FileHandle.writer method | Node.js fs/promises module | Bun

Return a node:stream/iter writer backed by this file handle.

The writer supports both Symbol.asyncDispose and Symbol.dispose:

The writeSync() and writevSync() methods enable the try-sync fast path used by stream/iter pipeTo(). When the reader's chunk size matches the writer's chunkSize, all writes in a pipeTo() pipeline complete synchronously with zero promise overhead.

This function is only available when the --experimental-stream-iter flag is enabled.

import { open } from 'node:fs/promises';
import { from, pipeTo } from 'node:stream/iter';
import { compressGzip } from 'node:zlib/iter';

// Async pipeline
const fh = await open('output.gz', 'w');
await pipeTo(from('Hello!'), compressGzip(), fh.writer({ autoClose: true }));

// Sync pipeline with limit
const src = await open('input.txt', 'r');
const dst = await open('output.txt', 'w');
const w = dst.writer({ limit: 1024 * 1024 }); // Max 1 MB
await pipeTo(src.pull({ autoClose: true }), w);
await w.end();
await dst.close();

Close the file handle when the writer ends or fails.

Maximum chunk size in bytes for synchronous write operations. Writes larger than this threshold fall back to async I/O. Set this to match the reader's chunkSize for optimal pipeTo() performance.

Maximum number of bytes the writer will accept. Async writes (write(), writev()) that would exceed the limit reject with ERR_OUT_OF_RANGE. Sync writes (writeSync(), writevSync()) return false.

Byte offset to start writing at. When specified, writes use explicit positioning.