# Simple Engineering

## Modularizing nodejs applications ~ Manifest routes

We assume most of the system components to be accessible for testability. However, that is challenging when routes are a little bit complex. To reduce the complexity that comes with working on large-scale expressjs routes, we will apply a technique known as manifest routes to make route declarations change proof, making them more stable as the rest of the application evolves.

• The need to have manifest routes technique
• How to apply the manifest routes as a modularization technique

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## Show me the code

var express = require('express')
var app = express();

app.get('/', function(req, res, next) {
res.render('index', { title: 'Express' });
});

/** code that initialize everything, then comes this route*/
app.get('/users/:id', function(req, res, next){
User.findById(req.params.id, function(error, user){
if(error) return next(error);
return res.status(200).json(user);
});
});

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



## What can possibly go wrong?

When trying to figure out how to approach modularization of expressjs routes with a manifest route pattern, the following points may be a challenge:

• Where to start with modularization without breaking the rest of the application
• How to introduce the layered architecture, without incurring additional test burden, but making it easier to isolate tests

The following sections will explore more on making points stated above work.

## The need to have manifest routes technique

There is a subtle nuance that is missing when following traditional approaches to modularization.

When adding an index file, as a part of the modularization process, exporting the content of directories, for that matter — sub-directories, does not result in exporting routes that can be plugged into existing expressjs applications.

The remedy is to create, isolate, export, and manifest them to the outer world.

## How to apply the manifest routes handlers for reusability

The handlers are a beast in their own way.

A collection of related route handlers can be used as a baseline to create the controller layer. The modularization of this newly created/revealed layer can be achieved in two steps as was the case for other use cases. The first step consists of naming, ejecting, and exporting single functions as modules. The second step consists of adding an index to every directory and exporting the content of the directory.

## Manifest routes

In essence, requiring a top-level directory, will seek for index.js at top of the directory and make all the route content accessible to the caller.

var routes = require('./routes');


Example: /routes has index.js at top level directory ~ source

A typical default entry point of the application:

var express = require('express');
var router = express.Router();

router.get('/', function(req, res, next) {
return res.render('index', { title: 'Express' });
});
module.exports = router;


Example: default /index entry point

Anatomy of a route handler

module.exports = function (req, res) {  };


Example: routes/users/get-user|new-user|delete-user.js

“The most elegant configuration that I've found is to turn the larger routes with lots of sub-routes into a directory instead of a single route file” – Chev source

When individual routes/users sub-directories are put together, the resulting index would look as in the following code sample

var router = require('express').Router();
router.get('/get/:id', require('./get-user.js'));
router.post('/new', require('./new-user.js'));
router.post('/delete/:id', require('./delete-user.js'));
module.exports = router;


Example: routes/users/index.js

Update when routes/users/favorites/ adds more sub-directories

router.use('/favorites', require('./favorites'));
...
module.exports = router;


Example: routes/users/index.js ~ after adding a new favorites requirement

We can go extra mile and group route handlers in controllers. Using route and controllers' route handler as a controller would look as in the following example:

var router = require('express').Router();
var catalogues = require('./controllers/catalogues');

router.route('/catalogues')
.get(catalogues.getItem)
.post(catalogues.createItem);
module.exports = router;


## Conclusion

Modularization makes expressjs routes reusable, composable, and stable as the rest of the system evolves. Modularization brings elegance to route composition, improved testability, and reduces instances of redundancy.

In this article, we revisited a technique that improves expressjs routes elegance, their testability, and re-usability known under the manifest route moniker. We also re-state that the manifest route technique is an extra mile to modularizing expressjs routes. There are additional complimentary materials in the “Testing nodejs applications” book.