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.

Answer 3

Like I said in the comments, you can use a function as module.exports. A function is also an object, so you don't have to change your syntax.

app.js

var controllers = require('./controllers')({app: app});

controllers.js

module.exports = function(params)
{
    return require('controllers/index')(params);
}

controllers/index.js

function controllers(params)
{
  var app = params.app;

  controllers.posts = require('./posts');

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

module.exports = controllers;

Answer 4

Or just do that:

var app = req.app

inside the Middleware you are using for these routes. Like that:

router.use( (req,res,next) => {
    app = req.app;
    next();
});

Answer 5

1. To make your db object accessible to all controllers without passing it everywhere: make an application-level middleware which attachs the db object to every req object, then you can access it within in every controller.

// app.js
let db = ...;  // your db object initialized
const contextMiddleware = (req, res, next) => {
  req.db=db;
  next();
};
app.use(contextMiddleware);

2. to avoid passing app instance everywhere, instead, passing routes to where the app is

// routes.js  It's just a mapping.
exports.routes = [
  ['/', controllers.index],
  ['/posts', controllers.posts.index],
  ['/posts/:post', controllers.posts.show]
];

// app.js
var { routes }    = require('./routes');
routes.forEach(route => app.get(...route));
// You can customize this according to your own needs, like adding post request

The final app.js:

// app.js
var express   = require('express');
var app       = express.createServer();

let db = ...;  // your db object initialized
const contextMiddleware = (req, res, next) => {
  req.db=db;
  next();
};
app.use(contextMiddleware);

var { routes }    = require('./routes');
routes.forEach(route => app.get(...route));

app.listen(3000, function() {
  console.log('Application is listening on port 3000');
});

Another version: you can customize this according to your own needs, like adding post request

// routes.js  It's just a mapping.
let get = ({path, callback}) => ({app})=>{
  app.get(path, callback);
}
let post = ({path, callback}) => ({app})=>{
  app.post(path, callback);
}
let someFn = ({path, callback}) => ({app})=>{
  // ...custom logic
  app.get(path, callback);
}
exports.routes = [
  get({path: '/', callback: controllers.index}),
  post({path: '/posts', callback: controllers.posts.index}),
  someFn({path: '/posts/:post', callback: controllers.posts.show}),
];

// app.js
var { routes }    = require('./routes');
routes.forEach(route => route({app}));

Answer 6

Let's say that you have a folder named "contollers".

In your app.js you can put this code:

console.log("Loading controllers....");
var controllers = {};

var controllers_path = process.cwd() + '/controllers'

fs.readdirSync(controllers_path).forEach(function (file) {
    if (file.indexOf('.js') != -1) {
        controllers[file.split('.')[0]] = require(controllers_path + '/' + file)
    }
});

console.log("Controllers loaded..............[ok]");

... and ...

router.get('/ping', controllers.ping.pinging);

in your controllers forlder you will have the file "ping.js" with this code:

exports.pinging = function(req, res, next){
    console.log("ping ...");
}

And this is it....

Answer 7

If you want to pass an app-instance to others in Node-Typescript :

Option 1: With the help of import (when importing)

//routes.ts
import { Application } from "express";
import { categoryRoute } from './routes/admin/category.route'
import { courseRoute } from './routes/admin/course.route';

const routing = (app: Application) => {
    app.use('/api/admin/category', categoryRoute)
    app.use('/api/admin/course', courseRoute)
}
export { routing }

Then import it and pass app:

import express, { Application } from 'express';

const app: Application = express();
import('./routes').then(m => m.routing(app))

Option 2: With the help of class

// index.ts
import express, { Application } from 'express';
import { Routes } from './routes';


const app: Application = express();
const rotues = new Routes(app)
...

Here we will access the app in the constructor of Routes Class

// routes.ts
import { Application } from 'express'
import { categoryRoute } from '../routes/admin/category.route'
import { courseRoute } from '../routes/admin/course.route';

class Routes {
    constructor(private app: Application) {
        this.apply();
    }

    private apply(): void {
       this.app.use('/api/admin/category', categoryRoute)
       this.app.use('/api/admin/course', courseRoute)
    }
}

export { Routes }

Answer 8

var express = require('express');

var router = express.Router();

router.get('/', function(req, res, next) {
   console.log(req.app); // use req.app to get app instance ;

   res.render('index', { title: 'Express' });

});

module.exports = router;

Answer 9

For database separate out Data Access Service that will do all DB work with simple API and avoid shared state.

Separating routes.setup looks like overhead. I would prefer to place a configuration based routing instead. And configure routes in .json or with annotations.