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agent-skills/skills/tsdown/references/option-cjs-default.md
Jason Woltje f5792c40be feat: Complete fleet — 94 skills across 10+ domains
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Co-Authored-By: Claude Opus 4.6 <noreply@anthropic.com>
2026-02-16 16:27:42 -06:00

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# 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
```ts
cjsDefault?: boolean // default: true
```
## Basic Usage
### Enabled (Default)
```ts
export default defineConfig({
entry: ['src/index.ts'],
format: ['cjs'],
cjsDefault: true, // default behavior
})
```
### Disabled
```ts
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:**
```ts
// src/index.ts
export default function greet() {
console.log('Hello, world!')
}
```
**Generated CJS:**
```js
// dist/index.cjs
function greet() {
console.log('Hello, world!')
}
module.exports = greet
```
**Generated Declaration:**
```ts
// 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`:
```js
// 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
1. **Leave enabled** for most libraries (default `true`)
2. **Disable** if you have both default and named exports and need consistent behavior
3. **Test CJS consumers** to verify compatibility
## Related Options
- [Output Format](option-output-format.md) - Module formats
- [Shims](option-shims.md) - ESM/CJS compatibility