SSE stands for Server-Sent Events. It is a web standard technology that enables a server to push real-time updates to clients over a single, long-lived HTTP connection.

Key Features Link to heading

  • Server Push: The server can send messages at any time without the client needing to request them.
  • Automatic Reconnection: If the connection drops, the browser automatically reconnects and can resume from the last received event using last-event-id.
  • Simple Implementation: Requires minimal code on both client and server sides.
  • Built on HTTP: Works well with proxies, firewalls, and existing web infrastructure.
  • Event Support: You can send named events, data, IDs, and retry instructions.
  • Lightweight: Lower overhead compared to WebSocket for one-way streaming.

Use Cases Link to heading

  • Real-time notifications and alerts
  • Live dashboards and monitoring systems
  • Stock prices, cryptocurrency tickers, or sports scores
  • Progress tracking for long-running tasks (file uploads, exports, AI processing)
  • News feeds and social media updates
  • Live chat applications (for the server-to-client message stream)

Limitations Link to heading

  1. Unidirectional Only: Data flows only from server to client. For client-to-server communication, you still need Fetch, AJAX, or WebSocket.
  2. Text-Only: Does not support binary data natively (images, videos, etc.). You must convert them using Base64, which increases payload size.
  3. Browser Connection Limits: Most browsers limit concurrent SSE connections per domain (typically 6). Too many open streams can cause issues.
  4. Not Ideal for High-Frequency Bidirectional Apps: For real-time multiplayer games or complex chat systems, WebSocket is usually better.
  5. Server Timeouts: Some servers and proxies have default connection timeouts. You may need to configure keep-alive settings.
  6. CORS Considerations: Cross-origin requests require proper server headers.