barebonesSocketBackend.js

let app = require('express')();
let http = require('http').createServer(app);
let io = require('socket.io')(http);

io.on('connection', function(socket) {
    console.log('someone connected!')
    socket.on('chat message', function(msg){
        io.emit('chat message', msg);
    });
});

http.listen(3000, function(){
    console.log('listening on *:3000');
});