[BUG] ExperimentalWarning: Support for loading ES Module in require() is an experimental feature and might change at any time

[alexsch01]

Is there an existing issue for this?

• I have searched the existing issues

This issue exists in the latest npm version

• I am using the latest npm

Current Behavior

When installing any package with Node.js v23.0.0 and npm v10.9.0, I get the following warning

(node:10424) ExperimentalWarning: Support for loading ES Module in require() is an experimental feature and might change at any time
(Use `node --trace-warnings ...` to show where the warning was created)

Expected Behavior

No response

Steps To Reproduce

No response

Environment

• npm: 10.9.0
• Node.js: 23.0.0
• OS Name: Windows 10 22H2
• npm config: default

; node bin location = C:\Program Files\nodejs\node.exe
; node version = v23.0.0
; npm local prefix = C:\Users\$USER\Downloads\test
; npm version = 10.9.0
; cwd = C:\Users\$USER\Downloads\test
; HOME = C:\Users\$USER
; Run `npm config ls -l` to show all defaults.

[shadowspawn]

This is triggered by the experimental --experimental-require-module flag being made the default behaviour in Node.js 23. Related links:

• debug causes npm to always issue an experimental ESM warning in node 23 debug-js/debug#975
• 2024-10-16, Version 23.0.0 (Current) nodejs/node#55338 (comment)
• module: unflag --experimental-require-module nodejs/node#55085

[MikeMcC399]

It's not necessary to install anything with npm to provoke the ExperimentalWarning.

For example, even with no npm modules installed, executing npm view npm version results in the ExperimentalWarning:

$ npm view npm version
(node:5212) ExperimentalWarning: Support for loading ES Module in require() is an experimental feature and might change at any time
(Use `node --trace-warnings ...` to show where the warning was created)
10.9.0

Ubuntu 24.04.1 LTS
Node.js v23.0.0
npm 10.9.0 (latest)

Same ExperimentalWarning for many other CLI commands from https://docs.npmjs.com/cli/v10/commands:

npm audit
npm ci
npm doctor
npm init
npm install
npm install-ci-test
npm ls
npm outdated
npm prune
npm repo
npm show
... etc

[MikeMcC399]

• See also discussion in Can we supress the new experimental warning from the new default require(esm) setting? nodejs/node#55417

[MikeMcC399]

Setting the environment variable NODE_OPTIONS='--trace-warnings' produces some trace output.

$ NODE_OPTIONS='--trace-warnings' npm view npm view
(node:6610) ExperimentalWarning: Support for loading ES Module in require() is an experimental feature and might change at any time
    at emitExperimentalWarning (node:internal/util:273:11)
    at loadESMFromCJS (node:internal/modules/cjs/loader:1388:5)
    at Module._compile (node:internal/modules/cjs/loader:1525:5)
    at Object..js (node:internal/modules/cjs/loader:1680:16)
    at Module.load (node:internal/modules/cjs/loader:1328:32)
    at Function._load (node:internal/modules/cjs/loader:1138:12)
    at TracingChannel.traceSync (node:diagnostics_channel:315:14)
    at wrapModuleLoad (node:internal/modules/cjs/loader:218:24)
    at Module.require (node:internal/modules/cjs/loader:1350:12)
    at require (node:internal/modules/helpers:138:16)

[avivkeller]

FYI the ESM being require()d is supports-color.

[MikeMcC399]

@redyetidev

FYI the ESM being require()d is supports-color.

You're right!

cli/package.json

Line 113 in 780afc5

"supports-color": "^9.4.0",

where supports-color@9.0.0 and above is pure ESM

• As identified by @ljharb in debug causes npm to always issue an experimental ESM warning in node 23 debug-js/debug#975 and relayed above by @shadowspawn , debug is using the following code to check on the availability of supports-color.

const supportsColor = require('supports-color'); 

where debug is effectively allowing an ESM version of supports-color to be installed and used:

  "peerDependenciesMeta": {
    "supports-color": {
      "optional": true
    }

So I guess the underlying issue debug-js/debug#975 needs to be resolved by debug.

[MikeMcC399]

• To test, I downgraded to npm@9.7.1 prior to PR fix: better color support detection #6556 in npm@9.7.2

npm install npm@9.7.1 -g

and there was no more warning under Node.js v23.0.0 from

npm view npm version

[MikeMcC399]

Under Node.js v23.1.0 the warning provides additional debugging information which confirms the previous analysis:

$ npm view npm version
(node:13088) ExperimentalWarning: CommonJS module /home/mike/n/lib/node_modules/npm/node_modules/debug/src/node.js is loading ES Module /home/mike/n/lib/node_modules/npm/node_modules/supports-color/index.js using require().
Support for loading ES Module in require() is an experimental feature and might change at any time
(Use `node --trace-warnings ...` to show where the warning was created)
10.9.0

• Message enhancement through module: include module information in require(esm) warning nodejs/node#55397