NodeJS Cannot find module 'io' ( socket.io with express 4.15.3)

Question

I am new in NodeJS. I am trying to run simple chat application with express and socket.io module, but when I run application, on the page where I am using socket, on console I am getting this error, and can't understand the problem. on web page I am getting this (see attached image)

Error: Cannot find module 'io'
    at Function.Module._resolveFilename (module.js:469:15)
    at Function.Module._load (module.js:417:25)
    at Module.require (module.js:497:17)
    at require (internal/module.js:20:19)
    at new View (/Applications/XAMPP/xamppfiles/htdocs/NODE/express/node_modules/express/lib/view.js:80:30)

Actually I have found this example in internet ( https://github.com/socketio/socket.io/tree/master/examples/chat ), and try to join it to my project.For view I am using EJS. All my JS and css files in public directory, I have copied socket.io.js from node_modules/socket.io-client/dist/socket.io.js to my javascript directory. Here is my code.

app.js

let express = require('express');
let bodyParser = require('body-parser');
let path = require('path');
let expressValidator = require('express-validator');
let db = require('mysql');
let sessions = require('express-session');

let session;

let app = express();

let connection = db.createConnection({
    host:"localhost",
    user:'root',
    password:'',
    database:'oulala'
});

connection.connect((error)=>{
    if(error){
        console.log('Error')
    }else{
        console.log("connected");
    }
});

//Body parser Middleware
app.use(bodyParser.json());
app.use(bodyParser.urlencoded({extended:true}));
app.use(sessions({
    secret:'$%2878asd8783yuh3b129x831726375r367*&^%$#',
    resave:false,
    saveUninitialized:true
}))

//View engine
app.set('view engine','ejs');
app.set('views',path.join(__dirname,'views'));

app.use(express.static(__dirname + '/public'));

//Global Vars

app.use((req,res,next)=>{
    res.locals.errors = null;
    res.locals.isAuthenticated = false;
    next();
});

app.use(expressValidator({
    errorFormatter: (param,msg,value)=>{
        let namespace = param.split('.')
        , root = namespace.shift()
        , formParam = root;

        while(namespace.length){
            formParam+= '['+namespace.shift()+']';
        }
        return {
            param : formParam,
            msg   : msg,
            value : value
        }

    }
}));

app.get('/logout',(req,res)=>{
    req.session.destroy((error)=>{
        res.redirect('/');
    })
})

app.post('/login',(req,res) => {
    session = req.session;
    req.checkBody('username','Username is required').notEmpty();
    req.checkBody('password','Password is required').notEmpty();
    errors = req.validationErrors();
    if ( errors ) {
        res.render('login',{
            title:"Login",
            errors:errors
        });
    }else{
        if(req.body.username == 'admin' && req.body.password == 'admin'){
            session.uniqueID = req.body.username;
            isAuthenticated = true;
        }
        res.redirect('/');
    }
})


app.get('/:page?',(req,res) => {
    //res.send('Hello first page');
    //res.json(people);

    let page = req.params.page;
    if ( page ) {
        if ( page == 'posts' ){
            connection.query("SELECT * FROM members",(error,rows,fields)=>{
                if(error){
                    connection.release();
                    console.log('Error in the query - '+error);

                }else{
                    res.render(page,{
                        title:page,
                        users:rows
                    });
                }
            });

        }else{
            res.render(page,{
                title:page,
                user:authenticate
            });
        }

    }else{


        session = req.session;
        if(session.uniqueID){
            res.render('index',{
                title:"Index",
                user:authenticate
            });
        }else{
            res.render('login',{
                title:"Login",
                user:authenticate
            });
        }
    }

});

// get form submition, post request
app.post('/users/add',(req,res) => {
    //console.log(req.body.first_name); // req.body - request object

    req.checkBody('first_name','Fisrtname is required').notEmpty();
    req.checkBody('last_name','Lastname is required').notEmpty();
    req.checkBody('email','Email is required').notEmpty();
    errors = req.validationErrors();

    if ( errors ) {
        res.render('index',{
            title:"Customers",
            users:people,
            errors:errors
        });
    }else{
        var newUser = {
            first_name:req.body.first_name,
            last_name:req.body.last_name,
            email:req.body.email
        }

        people.push(newUser);

        res.render(page,{
            title:page,
            users:people,
            user:authenticate
        });
    }

});

app.listen(3000, () => {
    console.log('server started on port 3000....');
});

var server = require('http').createServer(app);
var io = require('socket.io')(server);

// Chatroom

var numUsers = 0;

io.on('connection', function (socket) {
  var addedUser = false;

  // when the client emits 'new message', this listens and executes
  socket.on('new message', function (data) {
    // we tell the client to execute 'new message'
    socket.broadcast.emit('new message', {
      username: socket.username,
      message: data
    });
  });

  // when the client emits 'add user', this listens and executes
  socket.on('add user', function (username) {
    if (addedUser) return;

    // we store the username in the socket session for this client
    socket.username = username;
    ++numUsers;
    addedUser = true;
    socket.emit('login', {
      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', function () {
    socket.broadcast.emit('typing', {
      username: socket.username
    });
  });

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

  // when the user disconnects.. perform this
  socket.on('disconnect', function () {
    if (addedUser) {
      --numUsers;

      // echo globally that this client has left
      socket.broadcast.emit('user left', {
        username: socket.username,
        numUsers: numUsers
      });
    }
  });
});

---

client.js

$(function() {
  var FADE_TIME = 150; // ms
  var TYPING_TIMER_LENGTH = 400; // ms
  var COLORS = [
    '#e21400', '#91580f', '#f8a700', '#f78b00',
    '#58dc00', '#287b00', '#a8f07a', '#4ae8c4',
    '#3b88eb', '#3824aa', '#a700ff', '#d300e7'
  ];

  // Initialize variables
  var $window = $(window);
  var $usernameInput = $('.usernameInput'); // Input for username
  var $messages = $('.messages'); // Messages area
  var $inputMessage = $('.inputMessage'); // Input message input box

  var $loginPage = $('.login.page'); // The login page
  var $chatPage = $('.chat.page'); // The chatroom page

  // Prompt for setting a username
  var username;
  var connected = false;
  var typing = false;
  var lastTypingTime;
  var $currentInput = $usernameInput.focus();

  var socket = io();

  function addParticipantsMessage (data) {
    var message = '';
    if (data.numUsers === 1) {
      message += "there's 1 participant";
    } else {
      message += "there are " + data.numUsers + " participants";
    }
    log(message);
  }

  // Sets the client's username
  function setUsername () {
    username = cleanInput($usernameInput.val().trim());

    // If the username is valid
    if (username) {
      $loginPage.fadeOut();
      $chatPage.show();
      $loginPage.off('click');
      $currentInput = $inputMessage.focus();

      // Tell the server your username
      socket.emit('add user', username);
    }
  }

  // Sends a chat message
  function sendMessage () {
    var message = $inputMessage.val();
    // Prevent markup from being injected into the message
    message = cleanInput(message);
    // if there is a non-empty message and a socket connection
    if (message && connected) {
      $inputMessage.val('');
      addChatMessage({
        username: username,
        message: message
      });
      // tell server to execute 'new message' and send along one parameter
      socket.emit('new message', message);
    }
  }

  // Log a message
  function log (message, options) {
    var $el = $('<li>').addClass('log').text(message);
    addMessageElement($el, options);
  }

  // Adds the visual chat message to the message list
  function addChatMessage (data, options) {
    // Don't fade the message in if there is an 'X was typing'
    var $typingMessages = getTypingMessages(data);
    options = options || {};
    if ($typingMessages.length !== 0) {
      options.fade = false;
      $typingMessages.remove();
    }

    var $usernameDiv = $('<span class="username"/>')
      .text(data.username)
      .css('color', getUsernameColor(data.username));
    var $messageBodyDiv = $('<span class="messageBody">')
      .text(data.message);

    var typingClass = data.typing ? 'typing' : '';
    var $messageDiv = $('<li class="message"/>')
      .data('username', data.username)
      .addClass(typingClass)
      .append($usernameDiv, $messageBodyDiv);

    addMessageElement($messageDiv, options);
  }

  // Adds the visual chat typing message
  function addChatTyping (data) {
    data.typing = true;
    data.message = 'is typing';
    addChatMessage(data);
  }

  // Removes the visual chat typing message
  function removeChatTyping (data) {
    getTypingMessages(data).fadeOut(function () {
      $(this).remove();
    });
  }

  // Adds a message element to the messages and scrolls to the bottom
  // el - The element to add as a message
  // options.fade - If the element should fade-in (default = true)
  // options.prepend - If the element should prepend
  //   all other messages (default = false)
  function addMessageElement (el, options) {
    var $el = $(el);

    // Setup default options
    if (!options) {
      options = {};
    }
    if (typeof options.fade === 'undefined') {
      options.fade = true;
    }
    if (typeof options.prepend === 'undefined') {
      options.prepend = false;
    }

    // Apply options
    if (options.fade) {
      $el.hide().fadeIn(FADE_TIME);
    }
    if (options.prepend) {
      $messages.prepend($el);
    } else {
      $messages.append($el);
    }
    $messages[0].scrollTop = $messages[0].scrollHeight;
  }

  // Prevents input from having injected markup
  function cleanInput (input) {
    return $('<div/>').text(input).text();
  }

  // Updates the typing event
  function updateTyping () {
    if (connected) {
      if (!typing) {
        typing = true;
        socket.emit('typing');
      }
      lastTypingTime = (new Date()).getTime();

      setTimeout(function () {
        var typingTimer = (new Date()).getTime();
        var timeDiff = typingTimer - lastTypingTime;
        if (timeDiff >= TYPING_TIMER_LENGTH && typing) {
          socket.emit('stop typing');
          typing = false;
        }
      }, TYPING_TIMER_LENGTH);
    }
  }

  // Gets the 'X is typing' messages of a user
  function getTypingMessages (data) {
    return $('.typing.message').filter(function (i) {
      return $(this).data('username') === data.username;
    });
  }

  // Gets the color of a username through our hash function
  function getUsernameColor (username) {
    // Compute hash code
    var hash = 7;
    for (var i = 0; i < username.length; i++) {
       hash = username.charCodeAt(i) + (hash << 5) - hash;
    }
    // Calculate color
    var index = Math.abs(hash % COLORS.length);
    return COLORS[index];
  }

  // Keyboard events

  $window.keydown(function (event) {
    // Auto-focus the current input when a key is typed
    if (!(event.ctrlKey || event.metaKey || event.altKey)) {
      $currentInput.focus();
    }
    // When the client hits ENTER on their keyboard
    if (event.which === 13) {
      if (username) {
        sendMessage();
        socket.emit('stop typing');
        typing = false;
      } else {
        setUsername();
      }
    }
  });

  $inputMessage.on('input', function() {
    updateTyping();
  });

  // Click events

  // Focus input when clicking anywhere on login page
  $loginPage.click(function () {
    $currentInput.focus();
  });

  // Focus input when clicking on the message input's border
  $inputMessage.click(function () {
    $inputMessage.focus();
  });

  // Socket events

  // Whenever the server emits 'login', log the login message
  socket.on('login', function (data) {
    connected = true;
    // Display the welcome message
    var message = "Welcome to Socket.IO Chat – ";
    log(message, {
      prepend: true
    });
    addParticipantsMessage(data);
  });

  // Whenever the server emits 'new message', update the chat body
  socket.on('new message', function (data) {
    addChatMessage(data);
  });

  // Whenever the server emits 'user joined', log it in the chat body
  socket.on('user joined', function (data) {
    log(data.username + ' joined');
    addParticipantsMessage(data);
  });

  // Whenever the server emits 'user left', log it in the chat body
  socket.on('user left', function (data) {
    log(data.username + ' left');
    addParticipantsMessage(data);
    removeChatTyping(data);
  });

  // Whenever the server emits 'typing', show the typing message
  socket.on('typing', function (data) {
    addChatTyping(data);
  });

  // Whenever the server emits 'stop typing', kill the typing message
  socket.on('stop typing', function (data) {
    removeChatTyping(data);
  });

  socket.on('disconnect', function () {
    log('you have been disconnected');
  });

  socket.on('reconnect', function () {
    log('you have been reconnected');
    if (username) {
      socket.emit('add user', username);
    }
  });

  socket.on('reconnect_error', function () {
    log('attempt to reconnect has failed');
  });

});

---

index.ejs

<% include partials/header %>
    <h1><%= title %></h1>
    <ul class="pages">
    <li class="chat page">
      <div class="chatArea">
        <ul class="messages"></ul>
      </div>
      <input class="inputMessage" placeholder="Type here..."/>
    </li>
    <li class="login page">
      <div class="form">
        <h3 class="title">What's your nickname?</h3>
        <input class="usernameInput" type="text" maxlength="14" />
      </div>
    </li>
  </ul>
    <script src="https://code.jquery.com/jquery-1.10.2.min.js"></script>
    <script src="/javascript/socket.io.js"></script>
    <script src="/javascript/client.js"></script>
<% include partials/footer %>

---

package.json

{
  "name": "customerapp",
  "version": "1.0.0",
  "description": "Simple customer managment app",
  "main": "app.js",
  "scripts": {
    "test": "echo \"Error: no test specified\" && exit 1"
  },
  "author": "Anna Gabrielyan",
  "license": "ISC",
  "dependencies": {
    "body-parser": "^1.17.2",
    "ejs": "^2.5.6",
    "express": "^4.15.3",
    "express-session": "^1.15.3",
    "express-validator": "^3.2.0",
    "mysql": "^3.10.10",
    "oauth2-server": "^2.4.1",
    "socket.io": "^2.0.2"
  }
}

Answer 1

First you need to install packages using below command

npm install

This command will install all the packages from your package.json once done you can run this program.

Answer 2

did you install socket.io using npm. if not try

npm install --save socket.io

can you show me package.json,?

Answer 3

I find my bug. I removed this code

app.listen(3000, () => {
    console.log('server started on port 3000....');
});

and added this

server.listen(3000);

after this

var server = require('http').createServer(app);
var io = require('socket.io').listen(server);

thanks to @Curious for helping and great answer socket.io - can't get it to work, having 404's on some kind of polling call