How to use Installing

npm install socket.io

Using with Node HTTP server

For this example, simply run npm install socket.io Server (app.js)

var app = require(‘http’).createServer(handler) , io = require(‘socket.io’).listen(app) , fs = require(‘fs’)

app.listen(80);

function handler (req, res) { fs.readFile(__dirname + ‘/index.html’, function (err, data) { if (err) { res.writeHead(500); return res.end(‘Error loading index.html’); }

res.writeHead(200);
res.end(data);

}); }

io.sockets.on(‘connection’, function (socket) { socket.emit(‘news’, { hello: ‘world’ }); socket.on(‘my other event’, function (data) { console.log(data); }); });

Client (index.html)

<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>

Using with the Express 3 web framework

Express 3 requires that you instantiate a http.Server to attach socket.io to first: Server (app.js)

var app = require(‘express’)() , server = require(‘http’).createServer(app) , io = require(‘socket.io’).listen(server);

server.listen(80);

app.get(’/’, function (req, res) { res.sendfile(__dirname + ‘/index.html’); });

io.sockets.on(‘connection’, function (socket) { socket.emit(‘news’, { hello: ‘world’ }); socket.on(‘my other event’, function (data) { console.log(data); }); });

Client (index.html)

<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>

Using with the Express web framework

You can serve normal pages and AJAX requests with Express, and attach your socket.io server

For this example, simply run npm install socket.io express Server (app.js)

var app = require(‘express’).createServer() , io = require(‘socket.io’).listen(app);

app.listen(80);

app.get(’/’, function (req, res) { res.sendfile(__dirname + ‘/index.html’); });

io.sockets.on(‘connection’, function (socket) { socket.emit(‘news’, { hello: ‘world’ }); socket.on(‘my other event’, function (data) { console.log(data); }); });

Client (index.html)

<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>

Sending and receiving events.

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

// 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

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

<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>

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. Server

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

<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

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); }); });

Sending and getting data (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

var io = require(‘socket.io’).listen(80);

io.sockets.on(‘connection’, function (socket) { socket.on(‘ferret’, function (name, fn) { fn(‘woot’); }); });

Client

<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

var io = require(‘socket.io’).listen(80);

io.sockets.on(‘connection’, function (socket) { socket.broadcast.emit(‘user connected’); });

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

var io = require(‘socket.io’).listen(80);

io.sockets.on(‘connection’, function (socket) { socket.on(‘message’, function () { }); socket.on(‘disconnect’, function () { }); });

Client

<script> var socket = io.connect(‘http://localhost/’); socket.on(‘connect’, function () { socket.send(‘hi’);

socket.on('message', function (msg) {
  // my msg
});

}); </script>