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"));
```