CJS Default Export

The cjsDefault option helps improve compatibility when generating CommonJS (CJS) entry modules. This option is enabled by default.

How It Works

When an explicit entry module has only a single default export and the output format is set to CJS, tsdown will automatically transform:

• export default ... into module.exports = ... in the generated JavaScript file.

For TypeScript declaration files (.d.ts), it will transform:

• export default ... into export = ...

This ensures that consumers using CommonJS require syntax (require('your-module')) will receive the default export directly, improving interoperability with tools and environments that expect this behavior.

NOTE

cjsDefault only applies to explicit entry modules. In unbundle mode, imported modules that are emitted as non-entry chunks keep named CJS exports such as exports.default. CJS is considered legacy and is supported in maintenance-only mode, so this behavior will not be extended to non-entry chunks.

If every source module is intended to be consumed independently, include all of them as entries:

import { defineConfig } from 'tsdown'

export default defineConfig({
  entry: ['src/**/*.ts'],
  root: 'src',
  format: 'cjs',
  unbundle: true,
})

Example

Source Module:

// src/index.ts
export default function greet() {
  console.log('Hello, world!')
}

Generated CJS Output:

// dist/index.cjs
function greet() {
  console.log('Hello, world!')
}
module.exports = greet

Generated Declaration File:

// dist/index.d.cts
declare function greet(): void
export = greet