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 .