core-js is a modular JavaScript standard library that provides polyfills (shims) for ECMAScript features and some web standards, with options to load only the parts you need. It helps developers use modern JavaScript features in environments that may not support them, and it can be used without polluting the global namespace (for example via core-js-pure).
Project status
- Actively maintained, evolving: The upstream GitHub repo shows recent activity (last push on 2026-05-30), and the project continues to ship v3.x updates plus a v4.0.0-alpha.1 update, indicating ongoing development rather than maintenance mode.
- Apparent update cadence: Observed updates include v3.48.0 (2026-01-21), v3.49.0 (2026-03-16), and v4.0.0-alpha.1 (2026-03-22), suggesting a roughly 1 to 2 month cadence for v3, followed by a near-term v4 alpha, though the evidence only covers these specific points.
AI summary generated Today
Recent updates
v4.0.0-alpha.1
2 months agoThe release notes for v4.0.0-alpha.1 are effectively a placeholder and do not document specific technical changes. The code diff, however, shows significant repository and build-system modifications, including a major licensing change and removal of the Deno core-js entry files.
Breakingv3.49.0
2 months agocore-js v3.49.0 includes a large batch of polyfill correctness and accuracy fixes, plus some spec alignment for iterator helpers. The release notes emphasize improvements to Iterator.range behavior, numeric formatting polyfills, and multiple iterator, URL, RegExp, and typed array fixes.
Breakingv3.48.0
4 months agocore-js v3.48.0 adds Map and WeakMap upsert APIs (getOrInsert and getOrInsertComputed) and updates compat data to reflect shipping status in major engines. The diff also shows improvements to polyfill correctness (CreateDataProperty usage, RegExp constructor tweaks) and several documentation updates to include the new entry points. Additionally, multiple repository CI workflows were changed to use newer GitHub Actions versions and a different install step.
Featuresv3.47.0
6 months agocore-js v3.47.0 updates iterator sequencing and JSON parse with source text support, moving the related built-ins into stable ES module entry points. The release also updates compat data mappings and fixes an IE8- polyfill size regression. The code diff shows several module and metadata refactors that are not explicitly called out in the release notes.
Featuresv3.46.0
7 months agocore-js 3.46.0 updates polyfills related to the TC39 Iterator chunking proposal (including `Iterator.prototype.windows` changes), and fixes several iterator and grouping edge cases. The release also updates compat data mappings for multiple engines and introduces a documentation site migration to core-js.io.
BreakingFeaturesv3.45.1
9 months agocore-js v3.45.1 primarily fixes how Map getOrInsert polyfills behave in the pure build when native upsert-style methods exist. It also updates core-js-compat data (Bun 1.2.20 shipped markers, Samsung Internet 29, Electron 39) and adds `bugs` metadata to package.json files across the monorepo.
v3.45.0
10 months agocore-js 3.45.0 updates polyfills by promoting several proposals to stable (notably Uint8Array base64/hex, Math.sumPrecise, Iterator.concat, and Map/WeakMap upsert). The release notes describe the new built-ins and added namespace modules, plus compat-data adjustments for specific browser behavior. The code diff shows additional bundling and dependency-graph changes that are not explicitly mentioned in the release notes.
Featuresv3.44.0
11 months agocore-js 3.44.0 updates multiple proposal-stage polyfills and fixes, most notably adding `Iterator.prototype.sliding` (iterator chunking stage 2.0) and adjusting iterator sequencing behaviors. It also includes the specified `Uint8Array` base64/hex stage 3 bug fixes, `Number.prototype.clamp` NaN handling changes, and broad compat data updates for newer engine versions.
BreakingFeaturesv3.43.0
11 months agocore-js v3.43.0 adds stable ES namespace entries for several Explicit Resource Management proposals (Symbol.dispose, Symbol.asyncDispose, SuppressedError, DisposableStack, AsyncDisposableStack, and iterator dispose methods), and it also incorporates new proposal built-ins like Array.fromAsync and several Iterator helpers. The release notes emphasize standards progress (moving to stable/stage) and compat-data updates across browsers and runtimes.
BreakingFeaturesv3.42.0
4/29/2025core-js 3.42.0 updates iterator helper behavior to align with TC39/ecma262 changes, primarily by adding early-error iterator closing (including WebKit-specific fixes). It also updates core-js-compat to support `targets.esmodules: 'intersect'` and refreshes compatibility mapping data for multiple environments.
BreakingFeatures