---
url: /reference/api/TypeAlias.NoExternalFn.md
---
# Type Alias: NoExternalFn

```ts
type NoExternalFn = (id, importer) => boolean | null | undefined | void
```

Defined in: [src/features/deps.ts:35](https://github.com/rolldown/tsdown/blob/46cacd570c8ed72441c87458d9bb796b41d3b27f/src/features/deps.ts#L35)

## Parameters

### id

`string`

### importer

`string` | `undefined`

## Returns

`boolean` | `null` | `undefined` | `void`