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url: /reference/TypeAlias.ExternalOptionFunction.md
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# Type Alias: ExternalOptionFunction

* **Type**: (`id`, `parentId`, `isResolved`) => `NullValue`<`boolean`>

## Parameters

### id

`string`

The id of the module being checked.

### parentId

`string` | `undefined`

The id of the module importing the id being checked.

### isResolved

`boolean`

Whether the id has been resolved.

## Returns

`NullValue`<`boolean`>

Whether the module should be treated as external.