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# html.mountId

- **Type:** `string`
- **Default:** `'root'`

By default, the `root` element is included in the HTML template for component mounting. The element id can be modified through `mountId`.

```html
<body>
  <div id="root"></div>
</body>
```

## Example

Set the `id` to `app`:

```ts title="rsbuild.config.ts"
export default {
  html: {
    mountId: 'app',
  },
};
```

After compilation:

```html
<body>
  <div id="app"></div>
</body>
```

## Notes

### Update relevant code

After modifying `mountId`, if there is logic in your code to obtain the `root` root node, please update the corresponding value:

```tsx
import { createRoot } from 'react-dom/client';

const domNode = document.getElementById('root'); // [!code --]
const domNode = document.getElementById('app'); // [!code ++]

createRoot(domNode).render(<App />);
```

### Custom templates

If you've customized the HTML template, please make sure that the template contains `<div id="<%= mountId %>"></div>`, otherwise the `mountId` config will not take effect.