# date-fns: what changed from 3 to 4

- Product: date-fns (https://whatsnew.fyi/product/date-fns)
- Vendor: date-fns
- Range: changelog entries numbered after v3.6.0 up to and including v4.4.0, stable releases only
- Entries below: 6 releases (newest first)
- Resolved: 3 is v3.6.0 and 4 is v4.4.0, the newest stable release of each major we track
- Carrying security changes: 0 · CVEs mentioned: 0 · Mentioning breaking changes: 2 · Removing or deprecating something: 1
- Page: https://whatsnew.fyi/product/date-fns/compare/3...4

What's New is an index, not a publisher: every entry below links to the vendor's own release notes, which are the authoritative source. Entries are labelled where they are hand-curated sample data, pre-releases, or drawn from a secondary source such as a developer blog.

Reuse: the summaries, labels and curation here are © What's New. Quote freely with attribution and a link back; wholesale republication of the corpus is not permitted — terms: https://whatsnew.fyi/terms. The vendors' own release notes remain their publishers'.

## What changed (16 changes, grouped by kind)

### Added

#### v4.4.0 (2026-05-29)

- Introduced new package @date-fns/cdn for CDN usage

#### v4.1.0 (2024-09-17)

- Add time zone support to format, formatISO, formatISO9075, formatRelative, and formatRFC3339

#### v4.0.0 (2024-09-16)

- Add time zones support via @date-fns/tz's TZDate class and tz helper function
- All relevant functions now accept the context in option to specify the time zone for calculations

### Changed

#### v4.2.0 (2026-05-18)

- Added Temporal API references to the JSDoc annotations of add, addBusinessDays, and addDays

#### v4.0.0 (2024-09-16)

- Function arguments and Interval's start and end can now be of different types, allowing mixing of UTCDate, TZDate, Date, and other extensions with primitives
- Functions now normalize mixed date type values, make calculations, and return results in the same type as inferred from the context in option or first encountered argument object type
- Package is now ESM-first with CommonJS still supported

### Fixed

#### v4.3.0 (2026-05-22)

- Fixed missing modularized optimization fallback for Next.js and others
- Fixed pt locale first day of week to be Sunday
- Fixed zh-CN, zh-HK, and zh-TW locale month parsing for October, November, and December

#### v4.2.1 (2026-05-18)

- Fixed type definitions missing in v4.2.0 due to TypeScript misconfiguration

#### v4.1.0 (2024-09-17)

- Fix internal constructFrom throwing an exception on null arguments, now returns Invalid Date or NaN instead

#### v4.0.0 (2024-09-16)

- Fixed CDN build compatibility with jQuery and other tools that expose $ by properly wrapping the code in an IIFE

### Removed

#### v4.4.0 (2026-05-29)

- Removed CDN source maps to reduce the package size

### Deprecated

#### v4.4.0 (2026-05-29)

- The date-fns CDN scripts are now deprecated and will be removed in the next major release

## Release notes

### v4.4.0

- Date: 2026-05-29
- Version: v4.4.0
- Original notes: https://github.com/date-fns/date-fns/releases/tag/v4.4.0
- Permalink: https://whatsnew.fyi/product/date-fns/releases/v4.4.0

- **deprecated** — The date-fns CDN scripts are now deprecated and will be removed in the next major release
- **removed** — Removed CDN source maps to reduce the package size
- **added** — Introduced new package @date-fns/cdn for CDN usage

This release revisits the approach to CDN usage and introduces a new package, `@date-fns/cdn` and deprecates the `date-fns` CDN scripts. It allowed reducing the zipped package size from `5.83 MB` down to `3.96 MB` without introducing any breaking changes.

In `v5.0.0-alpha.0` where CDN scripts are completely removed from `date-fns` the change is more significant and brings the zipped package size down to `2.89 MB`.

It is just the first step in optimizing the package size. Expect further size reduction in the future v4 and v5 versions.

###### Changed

- **DEPRECATED**: The `date-fns` CDN scripts are now deprecated and will be removed in the next major release. Please switch to the new `@date-fns/cdn` package for CDN usage.

- Removed CDN source maps to reduce the package size. If you rely on them, please switch to the new `@date-fns/cdn` package that still includes them.

### v4.3.0

- Date: 2026-05-22
- Version: v4.3.0
- Original notes: https://github.com/date-fns/date-fns/releases/tag/v4.3.0
- Permalink: https://whatsnew.fyi/product/date-fns/releases/v4.3.0

- **fixed** — Fixed missing modularized optimization fallback for Next.js and others
- **fixed** — Fixed pt locale first day of week to be Sunday
- **fixed** — Fixed zh-CN, zh-HK, and zh-TW locale month parsing for October, November, and December

Kudos to [@ImRodry](https://github.com/ImRodry) and [@puneetdixit200](https://github.com/puneetdixit200) for their contributions.

###### Fixed

- Fixed missing modularized optimization fallback ([for Next.js and others](https://x.com/kossnocorp/status/1731181274579325260)). See [#4193](https://x.com/kossnocorp/status/1731181274579325260).

- Fixed `pt` locale first day of week to be Sunday. See [#4195](https://github.com/date-fns/date-fns/pull/4195) by [@ImRodry](https://github.com/ImRodry).

- Fixed `zh-CN`, `zh-HK`, and `zh-TW` locale month parsing for October, November, and December. See [#4194](https://github.com/date-fns/date-fns/pull/4194) by [@puneetdixit200](https://github.com/puneetdixit200).

### v4.2.1

- Date: 2026-05-18
- Version: v4.2.1
- Original notes: https://github.com/date-fns/date-fns/releases/tag/v4.2.1
- Permalink: https://whatsnew.fyi/product/date-fns/releases/v4.2.1

- **fixed** — Fixed type definitions missing in v4.2.0 due to TypeScript misconfiguration

###### Fixed

- Fixed type definitions missing in v4.2.0 due to TypeScript misconfiguration.

### v4.2.0

- Date: 2026-05-18
- Version: v4.2.0
- Original notes: https://github.com/date-fns/date-fns/releases/tag/v4.2.0
- Permalink: https://whatsnew.fyi/product/date-fns/releases/v4.2.0

- **changed** — Added Temporal API references to the JSDoc annotations of add, addBusinessDays, and addDays

This is a minor release in all senses, it only includes documentation updates (first of many) that points to the new [You Don't Need date-fns\*](https://date-fns.org/you-dont-need-date-fns) page.

\* Not really

###### Changed

- Added Temporal API references to the JSDoc annotations of `add`, `addBusinessDays`, and `addDays`.

### v4.1.0

- Date: 2024-09-17
- Version: v4.1.0
- Original notes: https://github.com/date-fns/date-fns/releases/tag/v4.1.0
- Permalink: https://whatsnew.fyi/product/date-fns/releases/v4.1.0

- **added** — Add time zone support to format, formatISO, formatISO9075, formatRelative, and formatRFC3339
- **fixed** — Fix internal constructFrom throwing an exception on null arguments, now returns Invalid Date or NaN instead

This release adds time zone support to format functions (that I somehow missed when working on the feature) and fixes a few bugs.

Make sure also upgrade `TZDate` to v1.0.2 as it [includes a bunch of critical bug fixes](https://github.com/date-fns/tz/blob/main/CHANGELOG.md#v102---2024-09-14).

###### Fixed

- Fixed internal `constructFrom` throwing an exception on `null` arguments. While `null` isn't allowed, the functions should rather return `Invalid Date` or `NaN` in such cases. See [#3885](https://github.com/date-fns/date-fns/issues/3885).

###### Added

- Added missing time zone support to `format`, `formatISO`, `formatISO9075`, `formatRelative` and `formatRFC3339`. See [#3886](https://github.com/date-fns/date-fns/issues/3886).

### v4.0.0

- Date: 2024-09-16
- Version: v4.0.0
- Original notes: https://github.com/date-fns/date-fns/releases/tag/v4.0.0
- Permalink: https://whatsnew.fyi/product/date-fns/releases/v4.0.0

- **added** — Add time zones support via @date-fns/tz's TZDate class and tz helper function
- **added** — All relevant functions now accept the context in option to specify the time zone for calculations
- **changed** — Function arguments and Interval's start and end can now be of different types, allowing mixing of UTCDate, TZDate, Date, and other extensions with primitives
- **changed** — Functions now normalize mixed date type values, make calculations, and return results in the same type as inferred from the context in option or first encountered argument object type
- **changed** — Package is now ESM-first with CommonJS still supported
- **fixed** — Fixed CDN build compatibility with jQuery and other tools that expose $ by properly wrapping the code in an IIFE

I have great news! First, ten years after its release, date-fns finally gets first-class time zone support.

Another great news is that there aren't many breaking changes in this release. All of them are type-related and will affect only those explicitly using internal date-fns types. Finally, it has been less than a year since the last major release, which is an improvement over the previous four years between v2 and v3. I plan on keeping the pace and minimizing breaking changes moving forward.

[Read more about the release in the announcement blog post](https://blog.date-fns.org/v40-with-time-zone-support/).

\- [Sasha @kossnocorp](https://twitter.com/kossnocorp)

###### Added

- Added time zones support via [`@date-fns/tz`](https://github.com/date-fns/tz)'s `TZDate` class and `tz` helper function. See its [README](https://github.com/date-fns/tz) for the details about the API.

- All relevant functions now accept the context `in` option, which allows to specify the time zone to make the calculations in. If the function also returns a date, it will be in the specified time zone:

  ```ts
  import { addDays, startOfDay } from "date-fns";
  import { tz } from "@date-fns/tz";

  startOfDay(addDays(Date.now(), 5, { in: tz("Asia/Singapore") }));
  //=> "2024-09-16T00:00:00.000+08:00"
  ```

  In the example, `addDays` will get the current date and time in Singapore and add 5 days to it. `startOfDay` will inherit the date type and return the start of the day in Singapore.

###### Changed

- The function arguments, as well as `Interval`'s `start` and `end`, now can be of different types, allowing you to mix `UTCDate`, `TZDate`, `Date`, and other extensions, as well as primitives (strings and numbers).

  The functions will normalize these values, make calculations, and return the result in the same type, preventing any bugs caused by the discrepancy. If passed, the type will be inferred from the context `in` option or the first encountered argument object type. The `Interval`'s `start` and `end` will be considered separately, starting from `start`.

  In the given example, the result will be in the `TZDate` as the first argument is a number, and the `start` takes precedence over the `end`.

  ```ts
  clamp(Date.now(), {
    start: new TZDate(start, "Asia/Singapore"),
    end: new UTCDate(),
  });
  //=> TZDate
  ```

- **BREAKING**: This release contains a bunch of types changes that should not affect the library's expected usage. The changes are primarily internal and nuanced, so rather than listing them here, I recommend you run the type checker after the upgrade. If there are unfixable problems, please [open an issue](https://github.com/date-fns/date-fns/issues/new).

- **BREAKING**: The package is now ESM-first. CommonJS is still supported, and it should not affect most users, but it might break in certain environments. If you encounter any issues, please [report them](https://github.com/date-fns/date-fns/issues/new).

###### Fixed

- Fixed CDN build compatibility with jQuery and other tools that expose `$` by properly wrapping the code in an IIFE.