Socket.IO

// package.json
{
  "name": "socket-chat-example",
  "version": "0.0.1",
  "description": "my first socket.io app",
  "dependencies": {}
}

$ npm install --save express
$ npm install --save socket.io

// index.js
var app = require('express')();    // import class (node_modules)
var http = require('http').Server(app);
var io = require('socket.io')(http);

app.get('/', function(req, res){  // localhost:3000/
  res.sendfile('index.html');
});


app.get('/link', function(req, res){  // localhost:3000/link
  res.sendfile('link.html');
});

io.on('connection', function(socket){  // connected to client
  socket.on('chat message', function(msg){  // receiving 'message' from client
  io.emit('chat message', msg);  // sending 'message' to client
  });
});

http.listen(3000, function(){  // port
  console.log('listening on *:3000');
});

//index.html
<!doctype html>
<html>
  <head>
    <title>Socket.IO chat</title>

    <script src="/socket.io/socket.io.js"></script>
    <script src="http://code.jquery.com/jquery-1.11.1.js"></script>

  </head>

  <body>

    <ul id="messages"></ul>

    <form action="">
      <input id="m" />
      <button>Send</button>
    </form>

    <a href="link"> Link </a>

    <script>
      var socket = io();  // io('127.0.0.1');

      $('form').submit(function(){
        socket.emit('chat message', $('#m').val());  // sending message to server
        $('#m').val('');
        return false;  // Stopping the submit
      });

      socket.on('chat message', function(msg){  // receiving message from server
        $('#messages').append($('<li>').text(msg));
      });

    </script>

  </body>
</html>