Setting a custom working directory for a worker_thread Worker

[TimDaub]

process.chdir allows changing node's working directory. When using a Worker from worker_threads it is not available though.

  TypeError {
    code: 'ERR_WORKER_UNSUPPORTED_OPERATION',
    message: 'process.chdir() is not supported in workers',
  }

How can I customize a worker thread's directory e.g. upon startup?

[doxybox]

A worker_threads.Worker cannot have an independent process working directory. Workers share a process, and Node explicitly disables process.chdir() in workers. Moving the worker script to another directory does not change the working directory used by relative filesystem paths.

If you control the file operations, pass a base directory and resolve paths against it instead:

// main.mjs
import { Worker } from 'node:worker_threads';
import { fileURLToPath } from 'node:url';

const worker = new Worker(new URL('./worker.mjs', import.meta.url), {
  workerData: {
    baseDir: fileURLToPath(new URL('./data/', import.meta.url)),
  },
});
worker.on('message', console.log);
worker.on('error', (error) => {
  console.error(error);
  process.exitCode = 1;
});

// worker.mjs
import { parentPort, workerData } from 'node:worker_threads';
import { readFile } from 'node:fs/promises';
import { resolve } from 'node:path';

const text = await readFile(resolve(workerData.baseDir, 'input.txt'), 'utf8');
parentPort.postMessage(text);

Create data/input.txt next to main.mjs, then run node main.mjs. This selects a base directory for those explicit file operations; it does not change process.cwd() or automatically redirect a library's relative file access.

If a library requires its own actual working directory, run it in a child process instead:

import { fork } from 'node:child_process';

const child = fork(new URL('./child.mjs', import.meta.url), [], {
  cwd: new URL('./data/', import.meta.url),
});
child.on('error', console.error);

Here child.mjs is your separate Node entry point, and data/ must exist. The child gets that working directory without changing the parent's.

References: Worker limitations, fork's cwd option.

Locally verified on Windows with Node v25.3.0: explicit-path reads in a worker succeeded, worker process.chdir() raised ERR_WORKER_UNSUPPORTED_OPERATION, and a forked child read a relative file from its own cwd while the parent's cwd stayed unchanged. Drafted and tested with AI assistance.