underscore
JavaScript's functional programming helper library.
About
JavaScript's functional programming helper library.
Live mirror of the GitHub README. Updated whenever the repo's default branch changes.
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Underscore.js is a utility-belt library for JavaScript that provides support for the usual functional suspects (each, map, reduce, filter...) without extending any core JavaScript objects.
For Docs, License, Tests, and pre-packed downloads, see: https://underscorejs.org
For support and questions, please consult our security policy, the gitter channel or stackoverflow
Underscore is an open-sourced component of DocumentCloud: https://github.com/documentcloud
Many thanks to our contributors: https://github.com/jashkenas/underscore/contributors
You can support the project by donating on Patreon. Enterprise coverage is available as part of the Tidelift Subscription.
This project adheres to a code of conduct. By participating, you are expected to uphold this code.
Quick facts
npm install underscoreHow Sourcemap Explorer detects underscore
We catch underscore from two complementary signals: bundled source paths and the embedded package.json. Modern bundlers (webpack, Vite, esbuild, Rollup, Turbopack) preserve the original node_modules/underscore/ paths inside the JavaScript sourcemap's sources[] array — that's the canonical signal. When the matching package.json is also captured in sourcesContent[], we read the exact version field — patch number included. No regex guessing, no version inference.
- 1
Confirm the site exposes sourcemaps
In DevTools Network, check the response headers of any application script for `SourceMap` or `X-SourceMap`. Failing that, fetch the script's last 4 KB and look for a `//# sourceMappingURL=` comment.
- 2
Find the package in the bundle
Open DevTools → Network → reload. Click any application script and look at its sourcemap. Inside, search `sources[]` for entries matching `node_modules/underscore/` — every match confirms the package is bundled. The matching `sourcesContent[i]` for `node_modules/underscore/package.json` gives you the exact installed version.
- 3
Read the version directly from package.json
Run `jq -r '. as $m | $m.sources | to_entries[] | select(.value | endswith("node_modules/underscore/package.json")) | $m.sourcesContent[.key] | fromjson | .version' bundle.js.map`. Sourcemap Explorer automates the same query in the popup.
Recent versions
FAQ
What is underscore used for?
JavaScript's functional programming helper library.
How can I tell if a website is using underscore?
Open the page in Chrome with the Sourcemap Explorer extension installed and read the Stack tab. We catch `underscore` from two complementary signals: `node_modules/underscore/` paths inside the JavaScript sourcemap, and the embedded `package.json` we read for exact-version detection. Without the extension you can do the same lookup manually in DevTools — the steps are listed in the "How Sourcemap Explorer detects" section above.
What is the latest version of underscore?
1.13.8, as published on the npm registry. The "Recent versions" table on this page lists the most recent 8 releases with their release dates. Sourcemap Explorer reports the version actually bundled into a site, which can lag the latest release by months on real-world deployments.
Where can I read more?
Project homepage: https://underscorejs.org. Source code: https://github.com/jashkenas/underscore. Published on npm: https://www.npmjs.com/package/underscore. Licensed as MIT.
Detected by Sourcemap Explorer
When a bundle ships sourcemaps, we read the embedded package.json for underscore and report the precise version. Without sourcemaps, an import / require in the page's scripts is enough to flag it.