core-sse

Server-Sent Events (SSE) package for Node.js/Express (backend) and React/Next.js (frontend).

Features

• Express Middleware: Easily add SSE channels to your backend.
• React Hook: Subscribe to SSE channels in your frontend with useSSE.
• TypeScript Types: Shared types for both client and server usage.
• Heartbeat, Retry, Custom Events: Full support for SSE features.

Installation

npm install core-sse

Usage

Backend (Express)

import { sseMiddleware, sseEmitter, emitSSEEvent } from 'core-sse';

// Add SSE endpoint
app.get('/events/:channel', sseMiddleware);

// Broadcast an event to all clients on a channel
sseEmitter.emit('broadcast', {
  channel: 'user',
  event: 'user-update',
  data: { ...user },
});

// Or use emitSSEEvent directly
emitSSEEvent('user', 'user-update', { ...user });

Frontend (React)

import { useSSE } from 'core-sse';

const { data, isConnected, error } = useSSE('user', {
  baseUrl: 'http://localhost:4000', // or your production backend
  heartbeat: true,
  onMessage: (data) => { ... },
  onEvent: {
    'user-update': (data) => { ... },
  },
  onOpen: () => { ... },
  onClose: () => { ... },
  onError: (err) => { ... },
});

API Reference

Server

• sseMiddleware(req, res) — Express handler for SSE channels.
• sseEmitter — Node.js EventEmitter for broadcasting events.
• emitSSEEvent(channel, event, data) — Send a named event to all clients.
• emitSSEMessage(channel, data) — Send a default message to all clients.

Client

• useSSE(channel, options) — React hook for subscribing to SSE channels.
• Options: baseUrl, heartbeat, retryDelay, maxRetryDelay, onMessage, onEvent, onOpen, onClose, onError.

TypeScript Support

• All exports are fully typed for both client and server usage.

License

MIT