ESM problem `Cannot use import statement outside a module`

Prerequisites

• [ x] Checked that your issue hasn’t already been filed by cross-referencing issues with the faq label
• [ x] Checked next-gen ES issues and syntax problems by using the same environment and/or transpiler configuration without Mocha to ensure it isn’t just a feature that actually isn’t supported in the environment in question or a bug in your code.
• [ x] ‘Smoke tested’ the code to be tested by running it outside the real test suite to get a better sense of whether the problem is in the code under test, your usage of Mocha, or Mocha itself
• Ensured that there is no discrepancy between the locally and globally installed versions of Mocha. You can find them with: node node_modules/.bin/mocha --version(Local) and mocha --version(Global). We recommend that you not install Mocha globally.

Description

Steps to Reproduce

You need a test who use ES6 code from the node_modules. The esm does not work on node_modules code.

Is there any setting?!

Expected behavior: transpile all and exec tests

Actual behavior: transpilation of node_modules code does not work, since v9

Reproduces how often: [What percentage of the time does it reproduce?]

Versions

• The output of mocha --version and node node_modules/.bin/mocha --version:
• The output of node --version:
• Your operating system
• mocha: v9.0.2
  • name and version: win10
  • architecture (32 or 64-bit): win 64
• Your shell (e.g., bash, zsh, PowerShell, cmd): cmder
• Your browser and version (if running browser tests): chrome
• Any third-party Mocha-related modules (and their versions):
• Any code transpiler (e.g., TypeScript, CoffeeScript, Babel) being used (and its version):

Additional Information

[deleonio]

@juergba

Is it documented, that dependent modules must configure as type: "module".

With v8 it is not required - But with v9.

After I add type: "module" to the dependent @leanup/lib package.json - it works fine!

THX!!!

[mattgodbolt]

I’ve just hit this issue too; a third party library I used before with v8 breaks in v9 with SyntaxError: Cannot use import statement outside a module. I’m transpiling with webpack in my case (or trying to!)