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Original author(s) Guillermo Rauch
Developer(s) Automattic
Stable release
2.0.3 / June 13, 2017 (2017-06-13)[1]
Repository Edit this at Wikidata
Development status Active
Written in JavaScript
Operating system Cross-platform
Type Event-driven networking
License MIT License[2]

Socket.IO is a JavaScript library for realtime web applications. It enables realtime, bi-directional communication between web clients and servers. It has two parts: a client-side library that runs in the browser, and a server-side library for Node.js. Both components have a nearly identical API. Like Node.js, it is event-driven.

Socket.IO primarily uses the WebSocket protocol with polling as a fallback option,[3] while providing the same interface. Although it can be used as simply a wrapper for WebSocket, it provides many more features, including broadcasting to multiple sockets, storing data associated with each client, and asynchronous I/O.

It can be installed with the npm tool.[4][5]


Socket.IO provides the ability to implement real-time analytics, binary streaming, instant messaging, and document collaboration.[6] Notable users include Microsoft Office, Yammer, and Zendesk.[7]

Socket.IO handles the connection transparently. It will automatically upgrade to WebSocket if possible. This requires the programmer to only have Socket.IO knowledge.

Socket.IO is not a WebSocket library with fallback options to other realtime protocols. It is a custom realtime transport protocol implementation on top of other realtime protocols. Its protocol negotiation parts cause a client supporting standard WebSocket to not be able to contact a Socket.IO server. And a Socket.IO implementing client cannot talk to a non-Socket.IO based WebSocket or Long Polling Comet server. Therefore, Socket.IO requires using the Socket.IO libraries on both client and server side.

As of version 2.0, Socket.IO makes use of µWebSockets as the underlying WebSocket library.[8]


  1. ^ "Release 2.0.3 · socketio/". GitHub. 
  2. ^ " at master · socketio/ · GitHub". GitHub. 
  3. ^ "socketio/". GitHub. 
  4. ^ "". 
  5. ^ "faq - npm Documentation". 
  6. ^
  7. ^ Paul Krill (2 June 2014). "Socket.IO JavaScript framework ready for real-time apps". InfoWorld. 
  8. ^ Damien Arrachequesne (13 May 2017). "Socket.IO 2.0.0 release post". 

External links[edit]