> For AI agents: the complete documentation index is available at /llms.txt, the full documentation bundle is available at /llms-full.txt.

# output.module

- **Type:** `boolean`
- **Default:** `true` when `output.target` is `node`, otherwise `false`

Whether to output JavaScript files in ES modules format.

:::tip

- If you need to build JavaScript libraries in ESM format, we recommend using [Rslib](https://rslib.rs), which is an out-of-the-box library development tool built on top of Rsbuild.

:::

## Web applications

When building a web application, Rsbuild generates the output in the IIFE format by default.

If you want to output ES Modules instead, set `output.module` to `true`:

```ts title="rsbuild.config.ts"
export default {
  output: {
    module: true,
  },
};
```

:::tip
When `output.module` is enabled, Rsbuild automatically adds `type="module"` to the generated `<script>` tags, meaning [html.scriptLoading](/config/html/script-loading.md) is set to `module`.
:::

## Web Workers

When [output.target](/config/output/target.md) is `'web-worker'`, set `output.module` to `true` to output an ES module worker bundle, for example for runtimes that load workers with `type: 'module'`:

```ts title="rsbuild.config.ts"
export default {
  output: {
    target: 'web-worker',
    module: true,
  },
};
```

## Node.js applications

When building Node.js applications, Rsbuild outputs ES modules format by default. You can set `output.module` to `false` to output CommonJS format instead:

```ts title="rsbuild.config.ts"
export default {
  output: {
    target: 'node',
    module: false,
  },
};
```

### Running ESM bundles

Choose either of the following approaches to run ESM bundles in Node.js:

1. Set the `type` field in package.json to `'module'`:

```json title="package.json"
{
  "type": "module"
}
```

2. Change the output JavaScript file extension to `.mjs`:

```ts title="rsbuild.config.ts"
export default {
  output: {
    filename: {
      js: '[name].mjs',
    },
  },
};
```

## Version history

| Version | Changes                             |
| ------- | ----------------------------------- |
| v1.5.0  | Added this option                   |
| v1.6.0  | Support for `target: 'web'`         |
| v2.0.0  | Default to ESM for `target: 'node'` |