webpack hmr + socketio "user connected" spam when initialize

Question

I'm trying socketio with webpack dev server using hmr. I'm not sure if it's related to my problem.

This is the most simple example I use:

Server side:

this.io.on('connection', function(socket){
   console.log('a user connected');
});

Client side (inside a react component):

componentDidMount() {
    var socket = io();
}

The problem when I do that it's "a user connected" appears a lot on the server side like if io() function is constantly called. It's spamming io connection.

Any idea where does this come from ? related to hmr or webpack ?

Edit: I've try to initialize socketIO own server Server side:

var server = app.listen(process.env.PORT || 3000 , function() {
        var host = server.address().address;
        var port = server.address().port;
        console.log('App listening at http://%s:%s', host, port);
    });
    var ioServer = http.listen(process.env.PORT || 9090 , function() {
        var host = ioServer.address().address;
        var port = ioServer.address().port;
        console.log('IO listening at http://%s:%s', host, port);
    });

Client side:

var socket = io.connect('http://127.0.0.1:9090');

But it's the same result "a user connected" heavy spam. Hundreds of connection to io.