feat!: defaults `fixedExtension` to true when platform is `node` #517

sxzz · 2025-09-28T22:53:57Z

Description

Defaults fixedExtension to true when platform is node.

Linked Issues

Additional context

netlify · 2025-09-28T22:54:02Z

✅ Deploy Preview for tsdown ready!

Name	Link
🔨 Latest commit	`bf400bd`
🔍 Latest deploy log	https://app.netlify.com/projects/tsdown/deploys/6902ce0719293b0008c19a78
😎 Deploy Preview	https://deploy-preview-517--tsdown.netlify.app
📱 Preview on mobile	Toggle QR Code... Use your smartphone camera to open QR code link.

To edit notification comments on pull requests, go to your Netlify project configuration.

pkg-pr-new · 2025-09-28T22:54:24Z

Open in StackBlitz

npm i https://pkg.pr.new/tsdown@517

npm i https://pkg.pr.new/create-tsdown@517

commit: bf400bd

RobinTail · 2025-11-04T16:16:02Z

This should depend on type in package.json by default

sxzz · 2025-11-04T16:18:21Z

See also https://bsky.app/profile/sxzz.dev/post/3lzwm2sgaus2z

silverwind · 2025-11-05T16:48:11Z

I see .mjs as a legacy solution and strongly prefer .js, so this change caught me by surprise.

It broke my lib because in package.json I have "exports": "./dist/index.js" which after this change pointed to a non-existing file.

kitschpatrol · 2025-11-05T17:46:00Z

I personally agree with Bjorn Lu's take on this — but if this is to be the default behavior in tsdown, maybe the fixedExtension option flag can be exposed in the CLI?

I had a bunch of projects that worked perfectly with a vanilla tsdown command and no additional configuration, which will now require a tsdown.config.ts file to bypass this default. Appending a flag would be cleaner for these cases.

Thanks for your work!

sxzz · 2025-11-05T18:41:59Z

All options can be overridden via CLI flags. To disable a boolean option, use --no-fixed-extension (--no-<option-name>).
You can also enable exports option to automatically generate exports field on package.json.

Thank you for your understanding.

kitschpatrol · 2025-11-05T18:46:29Z

Thanks! I didn't realize all the options are available as CLI flags, thought it was limited to https://tsdown.dev/reference/cli and what's documented in the --help output.

molvqingtai · 2025-11-11T02:12:04Z

Although configuration options are provided, it is still hoped that the default should follow the package.json type, or it should be the default --no-fixed-extension, generating code that is more in line with expectations in the case of minimal configuration or no configuration.

sxzz · 2025-11-11T07:02:25Z

v0.16 has been released for some time now, so we can no longer change the default behavior without affecting those who have already migrated. In the future, tsdown will be more cautious when introducing breaking changes.

Following rolldown/tsdown#517, `fixedExtension` is now on by default for node applications, which means that everything that it's emitting `mjs` for any esm js files and `.d.mts` for esm type declarations.

…#565)  ## PR Checklist - [ ] Addresses an existing open issue: fixes #000 - [ ] That issue was marked as [`status: accepting prs`](https://github.com/JoshuaKGoldberg/package-json-validator/issues?q=is%3Aopen+is%3Aissue+label%3A%22status%3A+accepting+prs%22) - [x] Steps in [CONTRIBUTING.md](https://github.com/JoshuaKGoldberg/package-json-validator/blob/main/.github/CONTRIBUTING.md) were taken ## Overview (This was failing in the renovate PR: https://github.com/JoshuaKGoldberg/package-json-validator/pulls) Following rolldown/tsdown#517, `fixedExtension` is now on by default when the platform is node, which means that it's emitting `mjs` for any esm js files and `.d.mts` for esm ts files. --------- Co-authored-by: renovate[bot] <29139614+renovate[bot]@users.noreply.github.com>

(This was failing in the renovate PR: #1373) Following rolldown/tsdown#517, fixedExtension is now on by default when the platform is node, which means that it's emitting mjs for any esm js files and .d.mts for esm ts files.

…#1386)  ## PR Checklist - [ ] Addresses an existing open issue: fixes #000 - [ ] That issue was marked as [`status: accepting prs`](https://github.com/JoshuaKGoldberg/eslint-plugin-package-json/issues?q=is%3Aopen+is%3Aissue+label%3A%22status%3A+accepting+prs%22) - [x] Steps in [CONTRIBUTING.md](https://github.com/JoshuaKGoldberg/eslint-plugin-package-json/blob/main/.github/CONTRIBUTING.md) were taken ## Overview (This was failing in the renovate PR: #1373) Following rolldown/tsdown#517, `fixedExtension` is now on by default when the platform is node, which means that it's emitting `mjs` for any esm js files and `.d.mts` for esm ts files. --------- Co-authored-by: renovate[bot] <29139614+renovate[bot]@users.noreply.github.com>

NiklasDah · 2025-11-14T12:39:56Z

v0.16 has been released for some time now, so we can no longer change the default behavior without affecting those who have already migrated. In the future, tsdown will be more cautious when introducing breaking changes. (@sxzz)

Would it at least be possible to update the breaking-changes section to clarify the impact of this change? The current entry:

Defaults fixedExtension to true when platform is node

doesn’t explain why this is breaking. I overlooked it and ran into unexpected bugs even after checking the release notes. Adding something like

this means that no .js-files will be created by default

retroacively, would help users better understand the impact when skimming the changelog.

sxzz · 2025-11-15T04:11:59Z

The changelog has been updated in the release notes: https://github.com/rolldown/tsdown/releases/tag/v0.16.0

Thank you for your feedback!

- See rolldown/tsdown#517

DopamineDriven · 2025-11-21T18:12:21Z

This should definitely depend on type in package.json by default. That's by convention

this breaks pipelines unnecessarily

silverwind · 2025-11-21T18:16:31Z

I'd make it by default match the extension of the entry file. And maybe add a option outputExtension or similar so users can specify the extension they want.

sxzz · 2025-11-22T05:10:12Z

You can use outExtensions

## PR Checklist - [x] Addresses an existing open issue: fixes #2287 - [x] That issue was marked as [`status: accepting prs`](https://github.com/JoshuaKGoldberg/create-typescript-app/issues?q=is%3Aopen+is%3Aissue+label%3A%22status%3A+accepting+prs%22) - [x] Steps in [CONTRIBUTING.md](https://github.com/JoshuaKGoldberg/create-typescript-app/blob/main/.github/CONTRIBUTING.md) were taken ## Overview Bumps everything to latest using `ncu -u`, except: * `zod` and `zod-package-json`: because Bingo is still on v3 * `eslint-plugin-package-json`: pending the refresh of ESLint settings in #2275, only bumps a few minors The main changes are: * Removing unnecessary `files` entries in `package.json`, courtesy of `eslint-plugin-package-json` & `package-json-validator` updates: JoshuaKGoldberg/eslint-plugin-package-json#1232 & co. * Explicitly defaulting `fixedExtension` to `false`, courtesy of rolldown/tsdown#517 🎁

sxzz changed the title ~~feat!: defaults fixedExtension to true if platform is node~~ feat!: defaults fixedExtension to true when platform is node Sep 28, 2025

sxzz added 2 commits October 30, 2025 10:31

feat!: defaults fixedExtension to true if platform is node

1c774ed

chore: update snapshot

bf400bd

sxzz force-pushed the feat/fixed-extension branch from 6b76efb to bf400bd Compare October 30, 2025 02:31

sxzz merged commit e1168a2 into main Oct 30, 2025
17 checks passed

sxzz deleted the feat/fixed-extension branch October 30, 2025 02:33

sxzz mentioned this pull request Nov 5, 2025

Version 0.16.0 does not respect "type": "module" in `package.json and produce wrong output. #583

Closed

hi-ogawa mentioned this pull request Nov 10, 2025

fix(deps): update all non-major dependencies vitejs/vite-plugin-react#968

Merged

1 task

AriPerkkio mentioned this pull request Nov 10, 2025

chore(deps): update all non-major npm dependencies AriPerkkio/ast-v8-to-istanbul#106

Merged

1 task

cb1kenobi mentioned this pull request Nov 11, 2025

Update ESM export to be .mjs extension HarperFast/rocksdb-js#224

Merged

michaelfaith mentioned this pull request Nov 12, 2025

build: update package.json entries with explicit mjs / mts extensions JoshuaKGoldberg/package-json-validator#565

Merged

3 tasks

sxzz mentioned this pull request Nov 12, 2025

Allow .js extension #592

Closed

3 tasks

michaelfaith mentioned this pull request Nov 13, 2025

build: update package.json entries with explicit mjs / mts extensions JoshuaKGoldberg/eslint-plugin-package-json#1386

Merged

3 tasks

askoufis added a commit to seek-oss/vocab that referenced this pull request Nov 16, 2025

Update dist file extensions

f99d001

- See rolldown/tsdown#517

JoshuaKGoldberg mentioned this pull request Dec 2, 2025

feat: bumped most packages to latest as of Dec 2nd, 2025 JoshuaKGoldberg/create-typescript-app#2288

Merged

3 tasks

sadeghbarati mentioned this pull request Dec 8, 2025

chore: set tsdown fixedExtension: false to have .js output instead of .mjs antfu/eslint-config#787

Closed

Uh oh!

feat!: defaults fixedExtension to true when platform is node #517

feat!: defaults fixedExtension to true when platform is node #517

Conversation

sxzz commented Sep 28, 2025 • edited Loading Uh oh! There was an error while loading. Please reload this page.

Uh oh!

Description

Linked Issues

Additional context

Uh oh!

netlify bot commented Sep 28, 2025 • edited Loading Uh oh! There was an error while loading. Please reload this page.

Uh oh!

✅ Deploy Preview for tsdown ready!

Uh oh!

pkg-pr-new bot commented Sep 28, 2025 • edited Loading Uh oh! There was an error while loading. Please reload this page.

Uh oh!

Uh oh!

Uh oh!

RobinTail commented Nov 4, 2025

Uh oh!

sxzz commented Nov 4, 2025

Uh oh!

silverwind commented Nov 5, 2025 • edited Loading Uh oh! There was an error while loading. Please reload this page.

Uh oh!

Uh oh!

kitschpatrol commented Nov 5, 2025 • edited Loading Uh oh! There was an error while loading. Please reload this page.

Uh oh!

Uh oh!

sxzz commented Nov 5, 2025

Uh oh!

kitschpatrol commented Nov 5, 2025

Uh oh!

molvqingtai commented Nov 11, 2025

Uh oh!

sxzz commented Nov 11, 2025

Uh oh!

NiklasDah commented Nov 14, 2025

Uh oh!

sxzz commented Nov 15, 2025

Uh oh!

DopamineDriven commented Nov 21, 2025

Uh oh!

silverwind commented Nov 21, 2025

Uh oh!

sxzz commented Nov 22, 2025

Uh oh!

Reviewers

Assignees

Labels

Projects

Milestone

Development

Uh oh!

8 participants

feat!: defaults `fixedExtension` to true when platform is `node` #517

feat!: defaults `fixedExtension` to true when platform is `node` #517

sxzz commented Sep 28, 2025 •

edited

Loading

netlify bot commented Sep 28, 2025 •

edited

Loading

pkg-pr-new bot commented Sep 28, 2025 •

edited

Loading

silverwind commented Nov 5, 2025 •

edited

Loading

kitschpatrol commented Nov 5, 2025 •

edited

Loading