# EventSource/eventsource

EventSource client for Node.js, browsers and other JavaScript runtimes

Repository: https://github.com/EventSource/eventsource
Canonical: https://ross.abutalabs.com/products/eventsource-eventsource
Language: TypeScript
License: MIT
License Family: permissive
Topics: eventsource, sse, server-sent-events
Last push: 2026-08-20T19:58:10+00:00

## Health v2 (maintenance only)
Score: 98/100 (v2, computed 2026-09-03T02:20:16.233290+00:00)
- activity 98, release rhythm 98, longevity 100
- inputs: {"age_days": 5320, "days_push": 13, "days_rel": 13, "gap_med": 5, "n_releases_24m": 14}
- flags: none
- formula: round(0.45*activity + 0.35*rhythm + 0.20*longevity); archived -> min(score, 10)

## Adoption (not part of the score)
Stars 1155, forks 266 (observed 2026-08-28T04:03:47.779478+00:00)

## What it is
A WhatWG/W3C-compliant EventSource client library for consuming server-sent events (SSE) in Node.js, browsers, Deno, Bun, and other JavaScript runtimes. It implements the spec with minimal additions and supports reconnection, typed event listeners, and explicit connection closing.

## Use cases
- consume server-sent events in node.js
- subscribe to an SSE endpoint from the browser
- listen for real-time updates over HTTP streams
- polyfill EventSource in runtimes without native support
- stream live notifications from a server
- connect to an SSE API with automatic reconnection

## When to choose
- you need a spec-compliant EventSource client across Node.js and browsers
- your runtime lacks a native EventSource implementation
- you want a minimal, standards-based SSE consumer
- you need broad runtime support including Deno and Bun

## When to avoid
- you need bidirectional streaming or a richer client API (consider eventsource-client)
- you need WebSockets or two-way communication
- you must support very old runtimes without private class fields (use the 4.x branch instead)

## Facets
- artifact type: library
- maturity: stable
- function: http-client, websocket
- domain: web-development, frontend, backend, apis
- platform: browser, bun, cross-platform
- tags: server-sent-events, sse, eventsource, typescript, whatwg, real-time, nodejs, deno

## Member repositories
- EventSource/eventsource (main) score 98

## Provenance
- Observed fields: from GitHub, fetched 2026-08-28T04:03:47.779478+00:00.
- Health v2: computed from the inputs above; adoption is never an input.
- Inferred fields (summary, facets, guidance): AI-extracted, prompt v1, taxonomy v1, on 2026-08-30T06:32:10.634620+00:00, confidence not recorded.
  - readme: https://github.com/EventSource/eventsource (fetched 2026-08-28T04:03:47.779478+00:00, sha fc6131530d95)
  - registry_npm: https://registry.npmjs.org/eventsource (fetched 2026-08-29T12:37:42.241965+00:00, sha a282e3d8f1c3)
- Data as of 2026-08-30T08:39:29.467469+00:00.