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Use exports field with .mjs extension instead of "module": "dist/polished.esm.js" in package.json #649

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tkamenoko opened this issue Feb 24, 2024 · 0 comments · May be fixed by #650
Open

Use exports field with .mjs extension instead of "module": "dist/polished.esm.js" in package.json #649

tkamenoko opened this issue Feb 24, 2024 · 0 comments · May be fixed by #650
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@bhough
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unconfirmed bug

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@tkamenoko
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Summary

polished provides an esm export via module field in package.json . However, Node.js does not support module field. Using exports field and .mjs extension is recommended to provide cjs/esm dual package.

https://nodejs.org/api/packages.html#packagejson-and-file-extensions

Node.js uses type field and each file extension to decide file type. module field has no effect.

Example

This example shows what files are actually imported when importing packages. prettier has both cjs and mjs exports, and its main field value is "./index.cjs" .

// import-test.mjs
console.log(import.meta.resolve("polished"));
console.log(import.meta.resolve("prettier"));
node --experimental-import-meta-resolve ./import-test.mjs

Result:

file://path/to/workspace/node_modules/polished/dist/polished.cjs.js
file://path/to/workspace/node_modules/prettier/index.mjs

cjs is selected for polished while mjs is selected for prettier .
tkamenoko added a commit to tkamenoko/polished that referenced this issue Mar 21, 2024
@tkamenoko
build(package.json, rollup.config.js): fix esm build to meet Node.js …
51db107 
…standard

To meet Node.js standard, 2 things should be fixed:

* ESM file should use `.mjs` extention
instead of `.esm.js`.
* `module` field in `package.json` is not standard way of Node.js. Use
`exports` field instead.

fix styled-components#649
@tkamenoko tkamenoko linked a pull request Mar 25, 2024 that will close this issue
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@bhough bhough self-assigned this Mar 13, 2025
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build(esm): modify rollup.config.js and package.json for better ESM packaging tkamenoko/polished
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@bhough @tkamenoko