CJS Default Export

Control how default exports are handled in CommonJS output.

Overview

The cjsDefault option improves compatibility when generating CommonJS modules. When enabled (default), modules with only a single default export use module.exports = ... instead of exports.default = ....

Type

cjsDefault?: boolean  // default: true

Basic Usage

Enabled (Default)

export default defineConfig({
  entry: ['src/index.ts'],
  format: ['cjs'],
  cjsDefault: true, // default behavior
});

Disabled

export default defineConfig({
  entry: ['src/index.ts'],
  format: ['cjs'],
  cjsDefault: false,
});

How It Works

With `cjsDefault: true` (Default)

When your module has only a single default export, tsdown transforms:

Source:

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

Generated CJS:

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

Generated Declaration:

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

This allows consumers to use const greet = require('your-module') directly.

With `cjsDefault: false`

The default export stays as exports.default:

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

Consumers need require('your-module').default.

When to Disable

When your module has both default and named exports
When you need consistent exports.default behavior
When consumers always use ESM imports

Tips

Leave enabled for most libraries (default true)
Disable if you have both default and named exports and need consistent behavior
Test CJS consumers to verify compatibility

Output Format - Module formats
Shims - ESM/CJS compatibility

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