# Function: map()

> 

> **map**\<`TValueBefore`, `TError`, `TValueAfter`\>(`project`): `OperatorFunction`\<`TValueBefore`, `TError`, `TValueAfter`, `TError`\>

Defined in: [packages/server/src/observable/operators.ts:10](https://github.com/trpc/trpc/blob/7c907acfd8b31929214792e3b8c2ad7a8ac72563/packages/server/src/observable/operators.ts#L10)

Maps each value with `project`.

## Type Parameters

| Type Parameter |
| ------ |
| `TValueBefore` |
| `TError` |
| `TValueAfter` |

## Parameters

| Parameter | Type |
| ------ | ------ |
| `project` | (`value`, `index`) => `TValueAfter` |

## Returns

`OperatorFunction`\<`TValueBefore`, `TError`, `TValueAfter`, `TError`\>