# zloirock/core-js

Standard Library

Repository: https://github.com/zloirock/core-js
Canonical: https://ross.abutalabs.com/products/core-js
Homepage: https://core-js.io
Language: JavaScript
License: MIT
License Family: permissive
Topics: proposal, polyfill, shim, es6, es7, es2015, esnext, ponyfill, javascript, js, ecmascript-proposals, proposals
Last push: 2026-08-26T22:42:16+00:00

## Health v2 (maintenance only)
Score: 94/100 (v2, computed 2026-09-03T02:20:16.233290+00:00)
- activity 99, release rhythm 84, longevity 100
- inputs: {"age_days": 4795, "days_push": 7, "days_rel": 28, "gap_med": 51.0, "n_releases_24m": 13}
- flags: none
- formula: round(0.45*activity + 0.35*rhythm + 0.20*longevity); archived -> min(score, 10)

## Adoption (not part of the score)
Stars 25526, forks 1686 (observed 2026-08-28T04:11:38.223041+00:00)

## What it is
core-js is a modular JavaScript standard library providing polyfills for ECMAScript features up to 2025, TC39 proposals, and some WHATWG/W3C web standards like URL. It supports importing only needed features, pollution-free usage via core-js-pure, and automatic injection through tools like Babel and SWC.

## Use cases
- use modern JavaScript features in older browsers
- polyfill ES2025 features and TC39 proposals
- make code run consistently across browsers with engine bug fixes
- reduce bundle size by importing only required polyfills
- use polyfills without polluting the global namespace
- support new Set, Iterator, and Promise methods in older engines

## When to choose
- you need maximum ECMAScript coverage across old and new engines
- you want strict spec compliance and engine bug workarounds
- you use Babel or SWC and want automatic polyfill injection
- you need to polyfill early-stage TC39 proposals

## When to avoid
- you target only evergreen browsers and need no polyfills
- you want a minimal runtime with zero library overhead
- you need polyfills for non-JavaScript languages

## Facets
- artifact type: library
- maturity: active
- function: sdk, developer-tools, plugin-system
- domain: web-development, frontend, programming-languages, cross-platform
- platform: browser, bun, cross-platform
- tags: polyfill, javascript, ecmascript, esnext, shim, ponyfill, babel, compatibility, standard-library, nodejs, web-server, deno

## Member repositories
- zloirock/core-js (main) score 94

## Provenance
- Observed fields: from GitHub, fetched 2026-08-28T04:11:38.223041+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 2026-08-29T16:56:02.403103+00:00, confidence not recorded.
  - readme: https://github.com/zloirock/core-js (fetched 2026-08-28T04:11:38.223041+00:00, sha 3af38a66a0b9)
  - homepage: https://core-js.io (fetched 2026-08-29T07:53:10.225204+00:00, sha d45862a3705e)
  - site_page: https://core-js.io/docs (fetched 2026-08-29T07:53:10.234471+00:00, sha 1225e184d721)
  - site_page: https://core-js.io/changelog (fetched 2026-08-29T07:53:10.237209+00:00, sha 6abb46693d9f)
- Data as of 2026-08-30T08:39:29.467469+00:00.