avisek / rollup-patch-seamless-default-export

Rollup patch for adding `module.exports = defaultExport`

A patch for rollup that allows you to consume default and named exports from your library like this,

// Default export
const lib = require('your-library')
lib('Hello') // <-- instead of using `.default` property

// Named exports
const { namedExport1, namedExport2 } = lib

// One liner syntex. This is also supported.
const { default: defaultExport, namedExport1, namedExport2 } = require('your-library')

Your library (sample code for context):

export default function defaultExport(msg) {
  console.log(`${msg} from default export`)
}

export const namedExport1 = 'named export 1'
export const namedExport2 = 'named export 2'

Why?

For syntactic sugar.

// Without this patch if you transform ESM to CJS
// and have both `default` and `named` exports in a single file,
// whatever you export as default will get assigned to
// `module.exports.default` instead of `module.exports`.
// So if somebody `require()`s your module they'll have to
// access your default export like this,
const lib = require('your-library').default // <-- it looks bad
//                                  ^^^^^^^

Read this and this thread for more context.

How to use the patch? _{^{(pnpm version)}}

Download and include the patch file

  .
  ├── ...
+ ├── patches
+ │   └── rollup+3.29.4.patch
  └── package.json

Add postinstall script in package.json

  ...
  "scripts": {
    "build": "rollup -c",
+   "postinstall": "patch-package"
  },
  "devDependencies": {
    "rollup": "^3.29.4"   <-- Make sure rollup's version is the same as the patch
  }
  ...

Install patch-package

npm install patch-package --save-dev

Done.

How does it work?

It modifies rollup's output like this,

+ exports = module.exports = defaultExport;
+ exports.default = defaultExport;
  exports.namedExport1 = namedExport1;
  exports.namedExport2 = namedExport2;
- exports.default = defaultExport;

Caveats

You can not use primitive type values (e.g. string, number, boolean) as your defaut export. If you do, then your named exports will not work.