The Bun.file() function accepts a path and returns a BunFile instance. The BunFile class extends Blob and allows you to lazily read the file in a variety of formats. Use .arrayBuffer() to read the file as an ArrayBuffer.
const path = "/path/to/package.json";
const file = Bun.file(path);
const buffer = await file.arrayBuffer();
The binary content in the ArrayBuffer can then be read as a typed array, such as Uint8Array.
const buffer = await file.arrayBuffer();
const bytes = new Uint8Array(buffer);
bytes[0];
bytes.length;
Refer to the Typed arrays docs for more information on working with typed arrays in Bun.