start.js

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

//routes.js
module.exports = function (app) {
    app.get("/", require("./models/index"));
    app.get("/foo", require("./models/foo"));
    app.get("/bar", require("./models/bar"));
}

//models/index.js
module.exports = function(req, res) {
    res.end("Index");
};

//models/foo.js
module.exports = function(req, res) {
    res.end("Foo");
};

//models/bar.js
module.exports = function(req, res) {
    res.end("Bar");
};