Why does my Cloudflare Worker still throw “No such module ‘node:fs’ / ‘fs’” even with nodejs_compat enabled?

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Summary

The issue of Cloudflare Workers throwing a “No such module ‘node:fs’ / ‘fs'” error even with nodejs_compat enabled is a common problem encountered when trying to use Node.js libraries inside a Cloudflare Worker. This error occurs despite following the recommended configurations, such as setting a recent compatibility_date and enabling nodejs_compat in the wrangler.toml file.

Root Cause

The root cause of this issue is due to the following reasons:

  • Limited File System Access: Cloudflare Workers have limited access to the file system, and the node:fs module is not fully supported.
  • Virtual File System: The file system in Cloudflare Workers is virtual and ephemeral, which means that files are not persisted across requests.
  • Module Resolution: The node:fs module is not resolved correctly, even with nodejs_compat enabled.

Why This Happens in Real Systems

This issue occurs in real systems because:

  • Cloudflare Workers are designed to be lightweight and stateless, which limits their ability to access the file system.
  • Node.js libraries that rely on the fs module are not compatible with Cloudflare Workers out of the box.
  • Configuration issues, such as incorrect compatibility_date or missing compatibility_flags, can also contribute to this problem.

Real-World Impact

The real-world impact of this issue includes:

  • Failed Deployments: Cloudflare Workers may fail to deploy due to the “No such module ‘node:fs’ / ‘fs'” error.
  • Limited Functionality: The inability to use Node.js libraries that rely on the fs module limits the functionality of Cloudflare Workers.
  • Increased Development Time: Developers may spend more time troubleshooting and finding workarounds for this issue.

Example or Code

// This code will throw an error in a Cloudflare Worker
import fs from 'node:fs';

export default {
  async fetch() {
    const txt = fs.readFileSync('./foo.txt', 'utf8');
    return new Response(txt);
  },
};

How Senior Engineers Fix It

Senior engineers fix this issue by:

  • Using Alternative Libraries: They use alternative libraries that are compatible with Cloudflare Workers, such as fetch or URL.
  • Implementing Workarounds: They implement workarounds, such as using Blob or ArrayBuffer to read and write files.
  • Configuring Correctly: They ensure that the wrangler.toml file is configured correctly, with the correct compatibility_date and compatibility_flags.

Why Juniors Miss It

Juniors may miss this issue because:

  • Lack of Experience: They may not have experience working with Cloudflare Workers or Node.js libraries.
  • Insufficient Documentation: They may not have read the documentation carefully, or may not understand the limitations of Cloudflare Workers.
  • Overreliance on nodejs_compat: They may rely too heavily on nodejs_compat to enable Node.js functionality, without understanding the underlying limitations.