Example of how a main express app can mount sub-applications on a mount point with app.use('/mount-point', subapp); If you GET /, you'll see the main_app's '/' response. If you GET /ep_app, you'll see the ep_app's '/' response.

ep_app.js

const express = require("express");
const router = express.Router();

router.get('/', function (req, res) {
  res.send("This is the '/' route in ep_app");
});

module.exports = router;

main_app.js

#!/usr/bin/env node
const express = require("express");
const http = require("http");

const mainRouter = express.Router();
const epRouter = require("./ep_app");
const server = express();

mainRouter.get('/', function (req, res) {
  res.send("This is the '/' route in main_app");
});

server.use('/ep_app', epRouter);
server.use('/', mainRouter);

http.createServer(server).listen(3000);

I was looking for a perfect example of subapp and you're the savior! thank you!

Are there negative (memory?) implications of building apps like this v. using a Router?

This should use a Router() app, not an express() server.

The difference is that certain security parameters (such as trust proxy) and other global state will not propagate properly if a new server is created.

Also, this should use http as the server for a similar reason - the express server conflicts with global state of the http server.

app.js:

'use strict';

var express = require("express");
var app = express.Router();

app.get('/', function (req, res) {
  res.json({ message: "This is the '/' route in ep_app" });
});

module.exports = app;

server.js:

#!/usr/bin/env node
'use strict';

var http = require('http');
var express = require("express");
var server = express();
var app = express.Router();
var epApp = require("./app.js");

app.get('/', function (req, res) {
  res.send("This is the '/' route in main_app");
});

server.use('/ep_app', epApp);
server.use('/', app);

http.createServer(server).listen(3000);

Why do so many people skip these steps and try to squish everything together? Documentation code golf.

@coolaj86 I updated the gist to incorporate your tips. Thanks! Check back in another 9 years for further tweaks LOL.