Read and write files

Bun.file() creates a reference to a file. It does not read the contents immediately.

Create settings.json:

{
  "siteName": "Bun Notes",
  "itemsPerPage": 20
}

Read it with:

type Settings = {
  siteName: string
  itemsPerPage: number
}

const file = Bun.file('settings.json')
const settings = await file.json() as Settings

console.log(settings.siteName)

A BunFile follows the Web Blob interface. You can read it as text, JSON, bytes, an array buffer, or a stream.

Check whether a file exists before reading optional data:

const file = Bun.file('settings.json')

if (await file.exists()) {
  console.log(await file.text())
}

Write a file

Bun.write() accepts a destination and some data:

const settings = {
  siteName: 'Bun Notes',
  itemsPerPage: 30,
}

await Bun.write(
  'settings.json',
  JSON.stringify(settings, null, 2),
)

The returned promise resolves to the number of bytes written.

You can also copy one file into another:

await Bun.write('settings.backup.json', Bun.file('settings.json'))

Use node:fs for directory operations such as mkdir() and readdir(). Bun implements those Node.js APIs, while Bun.file() and Bun.write() cover the common file-content path.