Express: How to pass app-instance to routes from a different file?

Question

I want to split up my routes into different files, where one file contains all routes and the other one the corresponding actions. I currently have a solution to achieve this, however I need to make the app-instance global to be able to access it in the actions. My current setup looks like this:

app.js:

var express   = require('express'); var app       = express.createServer(); var routes    = require('./routes');  var controllers = require('./controllers'); routes.setup(app, controllers);  app.listen(3000, function() {   console.log('Application is listening on port 3000'); }); 

routes.js:

exports.setup = function(app, controllers) {    app.get('/', controllers.index);   app.get('/posts', controllers.posts.index);   app.get('/posts/:post', controllers.posts.show);   // etc.  }; 

controllers/index.js:

exports.posts = require('./posts');  exports.index = function(req, res) {   // code }; 

controllers/posts.js:

exports.index = function(req, res) {   // code };  exports.show = function(req, res) {   // code }; 

However, this setup has a big issue: I have a database- and an app-instance I need to pass to the actions (controllers/*.js). The only option I could think of, is making both variables global which isn't really a solution. I want to separate routes from the actions because I have a lot of routes and want them in a central place.

What's the best way to pass variables to the actions but separate the actions from the routes?

Answer 1

Use req.app, req.app.get('somekey')

The application variable created by calling express() is set on the request and response objects.

See: https://github.com/visionmedia/express/blob/76147c78a15904d4e4e469095a29d1bec9775ab6/lib/express.js#L34-L35

Answer 2

Node.js supports circular dependencies.
Making use of circular dependencies instead of require('./routes')(app) cleans up a lot of code and makes each module less interdependent on its loading file:

---

app.js

var app = module.exports = express(); //now app.js can be required to bring app into any file  //some app/middleware setup, etc, including  app.use(app.router);  require('./routes'); //module.exports must be defined before this line 

---

routes/index.js

var app = require('../app');  app.get('/', function(req, res, next) {   res.render('index'); });  //require in some other route files...each of which requires app independently require('./user'); require('./blog'); 

---

-----04/2014 update-----
Express 4.0 fixed the usecase for defining routes by adding an express.router() method!
documentation - http://expressjs.com/4x/api.html#router

Example from their new generator:
Writing the route:
https://github.com/expressjs/generator/blob/master/templates/js/routes/index.js
Adding/namespacing it to the app: https://github.com/expressjs/generator/blob/master/templates/js/app.js#L24

There are still usecases for accessing app from other resources, so circular dependencies are still a valid solution.