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

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

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

module.exports = app;

main_app.js

#!/usr/bin/env node
var express = require("express");
var app = express();
var ep_app = require("./ep_app");

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

app.listen(3000);