Node --experimental-modules - Error: Cannot find module

Question

I am getting an error when trying to import a local file, though no problem when using npm packages.

server.js

import express from 'express'
import next from 'next'

import apis from './src/server/api'

api.js

export default {
  ello: 'bye',
  jamie: 'hey'
}

Starting app

node --experimental-modules --inspect server.js

Error

For help, see: https://nodejs.org/en/docs/inspector
(node:20153) ExperimentalWarning: The ESM module loader is experimental.
internal/modules/esm/default_resolve.js:59
  let url = moduleWrapResolve(specifier, parentURL);
            ^

Error: Cannot find module '/var/www/goldendemon.hutber.com/src/server/api' imported from /var/www/goldendemon.hutber.com/server.js
    at Loader.resolve [as _resolve] (internal/modules/esm/default_resolve.js:59:13)
    at Loader.resolve (internal/modules/esm/loader.js:70:33)
    at Loader.getModuleJob (internal/modules/esm/loader.js:143:40)
    at ModuleWrap.<anonymous> (internal/modules/esm/module_job.js:43:40)
    at link (internal/modules/esm/module_job.js:42:36) {
  code: 'ERR_MODULE_NOT_FOUND'
}

Answer 1

I'm answering my own question if anybody else has this problem.

It turns out in experimental mode you need to define the full path with extension. So I am trying to import index.js thinking it will know.

To fix it:

import express from 'express'
import next from 'next'
import api from './src/server/api/index.js'

Answer 2

on Node v12 you have 2 options:

1. Use type="module" in package.json, experimental modules and specify extensions with specifier-resolution like this:

   node --experimental-modules --es-module-specifier-resolution=node server.js
   

2. Don't use specifier-resolution, you'll have to specify the extension of your files every where.

Update (from comment), for Node v18:

node --experimental-specifier-resolution=node server.js

Answer 3

It should also work if you name your module file with a .mjs extension. Also, other ways to enable ESM are mentioned here.

Node.js will treat the following as ES modules when passed to node as the initial input, or when referenced by import statements within ES module code:

• Files ending in .mjs.

• Files ending in .js, or extensionless files, when the nearest parent package.json file contains a top-level field "type" with a value of "module".

• Strings passed in as an argument to --eval or --print, or piped to node via STDIN, with the flag --input-type=module.

Answer 4

Or do like I did and just use transpilation the minute your source code deals with ES style module imports or some other non-standard JavaScript code, (E.g. TypeScript) on Node. For reference see this quick bash script I wrote, saved as .script/run-it.sh inside of my Node project:

#!/bin/bash

script=$1
out_path==/tmp/$script-out.js
npx esbuild --platform=node --bundle --outfile=$out_path $script
node $out_path 

I added it as a run script in my package.json:

"scripts": {
    "test": "sst test",
    "start": "sst start",
    "build": "sst build",
    "deploy": "sst deploy",
    "remove": "sst remove",
    "run-it": "./.script/run-it.sh"
  },

And my target script (import-test.js), what I want to emit/transpile as JavaScript code:

import { default as myImport } from './lib/index.js'
console.log(myImport)

And now I run it:

$ npm run run-it ./import-test.js 

> [email protected] run-it /Users/jmquij0106/git/a-rebalancing-act
> ./.script/run-it.sh "./import-test.js"

[Function: main]

Bottomline is spare yourself the pain and just emit CommonJS compliant code whenever dealing with ES Modules on Node.js, see this comment/issue.