req, res) ...

update: As raynos pointed out, no function wrapper is advised in this case. See his comment.

~~Note that I wrapped the loadUser function reference in an anonymous function. Leaving the code as you had it would have worked as long as your code didn't rely on the value of 'this' internally.~~

update: I think I misunderstood what you were trying to do with create(). The above works if you define your loadUser() function as directly part of the module. If you need to do something else tricky in your Create() function you can use what I wrote above by doing something like

var loadUser = middleware.create();

Then you'll have the loadUser function defined in scope.

edited Apr 13, 2011 at 22:59

answered Apr 13, 2011 at 22:36

dnewcome

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4 Comments

Raynos Over a year ago

actually the module.exports object is returned from the require call. Also why wrap it in a function when you can pass in middleware.loadUser to app.put

Raynos Over a year ago

Also the middleware object is module.exports so loadUser has to be defined in module.exports. if it's just defined in module scope it will not work.

dnewcome Over a year ago

I meant to say exports, I'll correct it. As for the function, since it doesn't make sense to preserve the call target in this case I agree it is not necessary. I made the assumption which I corrected in my answer that the loadUser function was exported from the module.

Luc Over a year ago

@Raynos, I updated the question with my last tests but still the same thing. Do you have any idea of what I've done wrong ?

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