socket.io-client

What is socket.io-client?

The socket.io-client npm package is a client-side library that enables real-time, bidirectional and event-based communication between web clients and servers. It works on every platform, browser or device, focusing equally on reliability and speed.

What are socket.io-client's main functionalities?

Connecting to a server

This code sample demonstrates how to connect to a Socket.IO server running on localhost at port 3000.

const io = require('socket.io-client');
const socket = io('http://localhost:3000');

Emitting events

This code sample shows how to emit an event to the server with an event name and associated data.

socket.emit('event_name', { some: 'data' });

Listening for events

This code sample illustrates how to listen for events emitted by the server and handle them with a callback function.

socket.on('event_name', function(data) {
  console.log(data);
});

Disconnecting from the server

This code sample shows how to handle a disconnection event when the client gets disconnected from the server.

socket.on('disconnect', function() {
  console.log('Disconnected from server');
});

Other packages similar to socket.io-client

ws

The 'ws' package is a simple to use, blazing fast, and thoroughly tested WebSocket client and server implementation. Unlike socket.io-client, which provides an abstraction over WebSocket with additional features like auto-reconnection, 'ws' is a bare WebSocket implementation.

faye-websocket

Faye is a set of tools for simple publish-subscribe messaging between web clients. It's similar to socket.io-client in that it provides an abstraction over WebSocket for real-time communication, but it has a different API and feature set.

sockjs-client

SockJS-client is a browser JavaScript library that provides a WebSocket-like object. SockJS gives you a coherent, cross-browser, Javascript API which creates a low latency, full duplex, cross-domain communication channel between the browser and the web server, with WebSockets or without. It is similar to socket.io-client but focuses more on providing fallback options for environments where WebSocket is not available.

README

socket.io

Sockets for the rest of us

The socket.io client is basically a simple HTTP Socket interface implementation. It looks similar to WebSocket while providing additional features and leveraging other transports when WebSocket is not supported by the user's browser.

var socket = io.connect('http://domain.com');
socket.on('connect', function () {
  // socket connected
});
socket.on('custom event', function () {
  // server emitted a custom event
});
socket.on('disconnect', function () {
  // socket disconnected
});
socket.send('hi there');

Recipes

Utilizing namespaces (ie: multiple sockets)

If you want to namespace all the messages and events emitted to a particular endpoint, simply specify it as part of the connect uri:

var chat = io.connect('http://localhost/chat');
chat.on('connect', function () {
  // chat socket connected
});

var news = io.connect('/news'); // io.connect auto-detects host
news.on('connect', function () {
  // news socket connected
});

Emitting custom events

To ease with the creation of applications, you can emit custom events outside of the global message event.

var socket = io.connect();
socket.emit('server custom event', { my: 'data' });

Forcing disconnection

var socket = io.connect();
socket.on('connect', function () {
  socket.disconnect();
});

Documentation

io#connect

io.connect(uri, [options]);

Options:

• resource

  socket.io

  The resource is what allows the socket.io server to identify incoming connections by socket.io clients. In other words, any HTTP server can implement socket.io and still serve other normal, non-realtime HTTP requests.

• transports

['websocket', 'flashsocket', 'htmlfile', 'xhr-multipart', 'xhr-polling', 'jsonp-polling']

A list of the transports to attempt to utilize (in order of preference).

• 'connect timeout'

5000

The amount of milliseconds a transport has to create a connection before we consider it timed out.

• 'try multiple transports'

true

A boolean indicating if we should try other transports when the connectTimeout occurs.

• reconnect

true

A boolean indicating if we should automatically reconnect if a connection is disconnected.

• 'reconnection delay'

500

The amount of milliseconds before we try to connect to the server again. We are using a exponential back off algorithm for the following reconnections, on each reconnect attempt this value will get multiplied (500 > 1000 > 2000 > 4000 > 8000).

• 'max reconnection attempts'

10

The amount of attempts should we make using the current transport to connect to the server? After this we will do one final attempt, and re-try with all enabled transport methods before we give up.

Properties:

• options

  The passed in options combined with the defaults.

• connected

  Whether the socket is connected or not.

• connecting

  Whether the socket is connecting or not.

• reconnecting

  Whether we are reconnecting or not.

• transport

  The transport instance.

Methods:

• connect(λ)

  Establishes a connection. If λ is supplied as argument, it will be called once the connection is established.

• send(message)

  A string of data to send.

• disconnect

  Closes the connection.

• on(event, λ)

  Adds a listener for the event event.

• once(event, λ)

  Adds a one time listener for the event event. The listener is removed after the first time the event is fired.

• removeListener(event, λ)

  Removes the listener λ for the event event.

Events:

• connect

  Fired when the connection is established and the handshake successful.

• connecting(transport_type)

  Fired when a connection is attempted, passing the transport name.

• connect_failed

  Fired when the connection timeout occurs after the last connection attempt. This only fires if the connectTimeout option is set. If the tryTransportsOnConnectTimeout option is set, this only fires once all possible transports have been tried.

• message(message)

  Fired when a message arrives from the server

• close

  Fired when the connection is closed. Be careful with using this event, as some transports will fire it even under temporary, expected disconnections (such as XHR-Polling).

• disconnect

  Fired when the connection is considered disconnected.

• reconnect(transport_type,reconnectionAttempts)

  Fired when the connection has been re-established. This only fires if the reconnect option is set.

• reconnecting(reconnectionDelay,reconnectionAttempts)

  Fired when a reconnection is attempted, passing the next delay for the next reconnection.

• reconnect_failed

  Fired when all reconnection attempts have failed and we where unsuccessful in reconnecting to the server.

Contributors

Guillermo Rauch <[e-mail]>

Arnout Kazemier <[e-mail]>

License

(The MIT License)

Copyright (c) 2010 LearnBoost <[e-mail]>

Permission is hereby granted, free of charge, to any person obtaining a copy of this software and associated documentation files (the 'Software'), to deal in the Software without restriction, including without limitation the rights to use, copy, modify, merge, publish, distribute, sublicense, and/or sell copies of the Software, and to permit persons to whom the Software is furnished to do so, subject to the following conditions:

The above copyright notice and this permission notice shall be included in all copies or substantial portions of the Software.

THE SOFTWARE IS PROVIDED 'AS IS', WITHOUT WARRANTY OF ANY KIND, EXPRESS OR IMPLIED, INCLUDING BUT NOT LIMITED TO THE WARRANTIES OF MERCHANTABILITY, FITNESS FOR A PARTICULAR PURPOSE AND NONINFRINGEMENT. IN NO EVENT SHALL THE AUTHORS OR COPYRIGHT HOLDERS BE LIABLE FOR ANY CLAIM, DAMAGES OR OTHER LIABILITY, WHETHER IN AN ACTION OF CONTRACT, TORT OR OTHERWISE, ARISING FROM, OUT OF OR IN CONNECTION WITH THE SOFTWARE OR THE USE OR OTHER DEALINGS IN THE SOFTWARE.