> ## Documentation Index
> Fetch the complete documentation index at: https://mintlify.com/supermacro/neverthrow/llms.txt
> Use this file to discover all available pages before exploring further.

# ResultAsync.map

> Transform the Ok value of a ResultAsync

## Overview

Maps a `ResultAsync<T, E>` to `ResultAsync<U, E>` by applying a function to the contained `Ok` value. The `Err` value is left untouched.

## Signature

```typescript theme={null}
class ResultAsync<T, E> {
  map<A>(f: (t: T) => A | Promise<A>): ResultAsync<A, E>
}
```

<ParamField path="f" type="(t: T) => A | Promise<A>" required>
  Function to transform the Ok value. Can return either a value or a Promise.
</ParamField>

**Returns:** `ResultAsync<A, E>` - A new ResultAsync with the transformed value

## Usage

### Basic transformation

```typescript theme={null}
import { okAsync } from 'neverthrow'

const result = await okAsync(5)
  .map(x => x * 2)
  .map(x => x.toString())

// result is Ok('10')
```

### Async transformation

```typescript theme={null}
import { ResultAsync } from 'neverthrow'

const fetchUser = (id: number): ResultAsync<User, Error> => {
  return ResultAsync.fromPromise(
    fetch(`/api/users/${id}`).then(r => r.json()),
    (e) => new Error('Fetch failed')
  )
}

const result = await fetchUser(123)
  .map(async user => {
    // Async transformation
    const enriched = await enrichUserData(user)
    return enriched
  })
  .map(user => user.name)
```

### Error handling

```typescript theme={null}
const result = await errAsync('Database error')
  .map(x => x * 2)
  .map(x => x.toString())

// map is never called, result is Err('Database error')
```

## Key characteristics

<Note>
  The mapping function can be either synchronous or asynchronous with no impact on the return type - both return `ResultAsync`.
</Note>

* **Short-circuits on Err**: If the ResultAsync is an Err, map is not executed
* **Type safety**: The transformed type is tracked through the chain
* **Async support**: Can handle both sync and async transformation functions

## Related

<CardGroup cols={2}>
  <Card title="mapErr" icon="triangle-exclamation" href="./map-err">
    Transform the error value
  </Card>

  <Card title="andThen" icon="link" href="./and-then">
    Chain operations that return Results
  </Card>
</CardGroup>