index.js

// Setup basic express server
const express = require('express');
const { v4: uuidv4 } = require('uuid');
const app = express();
const path = require('path');
const { Socket } = require('dgram');
const server = require('http').createServer(app);
const io = require('socket.io')(server);
const port = process.env.PORT || 3000;

server.listen(port, () => {
  console.log('Server listening at port %d', port);
});

// Routing
app.use(express.static(path.join(__dirname, 'public')));

// Chatroom

let numUsers = 0;
let users=[];

io.on('connection', (socket) => {
  let addedUser = false;
  // when the client emits 'new message', this listens and executes
  socket.on('new message', (data) => {
    // we tell the client to execute 'new message'
    io.emit('new message', {
      uuid:uuidv4(),
      username: socket.username,
      message: data
    });
  });

  // when the client emits 'add user', this listens and executes
  socket.on('add user', (username) => {
    if (addedUser) return;
    if(users.includes(username)){
    socket.emit('login failed', {
      userName: username
    });
    }
    else{
      users.push(username);
    // we store the username in the socket session for this client
    socket.username = username;
    ++numUsers;
    addedUser = true;
    socket.emit('login', {
      userName: username,
      numUsers: numUsers
    });
    // echo globally (all clients) that a person has connected
    socket.broadcast.emit('user joined', {
      username: socket.username,
      numUsers: numUsers
    });
    }
    
  });

  // when the client emits 'typing', we broadcast it to others
  socket.on('typing', () => {
    socket.broadcast.emit('typing', {
      username: socket.username
    });
  });

  // when the client emits 'stop typing', we broadcast it to others
  socket.on('stop typing', () => {
    socket.broadcast.emit('stop typing', {
      username: socket.username
    });
  });

  // when the user disconnects.. perform this
  socket.on('disconnect', () => {
    if (addedUser) {
      --numUsers;
  
      for( var i = 0; i < users.length; i++){ 
        if ( users[i] === socket.username) { 
          users.splice(i, 1); 
          i--; 
        }
      }
      // echo globally that this client has left
      socket.broadcast.emit('user left', {
        username: socket.username,
        numUsers: numUsers
      });
    }
  });
});