Some packages use a check on module.parent to know if they are launched from CLI or required by another module:

// module.cjs
if (!module.parent) throw new Error("Running from CLI is not supported!");

This works fine if you use require (I tried from both CJS and ES modules):

$ node -p "assert.doesNotThrow(()=>require('./module.cjs')), 'No error!';"
No error!

However, when importing from ESM, that doesn't work:

// module.mjs
import './module.cjs'; // This will throw the "don't run from CLI" Error...
console.log('This is fine.'); // This is never reached

Same for dynamic imports:

// module.js // (same behaviour on ESM and CJS)
import('./module.cjs')
  .then(()=>console.log('This is fine.'))
  .catch(()=>console.log('Oh no!'))

I can see three ways to tackle this issue, but none is very satisfying to me:

• Make module.parent truthy when a CJS is imported (although I have no idea what it could look like).
• Deprecate module.parent? Packages using require.main===module are fine, so that's what library authors should be using to test this, right?
• Disregard this issue, as users can use module.createRequire to workaround the issue.