File I/O in TypeScript Golem Agents

Overview

Golem TypeScript agents run in a QuickJS-based WASM runtime that provides node:fs and node:fs/promises modules for filesystem operations. Use these to read files provisioned via the Initial File System (IFS) or to write temporary data.

To provision files into an agent’s filesystem, See the golem-add-initial-files guide. To understand the full runtime environment, See the golem-js-runtime guide.

Reading Files

Synchronous


import * as fs from 'node:fs';
 
const content = fs.readFileSync('/data/config.json', 'utf-8');

Asynchronous


import * as fsp from 'node:fs/promises';
 
const content = await fsp.readFile('/data/config.json', 'utf-8');

Reading Binary Files


import * as fs from 'node:fs';
 
const buffer = fs.readFileSync('/data/image.png');
// buffer is a Buffer (Uint8Array subclass)

Writing Files

Only files provisioned with read-write permission (or files in non-provisioned paths) can be written to.


import * as fs from 'node:fs';
 
fs.writeFileSync('/tmp/output.txt', 'Hello, world!');

Asynchronous


import * as fsp from 'node:fs/promises';
 
await fsp.writeFile('/tmp/output.json', JSON.stringify(data));

Checking File Existence


import * as fs from 'node:fs';
 
if (fs.existsSync('/data/config.json')) {
  const content = fs.readFileSync('/data/config.json', 'utf-8');
}

Listing Directories


import * as fs from 'node:fs';
 
const files = fs.readdirSync('/data');
// files is string[]

Complete Agent Example


import { BaseAgent, agent } from '@golemcloud/golem-ts-sdk';
import * as fs from 'node:fs';
 
@agent()
class FileReaderAgent extends BaseAgent {
  constructor(readonly name: string) {
    super();
  }
 
  async readGreeting(): Promise<string> {
    const content = fs.readFileSync('/data/greeting.txt', 'utf-8');
    return content.trim();
  }
 
  async writeLog(message: string): Promise<void> {
    fs.appendFileSync('/tmp/agent.log', message + '\n');
  }
}

Key Constraints

Use node:fs or node:fs/promises — they are fully supported in the QuickJS runtime
Files provisioned via golem-add-initial-files with read-only permission cannot be written to
The filesystem is per-agent-instance — each agent has its own isolated filesystem
File changes within an agent are persistent across invocations (durable state)