ExpressJS: Adding routes dynamically at runtime

Question

I want to be able to add new routes at runtime without restarting the server with NodeJS & ExpressJS. I made a similiar approach like in this article: https://alexanderzeitler.com/articles/expressjs-dynamic-runtime-routing/
Technically I'm able to add new files and logic at runtime likewise in the article, but the problem is that when no api route was matched I'll send a 404 JSON respond (as it is supposed to be).

I think the problem that I'm having is that my dynamically created routes are never reached, because static routes have priority over dynamically created routes. This means that the created routes will be mounted after error handling and therefore will never be reached. My Code in app.js

...

// Routes
app.use('/api/products', productRoutes);
app.use('/api/users', userRoutes);

...

/* This is where the dynamically created routes should be mounted */

// Error handling
app.use((req, res, next) => {
    const err = new Error('Not found');
    err.status = 404;
    next(err);
});

app.use((err, req, res, next) => {
    res.status(err.status || 500).json({error: {message: err.message}});
});

/* This is where the dynamic routes are mounted */

module.exports = app;

When I comment out the error handling I'm able to reach the routes which I created during runtime whereas with error handling I can only reach dynamically created routes after server restart which I want to avoid.
The problem is not solved with query params, because the dynamically added routes differ in logic, model properties, http methods/verbs and API endpoints. e.g.
GET/POST /api/{endpoint}
GET/POST /api/foo/{endpoint}
GET/PUT/DELETE /api/foo/bar/{endpoint}/:id

I think I basically need to either:
1) find a way to mount the dynamically created routes before the error handling - which I'm currently stuck at or
2) modify the route stack - which I have read is impractical, slow, bad practice and error prone
3) find an alternative solution

I hope someone can help me.
Thanks in advance

EDIT
Here is the code for the creation of new routes. The relevant endpoint is /api/databases/ in the POST method

const Database = require('../models/database');
const controller = require('./template/controller');
const creation = require('../Creation');

...

exports.createOne = (req, res, next) => {
  if (!creation.findFileInDirectory(`./backend/api/models/${req.body.name.singular}.js`) ||
      !creation.findFileInDirectory(`./backend/api/controllers/${req.body.name.singular}.js`) ||
      !creation.findFileInDirectory(`./backend/api/routes/${req.body.name.singular}.js`)) {
    controller.createOne(req, res, next, Database, {
      modelName: 'database',
    }, () => {
      //creation.createEndpoint(req.body.name, req.body.data, req.body.auth);
      creation.createEndpoint(req.body.name, req.body, req.body.auth);
    });
  } else {
    res.status(422).json({message: 'Endpoint exists already'});
  }
}

...

The controller in the snippet is just a modular controller file, which handles all of my CRUD Operations of all the endpoints of different models. Each route is split into models, controllers and routes to seperate and better maintain their logic.

In the POST method I first check whether the endpoint to be created already exists. If it does I respond with a 422 respond that the endpoint already exists. If it does not exist I create an entry mith my modular controller in the databases endpoint and create a model, controller & route for the endpoint which should be created.

The creation logic is the following:

const createEndpoint = (name, data, auth) => {
    createFile(`./backend/api/models/${name.singular}.js`, model.createModel(capitalize(name.singular), data), () => {
      createFile(`./backend/api/controllers/${name.singular}.js`, controller.createController({singular: capitalize(name.singular), plural: name.plural}, data.data), () => {
        createFile(`./backend/api/routes/${name.singular}.js`, route.createRoute({singular: capitalize(name.singular), plural: name.plural}, auth), () => {
          const app = require('../../app');
          mountEndpoints(name.singular, app);
        });
      });
    });
};

Here I basically pass along the data from the POST method to the model, controller & route file which are created asynchronously. When all files are created I mount the endpoint route to the app. The logic to mount the route is:

const mountEndpoints = (path, app) => {
  const module = require(`../routes/${path}`);
  app.use(`/api/${module.plural ? `${module.plural}` : `${path}s`}`, module);
}

A created route might look like the following:

const express   = require('express');
const router    = express.Router();
const checkAuth = require('../middleware/check-auth');

const ProductController = require('../controllers/product');

router.route('/')
    .get(ProductController.getAll)
    .post(checkAuth, ProductController.createOne);

router.route('/:id')
    .get(ProductController.getOne)
    .patch(checkAuth, ProductController.patchOne)
    .delete(checkAuth, ProductController.deleteOne);

module.exports = router;
module.exports.plural = 'products';

checkAuth includes some logic for authorization/authentication.

The code does pretty much what I want it to do except that I don't know how to handle the positioning of the route before the error handling.

user_1318694 · Answer

Express routes will be handled in creation order.

To add routes in specific locations after the app definition you can create a placeholder router and attach routes to there instead of the app itself.

Express doesn't support deleting routes once they are defined, but you can replace an entire router.

Create an express router instance (or even another app if needed) to mount the dynamic endpoints on. Redefine the router whenever you want to change the routes (apart from additions to the end of the routers stack, which is supported by express).

// Routes
app.use('/api/products', productRoutes);
app.use('/api/users', userRoutes);

let dynamicApiRouter = null

export function setupDynamicRouter(config) {
  dynamicApiRouter = new express.Router()
  // Add routes to dynamicApiRouter from `config`
  dynamicApiRouter[config.method](config.path, config.handler)
}

app.use('/api', (req, res, next) => dynamicApiRouter(req, res, next))

// Error handling
app.use((req, res, next) => {
    const err = new Error('Not found');
    err.status = 404;
    next(err);
});

app.use((err, req, res, next) => {
    res.status(err.status || 500).json({error: {message: err.message}});
});

Then when you mount a new endpoint, pass the router in and remove the /api path prefix as that's now handled outside the router in the parent app.

const mountEndpoints = (path, router) => {
  const module = require(`../routes/${path}`);
  router.use(`/${module.plural ? `${module.plural}` : `${path}s`}`, module);
}

user_1260020 · Answer

Just adding to the above answer, which is correct, you basically need either an express app or a Router instance to attach your routes to.

In my case I had a legacy Node.js app that was initialized asynchronously, meaning that the underlying express middleware was returned after the database connection was initialized internally.

Here myApp is the legacy app that have an init method with a callback that returns the express middleware instance after some time:

var express = require('express')
var myApp = require('my-app')

module.exports = (config) => {
  // create an app handle
  var handle = express()

  myApp.init(config, (err, instance) => {
    if (err) {}
    // mount lazily
    handle.use(instance)
  })

  // return immediately
  return handle
}

I called that wrapper module lazy-load.js and then I use it like this:

var express = require('express')
var lazyLoad = require('lazy-load')

express()
  .use('/a', lazyLoad(require('./config-a.json')))
  .use('/b', lazyLoad(require('./config-b.json')))
  .listen(3000)

I wanted to serve multiple instances of the same app but with different configuration for the different users.

As for the original question, again, as long as you keep reference to your handle middleware instance, initially attached to your server, you can keep adding new routes to it at runtime.

ExpressJS: Adding routes dynamically at runtime

2 Answers