core-js

Window-level global the technology installs on page. Reproducible by typing the path into the DevTools console.

window.__core-js_shared__

window.__core-js_shared__.versions.0.version = ^(.+)$

window._babelPolyfill

window.core

window.core.version = ^(.+)$

How do I check if a website is using core-js?

Open the page in Chrome, click the Sourcemap Explorer toolbar icon, and read the Stack tab. The popup matches core-js's fingerprint signals (response headers, asset URL prefixes, runtime globals, sourcemap paths) and flags it whenever any combination is found. The same checks can be reproduced manually in DevTools — see the "How we detect" section above.

What core-js version can Sourcemap Explorer detect?

core-js ships as a hosted javascript libraries rather than a bundled npm package, so version-specific detection isn't always possible. Where the platform leaks a version in response headers (`X-Powered-By`, `Server`, generator meta tags) we surface it; otherwise we report presence only.

Is core-js open source?

Yes, core-js is open source. The license details are listed on the official site (https://github.com/zloirock/core-js), and the codebase typically lives on a public source-control host.

Where can I read more about core-js?

Official site: https://github.com/zloirock/core-js. For Sourcemap Explorer's detection guide, see the deep-dive link below or the related guides in the cross-link section.