Reading & Writing Files in Bun

From the Bun cheat sheet · File I/O · verified Jul 2026

Reading & Writing Files

Fast file operations with Bun.file() and Bun.write()

typescript

// Read a file
const file = Bun.file("data.json");
const text = await file.text();
const json = await file.json();

// Write a file
await Bun.write("output.txt", "Hello World");
await Bun.write("data.json", JSON.stringify({ ok: true }));

💡 Bun.file() is lazy — it only reads from disk when you call .text(), .json(), etc.

⚡ Bun.write() is 10x faster than Node fs.writeFileSync — uses optimized system calls

📌 Pass a Bun.file() or fetch Response directly to Bun.write() for zero-copy operations

🟢 Use file.writer() for incremental writes like logging — flush() ensures data persists

filereadwriteio

Back to the full Bun cheat sheet