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Original author(s) Guillermo Rauch
Developer(s) Automattic
Stable release
1.7.3 / February 17, 2017 (2017-02-17)[1]
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.


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