bun-types/docs/api/file.md

Type definitions and documentation for Bun, an incredibly fast JavaScript runtime

Bun.js has fast paths for common use cases that make Web APIs live up to the performance demands of servers and CLIs.

`Bun.file(path)` returns a [`Blob`](https://developer.mozilla.org/en-US/docs/Web/API/Blob) that represents a lazily-loaded file.

When you pass a file blob to `Bun.write`, Bun automatically uses a faster system call:

```js
const blob = Bun.file("input.txt");
await Bun.write("output.txt", blob);
```

On Linux, this uses the [`copy_file_range`](https://man7.org/linux/man-pages/man2/copy_file_range.2.html) syscall and on macOS, this becomes `clonefile` (or [`fcopyfile`](https://developer.apple.com/library/archive/documentation/System/Conceptual/ManPages_iPhoneOS/man3/copyfile.3.html)).

`Bun.write` also supports [`Response`](https://developer.mozilla.org/en-US/docs/Web/API/Response) objects. It automatically converts to a [`Blob`](https://developer.mozilla.org/en-US/docs/Web/API/Blob).

```js
// Eventually, this will stream the response to disk but today it buffers
await Bun.write("index.html", await fetch("https://example.com"));
```