Running code

Every exec call takes JavaScript module source, not a shell command. The durable object builds a module graph from it, starts a fresh Dynamic Worker, and evaluates the module there. Nothing is shared between calls.

The shape of a module

Put the work inside the default export, and return what you want back:

import { readdir, readFile } from "node:fs/promises";

export default async function (input) {
  const names = await readdir(input.dir);
  const first = await readFile(`${input.dir}/${names[0]}`, "utf8");
  return { count: names.length, first };
}

• The default export gets the call's input value.
• Its return value comes back as the result's value. It must be JSON-compatible.
• console.log and console.info go to standard output. console.warn and console.error go to standard error.
• A thrown error ends the run with a non-zero exit code and the message on standard error. So does a promise that rejects with nothing handling it, so await everything you start.
• Code at the top level runs before the call is set up. A file read or a fetch there fails with Disallowed operation called within global scope. Imports at the top are fine.

What code can import

• node:fs/promises (also node:fs): the workspace's files. The supported calls are readFile, writeFile, mkdir, rm, readdir, stat, lstat, readlink, symlink, chmod and access. All of them are async.
• Node.js built-ins such as node:path, node:crypto, node:zlib and node:buffer, with subpaths like node:stream/promises. Bare names such as path work too.
• Relative imports resolve from cwd in the workspace, so you can write a helper module with one call and import it in the next.
• There is no node_modules lookup and no npm. Beyond the modules above, only the ones the host configures are available.

Limits

• No direct network access. fetch to the internet fails.
• Each run has a time limit: one minute by default, three at most.
• Source, input and the returned value are capped at 1 MiB each.

Files

• cwd defaults to /workspace.
• File operations go straight to the durable object's storage. There's nothing to sync, so a write is visible to the next call right away.
• /workspace/r2 is a read-only copy of an R2 bucket.
• /workspace/.agents/skills (where this file lives) is a read-only copy of files shipped with the Worker. Writing under either one fails with EROFS.