In Node, require("quickselect") returns the function quickselect, but in Webpack, require("quickselect") returns a module { default: quickselect }. This means a quickselect dependent can’t be compatible with both environments without contortions.

$ echo 'console.log(require("quickselect"))' > src.js
$ npm i quickselect webpack webpack-cli
$ node src.js
[Function: quickselect]
$ npx webpack -d
$ node dist/main.js 
Object [Module] { default: [Getter] }

This is because Node is using pkg.main (quickselect.js) and Webpack is using pkg.module (index.js), and the two files do not provide compatible interfaces.

This problem is called out in the Rollup documentation:

Note: There are some tools such as Babel, TypeScript, Webpack, and @rollup/plugin-commonjs that are capable of resolving a CommonJS require(...) call with an ES module. If you are generating CommonJS output that is meant to be interchangeable with ESM output for those tools, you should always use named export mode. The reason is that most of those tools will by default return the namespace of an ES module on require where the default export is the .default property.

This was previously touched on in #6, but only in the context of the current quickselect in Webpack being incompatible with an old quickselect in Webpack (resolved by bumping the major version), not the current quickselect in Webpack being incompatible with the current quickselect in Node (still an issue).

Three potential solutions are:

• use named export mode, so require("quickselect").default would work everywhere; or
• add quickselect.default = quickselect for compatibility; or
• remove pkg.module.