Cypress shows multiple warnings "ExperimentalWarning: Custom ESM Loaders ..." for Node.js `>=20.0.0 <=20.6.0`

[MikeMcC399]

Current behavior

After installing and opening Cypress with Node.js >=20.0.0 <=20.6.0, multiple error messages are output, similar to:

<<<CYPRESS.STDERR.START>>>(node:4910) ExperimentalWarning: Custom ESM Loaders is an experimental feature and might change at any time

Desired behavior

Cypress should not throw multiple error messages on versions of Node.js it allows in the engines field of package.json:

cypress/cli/package.json

Lines 122 to 124 in d0570f8

	"engines": {
	"node": "^20.0.0 || ^22.0.0 || >=24.0.0"
	},

Attempting to improve the experience of running under low minor versions of Node.js 20 would not be a productive investment, since Node.js effectively only supports the latest release in each Node.js release line. The minimum Node.js 20.x version should be raised to rule out using problematic versions Node.js >=20.0.0 <=20.6.0

I suggest using Node.js 20.9.0, released on Oct 24, 2023. This was the release marking the transition of Node.js 20.x into Long Term Support (LTS) and it could be a suitable milestone with which to align for support purposes.

Test code to reproduce

cd $(mktemp -d)
npm install cypress
npx cypress open

Cypress Version

15.0.0
This is a regression from 14.5.4, where the issue does not occur.

Node version

v20.0.0 - v20.5.1

Operating System

Ubuntu 24.04.3 LTS

Debug Logs

$ npx cypress open

DevTools listening on ws://127.0.0.1:43683/devtools/browser/81330447-ef9b-45ef-bc3b-176aeff3c5b5
[4513:0901/201450.546843:ERROR:ui/gfx/x/atom_cache.cc:232] Add _NET_WM_WINDOW_TYPE_INDEX to kAtomsToCache
<<<CYPRESS.STDERR.START>>>(node:4910) ExperimentalWarning: Custom ESM Loaders is an experimental feature and might change at any time
(Use `node --trace-warnings ...` to show where the warning was created)
<<<CYPRESS.STDERR.END>>><<<CYPRESS.STDERR.START>>>(node:4910) ExperimentalWarning: Custom ESM Loaders is an experimental feature and might change at any time
(Use `node --trace-warnings ...` to show where the warning was created)
<<<CYPRESS.STDERR.END>>><<<CYPRESS.STDERR.START>>>(node:4910) ExperimentalWarning: Custom ESM Loaders is an experimental feature and might change at any time
(Use `node --trace-warnings ...` to show where the warning was created)
<<<CYPRESS.STDERR.END>>>

Other

Node.js 20 release line milestone releases:

• Node.js 20.0.0 release Apr 18,2023
• Node.js 20.6.0 release Sep 4, 2023
• Node.js 20.9.0 release Oct 24, 2023, first LTS release
• Node.js 20.19.4 release Jul 15, 2025, latest maintenance LTS release

[jennifer-shehane]

@MikeMcC399 Is this new in Cypress 15?

[MikeMcC399]

@jennifer-shehane

Is this new in Cypress 15?

Yes, it's a regression in Cypress 15.0.0 compared to Cypress 14.5.4 (edit: added this information to the original post). Executing the same steps, except specifying cypress@14 under Node.js v20.0.0 in Ubuntu 24.04.3 shows only the following in the logs. There are no ExperimentalWarning entries.

DevTools listening on ws://127.0.0.1:44021/devtools/browser/253fb35a-e74e-4cc7-9d35-31285bb26f97
[4851:0902/173924.347697:ERROR:atom_cache.cc(229)] Add _NET_WM_WINDOW_TYPE_INDEX to kAtomsToCache

cd $(mktemp -d)
npm install cypress@14
npx cypress open

[laurentS]

I can confirm seeing the same behaviour (ie. a regression) on an actual codebase.

[MikeMcC399]

@laurentS

I can confirm seeing the same behaviour (ie. a regression) on an actual codebase.

As far as usage is concerned, it would be recommended to use the latest Node.js 20 LTS version (currently 20.19.4), since Node.js officially only supports the latest release in each release line.

It may be that the resolution to this issue could be a documentation change only.

I also saw in my tests that they succeeded even though there were warnings.

[laurentS]

As far as usage is concerned, it would be recommended to use the latest Node.js 20 LTS version (currently 20.19.4), since Node.js officially only supports the latest release in each release line.

Indeed, this is what I'm doing now. I use nvm to switch versions, and had incorrectly assumed that nvm use v20 would automatically put me on the latest minor version. This is how I found this bug.

[MikeMcC399]

@laurentS

Indeed, this is what I'm doing now. I use nvm to switch versions, and had incorrectly assumed that nvm use v20 would automatically put me on the latest minor version. This is how I found this bug.

It's a little off-topic here, but if you are using macOS or Linux n is a good alternative to nvm and you don't need two steps to select a version like nvm install / nvm use

[MikeMcC399]

@jennifer-shehane

My suggestion would be to add a section underneath https://docs.cypress.io/app/references/troubleshooting#Update-Cypress to recommend checking with the https://docs.cypress.io/app/get-started/install-cypress#System-requirements. For Node.js recommend using the latest possible version from the listed supported Node.js versions.

• Make no changes to Cypress regarding this issue
• Make no other documentation changes

and then close this issue.

[MikeMcC399]

• PR chore: update tsx to 4.20.5 #32469 bumped engines min Node.js to ^20.1.0

cypress/cli/package.json

Lines 122 to 124 in 484b177

	"engines": {
	"node": "^20.1.0 || ^22.0.0 || >=24.0.0"
	},

If this has set a precedent for a breaking change without declaring it as such, then the minimum could be bumped further up to ^20.6.0, also as a chore type commit.