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.
npm install socket.ioFirst, 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:
var app = express.createServer()
, io = io.listen(app);
app.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.
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');
});
});Sometimes it's necessary to store data associated with a client that's necessary for the duration of the session.
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);
});
});
});<script>
var socket = io.connect('http://localhost');
socket.on('connect', function () {
socket.emit('set nickname', confirm('What is your nickname?'));
socket.on('ready', function () {
console.log('Connected !');
socket.emit('msg', confirm('What is your message?'));
});
});
</script>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':
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' });
});<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>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.
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);
});
});In the client side, messages are received the same way whether they're volatile or not.
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:
var io = require('socket.io').listen(80);
io.sockets.on('connection', function (socket) {
socket.on('ferret', function (name, fn) {
fn('woot');
});
});<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>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.
var io = require('socket.io').listen(80);
io.sockets.on('connection', function (socket) {
socket.broadcast.emit('user connected');
socket.broadcast.json.send({ a: 'message' });
});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.
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');
});If you just want the WebSocket semantics, you can do that too.
Simply leverage send and listen on the message event:
var io = require('socket.io').listen(80);
io.sockets.on('connection', function (socket) {
socket.on('message', function () { });
socket.on('disconnect', function () { });
});<script>
var socket = io.connect('http://localhost/');
socket.on('connect', function () {
socket.send('hi');
socket.on('message', function (msg) {
// my msg
});
});
</script>Configuration in socket.io is TJ-style:
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');
});