server.js

const express = require('express');
const app = express();
const http = require('http');
const {Server} = require('socket.io');
const ACTIONS = require('./src/Actions');

const server = http.createServer(app);
const io = new Server(server);

const userSocketMap = {};
function getAllConnectedClients(roomId) {
    return Array.from(io.sockets.adapter.rooms.get(roomId) || []).map(
        (socketId) => {
            return {
                socketId,
                username: userSocketMap[socketId],
            };
        }
    );
}


io.on('connection', (socket) => {
    console.log('socket connected', socket.id);
    
    socket.on(ACTIONS.JOIN, ({roomId, username}) => {
        userSocketMap[socket.id] = username;
        socket.join(roomId);
        const clients = getAllConnectedClients(roomId);
        clients.forEach(({socketId}) => {
            io.to(socketId).emit(ACTIONS.JOINED, {
                clients,
                username,
                socketId: socket.id,
            });
        });
    });

    socket.on(ACTIONS.CODE_CHANGE, ({roomId, code}) => {
        // console.log('receiving', code);  //Comment: To check whether server is receiving the code or not...
        socket.in(roomId).emit(ACTIONS.CODE_CHANGE, {code});
    });

    socket.on(ACTIONS.SYNC_CODE, ({socketId, code}) => {
        io.to(socketId).emit(ACTIONS.CODE_CHANGE, {code});
    })

    socket.on('disconnecting', () => {
        const rooms = [...socket.rooms];
        rooms.forEach((roomId) => {
            socket.in(roomId).emit(ACTIONS.DISCONNECTED, {
                socketId: socket.id,
                username: userSocketMap[socket.id],
            });
        });
        delete userSocketMap[socket.id];
        socket.leave();
    });
});

const PORT = process.env.PORT || 5000;
server.listen(PORT, () => console.log(`Listening on port ${PORT}`));