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Socket.IO is a Node.JS project that makes WebSockets and realtime possible in all browsers. It also enhances WebSockets by providing built-in multiplexing, horizontal scalability, automatic JSON encoding/decoding, and more.

==Установка==
 npm install socket.io

==Использование==

First, require socket.io:

 var io = require('socket.io');

Next, attach it to a HTTP/HTTPS server. If you're using the fantastic express web framework:
 Express 3.x
  var app = express()
   , server = require('http').createServer(app)
   , io = io.listen(server);
 
 server.listen(80);
 
 io.sockets.on('connection', function (socket) {
   socket.emit('news', { hello: 'world' });
   socket.on('my other event', function (data) {
     console.log(data);
   });
 });


Finally, load it from the client side code:
 
 <script src="/socket.io/socket.io.js"></script>
 <script>
   var socket = io.connect('http://localhost');
   socket.on('news', function (data) {
     console.log(data);
     socket.emit('my other event', { my: 'data' });
   });
 </script>
  
 For more thorough examples, look at the examples/ directory.

==Примеры использования==
Sending and receiving events.

Socket.IO allows you to emit and receive custom events. Besides connect, message and disconnect, you can emit custom events:

 // note, io.listen(<port>) will create a http server for you
 var io = require('socket.io').listen(80);
 
 io.sockets.on('connection', function (socket) {
   io.sockets.emit('this', { will: 'be received by everyone' });
 
   socket.on('private message', function (from, msg) {
     console.log('I received a private message by ', from, ' saying ', msg);
   });
 
   socket.on('disconnect', function () {
     io.sockets.emit('user disconnected');
   });
 });

Storing data associated to a client

Sometimes it's necessary to store data associated with a client that's necessary for the duration of the session.

* '''Server side'''

 var io = require('socket.io').listen(80);
 
 io.sockets.on('connection', function (socket) {
   socket.on('set nickname', function (name) {
     socket.set('nickname', name, function () { socket.emit('ready'); });
   });
 
   socket.on('msg', function () {
     socket.get('nickname', function (err, name) {
       console.log('Chat message by ', name);
     });
   });
 });

* '''Client side'''

 <script>
   var socket = io.connect('http://localhost');
 
   socket.on('connect', function () {
     socket.emit('set nickname', prompt('What is your nickname?'));
     socket.on('ready', function () {
       console.log('Connected !');
       socket.emit('msg', prompt('What is your message?'));
     });
   });
 </script>

Restricting yourself to a namespace

If you have control over all the messages and events emitted for a particular application, using the default / namespace works.

If you want to leverage 3rd-party code, or produce code to share with others, socket.io provides a way of namespacing a socket.

This has the benefit of multiplexing a single connection. Instead of socket.io using two WebSocket connections, it'll use one.

The following example defines a socket that listens on '/chat' and one for '/news':

* '''Server side'''

 var io = require('socket.io').listen(80);
 
 var chat = io
   .of('/chat')
   .on('connection', function (socket) {
     socket.emit('a message', { that: 'only', '/chat': 'will get' });
     chat.emit('a message', { everyone: 'in', '/chat': 'will get' });
   });
 
 var news = io
   .of('/news');
   .on('connection', function (socket) {
     socket.emit('item', { news: 'item' });
   });

* '''Client side:'''

 <script>
   var chat = io.connect('http://localhost/chat')
     , news = io.connect('http://localhost/news');
 
   chat.on('connect', function () {
     chat.emit('hi!');
   });
 
   news.on('news', function () {
     news.emit('woot');
   });
 </script>

* Sending volatile messages.

Sometimes certain messages can be dropped. Let's say you have an app that shows realtime tweets for the keyword bieber.

If a certain client is not ready to receive messages (because of network slowness or other issues, or because he's connected through long polling and is in the middle of a request-response cycle), if he doesn't receive ALL the tweets related to bieber your application won't suffer.

In that case, you might want to send those messages as volatile messages.

* '''Server side'''

 var io = require('socket.io').listen(80);
 
 io.sockets.on('connection', function (socket) {
   var tweets = setInterval(function () {
     getBieberTweet(function (tweet) {
       socket.volatile.emit('bieber tweet', tweet);
     });
   }, 100);
 
   socket.on('disconnect', function () {
     clearInterval(tweets);
   });
 });

* '''Client side'''

In the client side, messages are received the same way whether they're volatile or not.

Getting acknowledgements

Sometimes, you might want to get a callback when the client confirmed the message reception.

To do this, simply pass a function as the last parameter of .send or .emit. What's more, when you use .emit, the acknowledgement is done by you, which means you can also pass data along:

* '''Server side'''

 var io = require('socket.io').listen(80);
 
 io.sockets.on('connection', function (socket) {
   socket.on('ferret', function (name, fn) {
     fn('woot');
   });
 });
* '''Client side'''
 
 <script>
   var socket = io.connect(); // TIP: .connect with no args does auto-discovery
   socket.on('connect', function () { // TIP: you can avoid listening on `connect` and listen on events directly too!
     socket.emit('ferret', 'tobi', function (data) {
       console.log(data); // data will be 'woot'
     });
   });
 </script>
* '''Broadcasting messages'''

To broadcast, simply add a broadcast flag to emit and send method calls. Broadcasting means sending a message to everyone else except for the socket that starts it.

* '''Server side'''

 var io = require('socket.io').listen(80);
 
 io.sockets.on('connection', function (socket) {
   socket.broadcast.emit('user connected');
   socket.broadcast.json.send({ a: 'message' });
 });

* '''Rooms'''

Sometimes you want to put certain sockets in the same room, so that it's easy to broadcast to all of them together.

Think of this as built-in channels for sockets. Sockets join and leave rooms in each socket.

* '''Server side'''

 var io = require('socket.io').listen(80);
 
 io.sockets.on('connection', function (socket) {
   socket.join('justin bieber fans');
   socket.broadcast.to('justin bieber fans').emit('new fan');
   io.sockets.in('rammstein fans').emit('new non-fan');
 });
 Using it just as a cross-browser WebSocket

If you just want the WebSocket semantics, you can do that too. Simply leverage send and listen on the message event:

* '''Server side'''

 var io = require('socket.io').listen(80);
 
 io.sockets.on('connection', function (socket) {
   socket.on('message', function () { });
   socket.on('disconnect', function () { });
 });

* '''Client side'''
 
 <script>
   var socket = io.connect('http://localhost/');
   socket.on('connect', function () {
     socket.send('hi');
 
     socket.on('message', function (msg) {
       // my msg
     });
   });
 </script>
Changing configuration

Configuration in socket.io is TJ-style:

* '''Server side'''

 var io = require('socket.io').listen(80);
 
 io.configure(function () {
   io.set('transports', ['websocket', 'flashsocket', 'xhr-polling']);
 });
 
 io.configure('development', function () {
   io.set('transports', ['websocket', 'xhr-polling']);
   io.enable('log');
 });