The non-standard `package.json` field `module` was used. This pointed to a faux ESM file (Uses ESM syntax, but has a `.js` file extension in a package which doesn’t specify `"type": "module"`.

ESM support was fixed by using the `.mjs` file extension for the ESM export and defining a proper `exports` field in `package.json.

The types reflected a package that has the `module.exports.default` field. This was incorrect. The CommonJS types have now been fixed to use `export =`, which is the correct way to type modules that use `module.exports` assignments.

Additional types were added for ESM support.

This fixes the following issues that have previously been closed without a solution.

Closes #27 Closes #43 Closes #50

To try this locally, try running the following in the Node.js repl from the package root:

``` $ node Welcome to Node.js v18.12.0. Type ".help" for more information. > require('clsx') <ref *1> [Function: r] { clsx: [Circular *1] } > await import('clsx') [Module: null prototype] { clsx: [Function: clsx], default: [Function: clsx] }

```

clsx already works with `require` and `import` and `import()` statements:

<img width="591" alt="Screen Shot 2022-11-01 at 10 50 44 AM" src="https://user-images.githubusercontent.com/5855893/199303822-bf8571c1-3c29-478b-a419-db9549b8ebe7.png">

The rest of this PR is adding breaking changes:

1. Adding `exports` map (always is), and is unnecessary since there's only 1 file/entry point 2. The `module` change to a `.mjs` extension breaks most older bundler versions (rollup/webpack) since it changes how they will handle module resolution for the rest of the tree. (Dark, early ESM days) 3. Using `.d.mts` is strictly unnecessary & binds you to a minimum TS version for no reason at all, especially given the `export = clsx` contents.

> clsx already works with `require` and `import` and `import()` statements: > > <img alt="Screen Shot 2022-11-01 at 10 50 44 AM" width="591" src="https://user-images.githubusercontent.com/5855893/199303822-bf8571c1-3c29-478b-a419-db9549b8ebe7.png">

Yes, commonjs files can be imported from ESM. The fact that there’s a faux ESM file and TypeScript type definitions describe a default export instead of `export =`, gave the impression the intended behaviour was to support actual ESM. A lot of packages have there type definitions wrong, which has become more apparent since the release of TypeScript 4.7.

> The rest of this PR is adding breaking changes: > > 1. Adding `exports` map (always is), and is unnecessary since there's only 1 file/entry point

Whether or not this is breaking is subjective. This disallows people to import subpaths from the package. I would consider that unintemded behaviour and therefor not consider this to be a breaking change. However, since you’re the maintainer, your view on this counts.

Adding an `exports` map isn’t unnecessary when adding native ESM support. However, if you’re not interested, then indeed the `exports` map is unnecessary.

> 2. The `module` change to a `.mjs` extension breaks most older bundler versions (rollup/webpack) since it changes how they will handle module resolution for the rest of the tree. (Dark, early ESM days)

I wasn’t aware of this. It is possible to support both though (but not without `exports`).

> 3. Using `.d.mts` is strictly unnecessary & binds you to a minimum TS version for no reason at all, especially given the `export = clsx` contents.

This isn’t true. This file is only used by the `node16` / `nodenext` module resolution to support native ESM. The `index.d.ts` is still used by other module resolutions as it always was.

> Whether or not this is breaking is subjective.

Node 13-13.7 had a different exports map specification. The finalized spec throws an error in these versions and there’s no way to support both. Thus adding sny exports map is breaking as it has to be done with a minimum version bump.

> This isn’t true.

Yes it is. You can define “types” for exports to a standard .d.ts file, even for nodenext/node16 mode. The mts extension is just to force/guarantee that TS treats the file as ESM, similar to .mjs even tho .js can also contain ESM. In fact, mts is a front/stand-in for would-be-emitted .mjs files.

@lukeed I kindly ask you to reconsider this or equivalent PR. [Incorrect types](https://arethetypeswrong.github.io/?p=clsx%401.2.1) are causing us a ton of problems which may force us to replace clsx with [correctly typed](https://arethetypeswrong.github.io/?p=classnames%402.3.2) classnames in many repositories and that would be a huge bummer.

I'll cut a new major version that includes an "exports" map

## [Codecov](https://app.codecov.io/gh/lukeed/clsx/pull/57?src=pr&el=h1&utm_medium=referral&utm_source=github&utm_content=comment&utm_campaign=pr+comments&utm_term=Luke+Edwards) Report Patch and project coverage have no change. > Comparison is base [(`6da37d6`)](https://app.codecov.io/gh/lukeed/clsx/commit/6da37d67472ea9eb177a4ea9a9fa2f3f4a3c445e?el=desc&utm_medium=referral&utm_source=github&utm_content=comment&utm_campaign=pr+comments&utm_term=Luke+Edwards) 100.00% compared to head [(`40a074e`)](https://app.codecov.io/gh/lukeed/clsx/pull/57?src=pr&el=desc&utm_medium=referral&utm_source=github&utm_content=comment&utm_campaign=pr+comments&utm_term=Luke+Edwards) 100.00%.

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<details><summary>Additional details and impacted files</summary>

```diff @@ Coverage Diff @@ ## master #57 +/- ## ========================================= Coverage 100.00% 100.00% ========================================= Files 1 1 Lines 22 22 ========================================= Hits 22 22 ```

</details>

[:umbrella: View full report in Codecov by Sentry](https://app.codecov.io/gh/lukeed/clsx/pull/57?src=pr&el=continue&utm_medium=referral&utm_source=github&utm_content=comment&utm_campaign=pr+comments&utm_term=Luke+Edwards). :loudspeaker: Do you have feedback about the report comment? [Let us know in this issue](https://about.codecov.io/codecov-pr-comment-feedback/?utm_medium=referral&utm_source=github&utm_content=comment&utm_campaign=pr+comments&utm_term=Luke+Edwards).

Thanks for merging and releasing this! ❤️

Thank you for the PR & patience!