---
url: /reference/Function.transform.md
---
# Function: transform()

* **Exported from**: `rolldown/utils`
* **Type**: (`filename`: `string`, `sourceText`: `string`, `options?`: [`TransformOptions`](Interface.TransformOptions-1.md) | `null`, `cache?`: [`TsconfigCache`](Class.TsconfigCache.md) | `null`) => `Promise`<[`TransformResult`](TypeAlias.TransformResult-1.md)>
* **Experimental**

Transpile a JavaScript or TypeScript into a target ECMAScript version, asynchronously.

Note: This function can be slower than `transformSync` due to the overhead of spawning a thread.

## Parameters

### filename

`string`

The name of the file being transformed. If this is a
relative path, consider setting the [`TransformOptions#cwd`](Interface.TransformOptions-1.md#cwd) option.

### sourceText

`string`

The source code to transform.

### options?

[`TransformOptions`](Interface.TransformOptions-1.md) | `null`

The transform options including tsconfig and inputMap. See [`TransformOptions`](Interface.TransformOptions-1.md) for more information.

### cache?

[`TsconfigCache`](Class.TsconfigCache.md) | `null`

Optional tsconfig cache for reusing resolved tsconfig across multiple transforms.
Used when `options.tsconfig` is `true` or a path. For a path, construct the
cache with the same path.

## Returns

`Promise`<[`TransformResult`](TypeAlias.TransformResult-1.md)>

a promise that resolves to an object containing the transformed code,
source maps, and any errors that occurred during parsing or transformation.