Socket.IO is the real-time-communication library that abstracts WebSockets, long polling, and Server-Sent Events behind a single event-based API. It was the default choice for chat, multiplayer, and collaborative-editing features in Node.js applications through the 2014-2020 era.
Modern projects often skip Socket.IO and use raw WebSockets directly because the underlying browser support is now universal and the abstraction overhead is no longer worth it. Socket.IO is still relevant for projects that need its specific features: automatic reconnection, fallback transports, namespaces and rooms, broadcasting, and the scale-out via Redis adapters for multi-server deployments.
