# Functions

<a id="createextension"></a>

##  createExtension

▸ **createExtension**(key: *`Uint8Array`*): `Uint8Array`

*Defined in [stream/createExtension.ts:7](https://github.com/polkadot-js/common/blob/db4b221/packages/trie-codec/src/stream/createExtension.ts#L7)*

**Parameters:**

| Name | Type |
| ------ | ------ |
| key | `Uint8Array` |

**Returns:** `Uint8Array`

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