How to use socket.io with an Express server

Question

If I define my*Express* server like this:

```javascript
const app    = require('express')();
const server = app.listen(3000);
const io     = require('socket.io');
const http   = require('http');
```
How can I use*socket.io* so that I can do`io.on('connection', …)`?

Accepted Answer

`io = io(http.Server(app));`

Accepted Answer

`io = io(server);`

Answer

`io = io(app);`

Answer

`io = io(http.createServer(server));`

Question from the Node.js test

How to use socket.io with an Express server