server.js

const path = require('path');
const http = require('http');
const express = require('express');
const socketio = require('socket.io');

//unpairedUser stores socket.id of user
let unpairedUser = null;
const rooms = {};

const app = express();
const server = http.createServer(app);
const io = socketio(server);
app.use(express.static(path.join(__dirname, 'public')));
io.on('connection', (socket) => {
    console.log('a user connected with id = ' + socket.id);
    if (unpairedUser) {
        socket.join(unpairedUser);
        rooms[socket.id] = unpairedUser;
        io.to(unpairedUser).emit('paired');
        unpairedUser = null;
    } else {
        socket.emit('firstPlayer');
        unpairedUser = socket.id;
        socket.join(socket.id);
    }
    socket.on('move', (msg) => {
        socket.broadcast.to(rooms[socket.id] || socket.id).emit('move', msg);
    });
    socket.on('kill', (msg) => {
        socket.broadcast.to(rooms[socket.id] || socket.id).emit('kill', msg);
    });
    socket.on('!multiKill', (msg) => {
        socket.broadcast
            .to(rooms[socket.id] || socket.id)
            .emit('!multiKill', msg);
    });
    socket.on('name', (msg) => {
        socket.broadcast.to(rooms[socket.id] || socket.id).emit('name', msg);
    });
    socket.on('disconnect', () => {
        if (unpairedUser == socket.id) {
            unpairedUser = null;
        }
        socket.broadcast.to(rooms[socket.id] || socket.id).emit('opponentLeft');
    });
});
const PORT = process.env.PORT || 3000;
server.listen(PORT, () => {
    console.log(`Server running on port ${PORT}`);
});