sg/index.js

const express = require('express');
var app  = express()
var http = require('http').Server(app);
var io = require('socket.io')(http);

app.use(express.static('public'))

let gamers = []

let cleanSocket =  gamer => {
    let copy = {...gamer}
    delete copy.socket
    return copy
}

let emitGamers = () => io.emit('gamers', gamers.map(cleanSocket))

let thisGamer = s  => gamers.filter(g => g.socket === s) [0]
let gamerById = id => gamers.filter(g => g.id     === id)[0]

io.on('connection', socket => {
    socket.emit('hi', {id: socket.id})
    socket.on('disconnect', () => {
        gamers = gamers.filter(n => n.socket !== socket)
        emitGamers()
    });

    socket.on('conn', msg => {
        gamers.push({nick: msg.nick, socket: socket, id: socket.id})
        emitGamers()
    })

    socket.on('newGame', msg => {
        let gamer = thisGamer(socket)
        gamer.newGame = msg.newGame
        emitGamers()
    })

    socket.on('startGame', ({id}) => {
        let gamer = thisGamer(socket)
        let enemy = gamerById(id)
        //console.log(id, gamers)
        if (enemy && enemy.newGame){
            gamer.inGameWith = enemy.id
            enemy.inGameWith = gamer.id

            gamer.turn  = Math.random() > 0.5
            enemy.turn  = !gamer.turn
        }
        gamer.socket.emit('startGame', cleanSocket(gamer))
        enemy.socket.emit('startGame', cleanSocket(enemy))

        if (gamer.turn) gamer.socket.emit('turn')
        else enemy.socket.emit('turn')

        emitGamers()
    })

    socket.on('turn', data => {
        let gamer = thisGamer(socket)
        let enemy = gamerById(gamer.inGameWith)
        if (gamer && enemy && 
            gamer.inGameWith === enemy.id && 
            enemy.inGameWith === gamer.id &&
            gamer.turn){

            gamer.turn = !gamer.turn
            enemy.turn = !enemy.turn
            enemy.socket.emit('turn', data)
        }
    })
});

http.listen(4000, function(){
      console.log(`listening`);
});