# Yaffle/EventSource

a polyfill for http://www.w3.org/TR/eventsource/

Repository: https://github.com/Yaffle/EventSource
Canonical: https://ross.abutalabs.com/products/eventsource
Language: JavaScript
License: MIT
License Family: permissive
Last push: 2024-05-18T19:20:29+00:00

## Health v2 (maintenance only)
Score: 23/100 (v2, computed 2026-09-03T02:20:16.233290+00:00)
- activity 0, release rhythm 8, longevity 100
- inputs: {"age_days": 5652, "days_push": 837, "days_rel": null, "gap_med": null, "n_releases_24m": 0}
- flags: none
- formula: round(0.45*activity + 0.35*rhythm + 0.20*longevity); archived -> min(score, 10)

## Adoption (not part of the score)
Stars 2183, forks 335 (observed 2026-08-28T04:06:23.443081+00:00)

## What it is
A JavaScript polyfill for the EventSource (Server-Sent Events) API, providing support for older browsers like IE 8-10 and adding features such as custom headers and cross-domain requests. It is distributed as the 'event-source-polyfill' npm package and works with bundlers like webpack and browserify.

## Use cases
- consume server-sent events in browsers without native EventSource support
- add custom headers to EventSource requests for authentication
- use SSE with cross-domain (CORS) requests in legacy browsers
- support IE 10 and older browsers for real-time event streams
- integrate SSE into Angular or Ionic applications via polyfills
- send Last-Event-ID for stream reconnection in browsers lacking header support

## When to choose
- you need Server-Sent Events in legacy browsers like IE 8-10
- you need custom headers or Last-Event-ID query parameter support with EventSource
- you want cross-domain SSE with simple server-side requirements

## When to avoid
- your target browsers all support native EventSource
- you need bidirectional communication (use WebSockets instead)
- you need to support Android Browser or Opera Mini
- the maintainer explicitly discourages using this library for new projects

## Facets
- artifact type: library
- maturity: maintenance
- function: http-client, websocket
- domain: web-development, frontend, apis
- platform: browser, cross-platform
- tags: server-sent-events, eventsource, polyfill, sse, real-time, javascript

## Member repositories
- Yaffle/EventSource (main) score 23

## Provenance
- Observed fields: from GitHub, fetched 2026-08-28T04:06:23.443081+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 2026-08-30T02:48:14.548559+00:00, confidence not recorded.
  - readme: https://github.com/Yaffle/EventSource (fetched 2026-08-28T04:06:23.443081+00:00, sha a0655c5640ed)
- Data as of 2026-08-30T08:39:29.467469+00:00.