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# resolve.extensions

- **Type:** `string[]`
- **Default:** `['.ts', '.tsx', '.mjs', '.js', '.jsx', '.json']`

Automatically resolve file extensions when importing modules. This means you can import files without explicitly writing their extensions.

For example, if importing `'./index'`, Rsbuild will try to resolve using the following order:

- `./index.ts`
- `./index.tsx`
- `./index.mjs`
- `./index.js`
- `./index.jsx`
- `./index.json`

:::tip
It is not recommended to omit `.vue` or other custom import extension names using `resolve.extensions`, as this may interfere IDE and type support.
:::

## Example

The value of `resolve.extensions` overrides the default value of Rsbuild:

```ts title="rsbuild.config.ts"
export default {
  resolve: {
    extensions: ['.ts', '.tsx', '.js'],
  },
};
```

## Rspack config

`resolve.extensions` is provided by Rspack, see [Rspack - resolve.extensions](https://rspack.rs/config/resolve#resolveextensions).

You can also configure it using [tools.rspack](/config/tools/rspack.md):

```ts title="rsbuild.config.ts"
export default {
  tools: {
    rspack: {
      resolve: {
        extensions: ['.ts', '.tsx', '.js'],
      },
    },
  },
};
```

The difference between them is how the configuration is merged.

`tools.rspack` merges the configuration arrays based on [rspack-merge](https://github.com/rstackjs/rspack-merge), which means `tools.rspack.resolve.extensions` will merge with the default value of Rsbuild, rather than overriding it.