Instead of bogging down your main app.js file with every single route, try and organize it with the Express Routing mindset as stated in their Docs.

A router is an isolated instance of middleware and routes. Routers can be thought of as "mini" applications only capable of performing middleware and routing. Every express application has a built in app router.

So let's pretend you have a setup like so:

your-express-project/
    client/
    server/
        app.js
        *other files and directories**

In your main file (usually server/app.js) get rid of anything route related. Make the following directories and file in your root server directory:

your-express-project/
    client/
    server/
        router/
            routes/
                signup.js
            index.js
        app.js
        *other files and directories*

In your app.js file, just before the module.exports = app; portion add the following:

// Towards bottom of app.js

/**
  * Router
  */
var router = require('./router')(app);

// Error Handling
app.use(function(err, req, res, next) {
    res.status(err.status || 500);
});

module.exports = app;

And then in your server/router/index.js put the following in:

// server/router/index.js

module.exports = function (app) {
    app.use('/signup', require('./routes/signup'));
};

Now you can turn the /signup route into it's own contained area.

// server/router/routes/signup.js

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

// POST /signup
router.post('/', function (req, res) {
    // handle a post request to this route
});

// GET /signup/info
router.get('/info', function (req, res) {
    // handle a get request to this route
});

// etc...

module.exports = router;

What we did in the above is make it so that our app.js file only pulls in 1 route related file. Our router/index.js file serves as the entry port where we can look and get a nice snapshot of all of our applications routes. Each individual route is housed in it's own file located in the router/routes/ directory.

From now on, everytime you want to add a new route, create a new file for it in router/routes/ and add

app.use('/my-new-route/', require('./routes/my-new-route));

Inside of your router/index.js file.