How to resolve "Failed to resolve entry for package fs" in SvelteKit / Vite build?

11 nov 2023

The quick answer:

Replace the first snippet with the second.

import fs from 'fs';

import fs from 'node:fs';

The issue, and things I’ve tried:

I was trying to use the fs module in a server load function in a SvelteKit project, and I was getting the following error:

[commonjs–resolver] Failed to resolve entry for package “fs”. The package may have incorrect main/module/exports specified in its package.json. error during build: Error: Failed to resolve entry for package “fs”. The package may have incorrect main/module/exports specified in its package.json.

Of course, everything worked perfectly fine in dev and VSCode was throwing no errors at me, but the build step was failing in spite of that.

Some steps I tried:

npm install fs. I didn’t really expect it to work, but it was the first thing I tried. It didn’t work.
npm install @types/node. I thought maybe it was a typing issue. It wasn’t.

Aliasing `fs` to `rollup-plugin-node-builtins`

So I turned to the internet, they could probably help me! (they could not).

this issue on the Nuxt/vite repo suggests aliasing fs to require.resolve('rollup-plugin-node-builtins'),. Even attempting that was troublesome, because this is the modern day SvelteKit, not the SvelteKit of old — no more require!

Like a silly goose, the first thing I tried was await import.meta.resolve, which does not actually exist. Okay, next guess.

I turned to the internet to find the ES6 replacement of require.resolve. They suggested I just use createRequire, which would allow you to use require in an ES6 module. I gave it a shot, and things changed! All of the sudden the fs error was gone, but I was getting some new issues:

node:internal/event_target:1012 process.nextTick (() => ());

^

ReferenceError Error: require is not defined in ES module scope, you can use import instead

This file is being treated as an ES module because it has a ‘.js’ file extension and ‘/Users/jip/Desktop/elliesblog/package.json’ contains “type”: “module”. To treat it as a CommonJS script, rename it to use the ‘.cjs’ file extension.

Wonderful — the build step was now injecting CommonJS into my ES6 module, which was causing all sorts of issues.

I tried logging the result of the require.resolve to inject it directly into the alias rather than using createRequire. The logic was that perhaps the createRequire was telling the build step to use CommonJS, breaking the whole thing? I replaced require.resolve("rollup-plugin-node-builtins") with ./node_modules/rollup-plugin-node-builtins/dist/rollup-plugin-node-builtins.cjs.js and absolutely nothing changed. I was still getting the same error. Even replacing the .cjs with .es6 (the module exports both) changed nothing.

Finally.

In a GitHub issue only vaguely related I saw that somebody was importing node:child_process rather than just child_process. I figured “to hell with it” and tried importing node:fs rather than just fs, which did the trick.

Why didn’t Node just import node:fs in the build step rather than this fantasy fs? What other fs is there? These are questions not even Jonathan Frakes can answer on his show. I’m just happy it worked.