[Vitest 3] "Intl.Collator is not a constructor" when using fake timers

[spaceemotion]

Describe the bug

I am trying to upgrade to the latest Vitest 3 Beta. Our project does not use Vite for the build-pipeline (only a simple esbuild config, in fact), and we didn't need to do anything so far to get our tests running (we don't even have a vitest config).

However, after the upgrade, we suddenly see the following error in the console:

Intl.Collator is not a constructor

TypeError: Intl.Collator is not a constructor
 ❯ src/services/xxxxx.ts:96:24
     94| };
     95|
     96| const nameComparator = new Intl.Collator('en', {
       |                        ^
     97|   sensitivity: 'base',
     98|   numeric: true,

I thought it might have to do with the Vite 6 module resolution changes, but even tinkering with that one broke more than i liked. The project runs on Node v22, and Vitest v2 has worked without an issue so far.

The error also happens when I run vitest in isolation mode.

Reproduction

https://stackblitz.com/edit/vitest-dev-vitest-ptkpew1o?file=test%2Fbasic.test.ts

Once the async import gets resolved, Vitest doesn't know what Intl. is.

System Info

System:
  OS: Linux 5.15 Ubuntu 22.04.1 LTS 22.04.1 LTS (Jammy Jellyfish)
  CPU: (16) x64 AMD Ryzen 9 7950X 16-Core Processor
  Memory: 25.82 GB / 35.24 GB
  Container: Yes
  Shell: 3.6.1 - /usr/bin/fish
Binaries:
  Node: 22.2.0 - /mnt/wslg/runtime-dir/fnm_multishells/40485_1735384937185/bin/node
  npm: 10.7.0 - /mnt/wslg/runtime-dir/fnm_multishells/40485_1735384937185/bin/npm
  pnpm: 8.15.5 - /mnt/wslg/runtime-dir/fnm_multishells/40485_1735384937185/bin/pnpm
  bun: 1.1.8 - ~/.bun/bin/bun
npmPackages:
  vitest: 3.0.0-beta.3 => 3.0.0-beta.3

Used Package Manager

pnpm

Validations

• Follow our Code of Conduct
• Read the Contributing Guidelines.
• Read the docs.
• Check that there isn't already an issue that reports the same bug to avoid creating a duplicate.
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• The provided reproduction is a minimal reproducible example of the bug.

[hi-ogawa]

This looks like due to fake timers. Here is a simplified repro https://stackblitz.com/edit/vitest-dev-vitest-96ajsug5?file=test%2Fbasic.test.ts

In v3, we changed the behavior of toFake to fake everything globally available #6288, which also includes Intl. There is a bug which breaks some Intl.xxx in @sinonjs/fake-timers and it's been fixed on upstream by sinonjs/fake-timers#479, but we are still using fairly old version 11.1.0 (latest is 14.0.0), which is before the fix.

There's a PR #7097 but probably we haven't reviewed yet.

In the mean time, you can explicitly set toFake to be same as v2 like

import { it, vi } from 'vitest';

it('repro', async () => {
  console.log('[before]', Intl.Collator);
  vi.useFakeTimers({
    // or write this in `test.fakeTimers.toFake` config
    toFake: [
      'setTimeout',
      'clearTimeout',
      'setInterval',
      'clearInterval',
      'setImmediate',
      'clearImmediate',
      'Date',
    ],
  });
  console.log('[after]', Intl.Collator);
});

[spaceemotion]

Thanks! that did the trick. I updated the title for this issue accordingly.

[hi-ogawa]

@spaceemotion feel free to try it out pre-release of the PR #7097 (comment) I confirmed the repro is fixed with this https://stackblitz.com/edit/vitest-dev-vitest-52wgjnc6?file=package.json