rolldown-plugin-require-cjs

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Transform ESM imports to CJS requires when the imported module is pure CJS.

Why?

Some packages only provide CJS builds (e.g., typescript, @babel/parser), and importing them using ESM syntax increases Node's cjs-module-lexer overhead. This plugin converts ESM imports to CJS requires for such pure CJS packages, allowing Node to skip the cjs-module-lexer step and improve performance.

If performance is insignificant for your project, please do not use this plugin, as it introduces additional complexity and maintenance overhead.

See more: https://x.com/sanxiaozhizi/status/1968580207322808812

Appeal

We encourage the JavaScript ecosystem to continue its transition toward ESM. If you maintain a package that is still CJS-only, please consider offering an ESM build or migrating fully to ESM. Doing so will reduce reliance on plugins like this one and enhance the overall performance of the ecosystem.

Install

``bash
npm i rolldown-plugin-require-cjs
`

Options

`ts
export interface Options {
include?: Array | string | RegExp
exclude?: Array | string | RegExp
order?: 'pre' | 'post' | undefined
/**
* A function to determine whether a module should be transformed.
* Return true to force transformation, false to skip transformation,
* or undefined to let the plugin decide automatically.
*/
shouldTransform?: string[] | TransformFn
/**
* Whether to transform Node.js built-in modules (e.g., fs, path)
* to process.getBuiltinModule() calls, which has the best performance.
*
* Note: process.getBuiltinModule is available since Node.js 20.16.0 and 22.3.0.
*/
builtinNodeModules?: boolean
}

/**
* @returns A boolean or a promise that resolves to a boolean,
* or undefined to let the plugin decide automatically.
*/
export type TransformFn = (
/**
* The module ID (path) being imported.
*/
id: string,
/**
* The module ID (path) of the importer.
*/
importer: string,
) => Awaitable
`

Example

`ts
RequireCJS({
shouldTransform(id, importer) {
// Force transformation for specific dependencies
if (id === 'typescript') return true
// Skip transformation for specific dependencies
if (id === 'esm-only') return false
// Auto-detect for other dependencies
return undefined
},
})
``

Sponsors

License

MIT License © 2025-PRESENT Kevin Deng

[npm-version-src]: https://img.shields.io/npm/v/rolldown-plugin-require-cjs.svg
[npm-version-href]: https://npmjs.com/package/rolldown-plugin-require-cjs
[npm-downloads-src]: https://img.shields.io/npm/dm/rolldown-plugin-require-cjs
[npm-downloads-href]: https://www.npmcharts.com/compare/rolldown-plugin-require-cjs?interval=30
[unit-test-src]: https://github.com/sxzz/rolldown-plugin-require-cjs/actions/workflows/unit-test.yml/badge.svg
[unit-test-href]: https://github.com/sxzz/rolldown-plugin-require-cjs/actions/workflows/unit-test.yml