Express Server-Sent Events Middleware

express-sse-middleware is an npm package providing a robust Express.js middleware for implementing Server-Sent Events (SSE) in Node.js applications. It simplifies the process of pushing real-time updates from a server to clients over a single HTTP connection, making it suitable for dashboards, chat applications, and live data feeds. The current stable version is 3.0.3, released after a significant v3.0.0 update which transitioned the package to an ES Module (ESM) first architecture. While a strict release cadence isn't explicitly defined, the package appears actively maintained given recent major version bumps and ongoing development. Its primary differentiator is its straightforward integration into existing Express applications by extending the `Response` object with a dedicated `sse()` method, allowing developers to easily send data, custom events, and IDs to connected clients. It also offers an `EventBuilder` for more structured event creation, though direct string sending is fully supported and often sufficient for simple use cases.