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# Interface: UnderlyingSourceStartCallback<R\>

[internal](../modules/internal-10.md).UnderlyingSourceStartCallback

## Type parameters

| Name |
| :------ |
| `R` |

## Callable

### UnderlyingSourceStartCallback

▸ **UnderlyingSourceStartCallback**(`controller`): `any`

#### Parameters

| Name | Type |
| :------ | :------ |
| `controller` | [`ReadableStreamController`](../modules/internal-10.md#readablestreamcontroller)<`R`\> |

#### Returns

`any`

#### Defined in

docs-util/node_modules/typescript/lib/lib.dom.d.ts:26898