Express and WebSocket listening on the same port

I have an app.js which is used to trigger two events when some POST data are received:

1. Insert POST data into a database
2. Send a message to a client using a WebSocket

Here is the app.js (only the important lines)

var express = require('express');
var bodyParser = require('body-parser');
var server = require('./server');

var app = express();
var port = process.env.PORT || 3000;

app.post('/server', server);

app.listen(port, function(){
  console.log('Slack bot listening');
});

And here is the server.js (only the important lines)

var db = require('./DB');
var WebSocketServer = require('ws').Server;

var insertData = function(req, res){

    var wss = new WebSocketServer({server: server});
    console.log('WebSocketServer created');
    wss.on('connection', function(wss){
        wss.send(JSON.stringify('Socket open'));
    });
    wss.on('close', function(){
        console.log('WebServerSocket has been closed');
    });
};

module.exports = insertData;

What I would like to achieve is to set the WebSocketServer in a way that it listen to the same port of the app. I thought about passing the server var from app.js to server.js but

1. I think this a not an elegant way to do it
2. I don't know how to do it

What do you guys think?

from Express and WebSocket listening on the same port