socket.io

Real-time, bidirectional event-based communication for Node.js — WebSockets with automatic fallback, rooms, namespaces, and horizontal scaling support.

socket.io

Node.js

Real-time, bidirectional event-based communication for Node.js — WebSockets with automatic fallback, rooms, namespaces, and horizontal scaling support.

npm GitHub Docs

Fit

Bundle (gzip)

54.7 kB

265.2 kB raw

Install size includes transitive dependencies. Bundle size is gzipped browser payload.

Freshness

The Problem

Building real-time features (chat, live notifications, collaborative editing) over raw WebSockets requires handling reconnection, broadcasting to groups of clients, and dealing with environments that block WebSocket connections.

What It Does

Socket.IO abstracts WebSockets with automatic HTTP long-polling fallback, built-in reconnection logic, and a rooms API for broadcasting to subsets of connected clients. Namespaces let you multiplex multiple channels over a single connection, and the adapter system enables horizontal scaling with Redis.

Installation

bash

npm install socket.io

Usage Example

typescript

import { Server } from 'socket.io';
import { createServer } from 'http';

const httpServer = createServer();
const io = new Server(httpServer, { cors: { origin: '*' } });

io.on('connection', (socket) => {
  console.log('User connected:', socket.id);

  socket.on('join-room', (roomId) => socket.join(roomId));

  socket.on('send-message', ({ roomId, message }) => {
    io.to(roomId).emit('new-message', { from: socket.id, message });
  });

  socket.on('disconnect', () => console.log('User left:', socket.id));
});

httpServer.listen(3001);

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