date-fns

About

Modern JavaScript date utility library

What detecting date-fns tells you about a site

date-fns reveals a functional, tree-shakeable approach to dates — pure functions imported individually rather than a monolithic object — chosen by teams that care about bundle size and immutability. Its presence is a strong marker of a modern, performance-conscious build.

Why the exact date-fns version matters

date-fns v3 reorganised the package exports and v4 added first-class time-zone support; the exact version tells you which import surface and time-zone story the code relies on.

date-fns in a real-world stack

When you find date-fns in a bundle, it rarely travels alone. Frequently alongside react-day-picker or a form library's date inputs, and a build that tree-shakes the unused functions away.

Quick facts

How Sourcemap Explorer detects date-fns

date-fns ships as v4.4.0, published 2026-05-29 and carries 0 direct dependencies, 209 versions on the registry. Those exact numbers are the footprint Sourcemap Explorer matches when date-fns rides inside a deployed bundle — here is how the detection works.

We catch date-fns from two complementary signals: bundled source paths and the embedded package.json. Modern bundlers (webpack, Vite, esbuild, Rollup, Turbopack) preserve the original node_modules/date-fns/ 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. 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 — that map is where the `date-fns` paths live.

2. 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/date-fns/` — every match confirms the package is bundled. The matching `sourcesContent[i]` for `node_modules/date-fns/package.json` gives you the exact installed version.

3. 3

   Read the version directly from package.json

   Run `jq -r '. as $m | $m.sources | to_entries[] | select(.value | endswith("node_modules/date-fns/package.json")) | $m.sourcesContent[.key] | fromjson | .version' bundle.js.map`. Sourcemap Explorer automates the same query in the popup.

Major releases of date-fns

When each major version first landed. Major bumps are where breaking changes live, so this timeline is the fastest way to date the date-fns version a site actually ships against the ecosystem.

Recent versions

date-fns README

Live mirror of the GitHub README, for reference. Updated whenever the repo's default branch changes.

🔥️ NEW: date-fns v4.0 with first-class time zone support is out!

date-fns provides the most comprehensive, yet simple and consistent toolset for manipulating JavaScript dates in a browser & Node.js

👉 Documentation

👉 Blog

---

It's like Lodash for dates

• It has 200+ functions for all occasions.
• Modular: Pick what you need. Works with webpack, Browserify, or Rollup and also supports tree-shaking.
• Native dates: Uses existing native type. It doesn't extend core objects for safety's sake.
• Immutable & Pure: Built using pure functions and always returns a new date instance.
• TypeScript: The library is 100% TypeScript with brand-new handcrafted types.
• I18n: Dozens of locales. Include only what you need.
• and many more benefits

import { compareAsc, format } from "date-fns";

format(new Date(2014, 1, 11), "yyyy-MM-dd");
//=> '2014-02-11'

const dates = [
  new Date(1995, 6, 2),
  new Date(1987, 1, 11),
  new Date(1989, 6, 10),
];
dates.sort(compareAsc);
//=> [
//   Wed Feb 11 1987 00:00:00,
//   Mon Jul 10 1989 00:00:00,
//   Sun Jul 02 1995 00:00:00
// ]

The library is available as an npm package. To install the package run:

npm install date-fns --save

Docs

See date-fns.org for more details, API, and other docs.

License

MIT © Sasha Koss

FAQ