What is Socket.IO?

Socket.IO is a JavaScript library that provides a higher-level abstraction over WebSockets with additional features. It consists of a server library (Node.js) and a client library (browser/Node). Key additions over raw WebSockets include: automatic reconnection when the connection drops, event-based communication (emit/on pattern instead of raw message strings), rooms and namespaces for organizing connections, broadcasting to multiple clients, fallback transports (falls back to HTTP long polling if WebSocket is unavailable), and acknowledgments for confirmed message delivery. Socket.IO does NOT use the standard WebSocket protocol by default — its protocol adds a layer on top, meaning Socket.IO clients and servers must both use the Socket.IO library.