Support .cjs config files

[guillaumervls]

Description

Hello,

This is a quick* fix the use of JS config files in projects where "type": "module" is used in package.json (which will me more and more frequent now that Node 10 obsolete).
Cheers!
*The right way might be to support it via import

Performance impact

None

Security impact

None

Checklist

• My code matches the project's code style and yarn lint:fix passes.
• I've added tests for the new feature, and yarn test passes.

(not sure if that's something worth mentioning in README):

• I have detailed the new feature in the relevant documentation.
• I have added this feature to 'Pending' in the RELEASE_NOTES.md file (if one exists).
• If this is a breaking change I've explained why.

[benjie]

Could you complete this with a .mjs option? await import(...)

[guillaumervls]

I've added it, but I don't know how to do the correct switch between require and import. For now I've put a test on the file extension, but in the case of .js the correct call depends on the type field in package.json (import for module and require otherwise).

[benjie]

in the case of .js the correct call depends on the type field in package.json (import for module and require otherwise).

We could scan for this I suppose. It feels a bit expensive though since we might have to walk up a directory tree looking for a package.json which might not exist (e.g. if you're using migrate standalone). I think just requiring .mjs for now is the least painful option.

[guillaumervls]

Yes. I actually thought there could have been another solution than scanning the file system, some kind of global variable that Node sets when it's in "module" mode, that I wasn't aware of.

[benjie]

Yes. I actually thought there could have been another solution than scanning the file system, some kind of global variable that Node sets when it's in "module" mode, that I wasn't aware of.

I tried looking for this, but I've not managed to find it either. I have found an interesting behaviour though - in a commonJS file if require.main is undefined then you were started in module mode. This doesn't necessarily mean that this is what package.json states though. To see this:

// foo.mjs
import * as assert from 'assert';

assert.ok(true);
console.log("OK");
await import("./common.cjs");

// foo.cjs
const assert = require('assert');

assert.ok(true);
console.log("OK");
require("./common.cjs");

// common.cjs
console.log("Hello from common");
console.log(require.main);

Now run node foo.mjs and node foo.cjs and spot the difference.

[benjie]

Wait... Are we overthinking it?

import() can be used from both CJS and MJS files. And it can process both CJS and MJS files. So if import is available and extension is .js we can just import it and Node'll figure it out?

(As you may guess, I'm not keen to merge this until I'm certain the direction we're taking is correct.)

[guillaumervls]

Hi @benjie,

Sorry for the (very) late reply. I think you're right, I dit it here #140 (I closed this PR by accident)

Cheers !