Ubuntu 16.04
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Install Node.js
2016/06/15
 
Install ServerSide JavaScript Environment "Node.js".
[1] Install Node.js 4.x (LTS).
root@www:~#
curl -O https://deb.nodesource.com/setup_4.x

root@www:~#
sh setup_4.x

root@www:~#
apt-get -y install nodejs
root@www:~#
node -v

v4.4.5
[2] Create a test tool. It's possible to do it as a common user.
ubuntu@www:~$
vi helloworld.js 
var http = require('http');
http.createServer(function (req, res) {
  res.writeHead(200, {'Content-Type': 'text/plain'});
  res.end('Hello World\n');
}).listen(1337, '127.0.0.1');
console.log('listening on http://127.0.0.1:1337/');
# run server

ubuntu@www:~$
node helloworld.js &
# verify (it's OK if following reply is back )

ubuntu@www:~$
curl http://127.0.0.1:1337/

Hello World
[3] Install Socket.IO and create a test apprication with using WebSocket.
ubuntu@www:~$
npm install socket.io express
ubuntu@www:~$
vi chat.js 
var app = require('express')();
var http = require('http').Server(app);
var io = require('socket.io')(http);

app.get('/', function(req, res){
  res.sendFile(__dirname + '/index.html');
});

io.on('connection', function(socket){
  socket.on('chat message', function(msg){
    io.emit('chat message', msg);
  });
});

http.listen(1337, function(){
  console.log('listening on *:1337');
});
ubuntu@www:~$
vi index.html 
<!DOCTYPE html>
<html>
<head>
<title>WebSocket Chat</title>
</head>
<body>
<form action="">
<input id="sendmsg" autocomplete="off" /><button>Send</button>
</form>
<ul id="messages" style="list-style-type: decimal; font-size: 16px; font-family: Arial;"></ul>
<script src="/socket.io/socket.io.js"></script>
<script src="http://code.jquery.com/jquery.min.js"></script>
<script>
  var socket = io();
  $('form').submit(function(){
    socket.emit('chat message', $('#sendmsg').val());
    $('#sendmsg').val('');
    return false;
  });
  socket.on('chat message', function(msg){
    $('#messages').append($('<li style="margin-bottom: 5px;">').text(msg));
  });
</script>
</body>
</html>
ubuntu@www:~$
node chat.js

listening on *:1337
  Access to "http://(server's hostname or IP address):1337/" from a Client computer to make sure sample app works normally.
 
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