Node + Express application Problem with module creation

A possible solution is the following:

1. You take the code between the two double lines and copy it into another module. With the particularity that you put it inside a function that receives the server as an argument.
2. You make the module expose that function.
3. You import the module in the script that creates the server and use the function to configure SocketIO

The new module with the code for socket io would look like this:

const socketIO = require('socket.io');

module.exports = function(server){
  const io = socketIO(server);

  var onlineUsers = [];

  io.on('connection', (socket)=> {

    let query = socket.handshake.query;
    let token = query.token;
    let usu = {
      'id': socket.id,
      'codigo': query.usuCodigo,
      'nome': query.usuNome
    }
    onlineUsers.push(usu);
    io.emit('onlineUsers', { type:'onlineUsers', 'usuarios': onlineUsers });

    socket.on('disconnect', ()=> {

      onlineUsers.splice(onlineUsers.indexOf(socket.id), 1);
      let usu = JSON.stringify(onlineUsers);
      io.emit('onlineUsers', { type:'onlineUsers', 'usuarios': usu });
    });

    socket.on('onlineUsers', () => {
      let usu = onlineUsers;
      io.emit('onlineUsers', { type:'onlineUsers', 'usuarios': usu });
    });

    socket.on('add-message', (message) => {
      let mx = JSON.parse(message);
      mx.data = new(Date);
      io.emit('message', { type:'new-message', 'mensaxe': mx });
    });

  });
};

Assuming that the new module is named setup-socket-io.jsand that it is in the same directory as the script used to create the server, the latter once modified is as follows:

const express = require('express');
const path = require('path');
const http = require('http');
const cfg = require('./config/config')
const middleware = require('./middleware');
const setupSocketIO = require('./setup-socket-io');

const app = express();

middleware.useMiddleware(app);

// Configuración de rutas
require('./api/index')(app);

const options = {
        extensions: ['htm', 'html'],
        maxAge: '1d',
        setHeaders: res => res.set('x-timestamp', Date.now())
    }
app.use(express.static(path.join(__dirname, '/dist'), options));
app.use(express.static(path.join(__dirname, '/dist/assets'), options));

const server = http.createServer(app);

console.log("==============================================");
setupSocketIO(server);
console.log("==============================================");

const porto = cfg.PORTO;
server.listen(porto, ()=> {
  console.log(`Servidor correndo no oo ${porto}`);
})