Unable to import 'postprocessing' in ESM-based Node.js

[donmccurdy]

I'm using Ava and Node.js to run unit tests, and postprocessing is in the dependencies of the tested code. When running the tests, Node.js hits this error:

SyntaxError: The requested module 'postprocessing' does not provide an export named 'Effect'

Of course postprocessing does export Effect, in fact. I think this comes down to nodejs/node#32137. Node.js expects that ES Modules will either (a) use "type": "module" or (b) use .mjs, if I understand this correctly. Because postprocessing currently does neither, it cannot resolve the import.

This isn't urgent for me, but I just wanted to flag the issue. I see Remove CJS bundles, change type to module on the roadmap; that would certainly solve the issue as far as I'm concerned. I believe it would be a non-breaking change to add "type": "module" now, as long as you keep the main entry and change its extension to .cjs. Example:

https://github.com/donmccurdy/KTX-Parse/blob/d7e7fefbef44642d5dbb9444a64bc055d4483ce8/package.json#L5-L14

EDIT: I'm testing with Node v18.5.0

[vanruesc]

This would be a breaking change because it causes issues for React and Webpack 4 builds (#277, #312, #346, pmndrs/react-postprocessing#114).

You could import from postprocessing/module instead which exports an .mjs bundle for Ava.js testing, but that export will also be removed in v7.

[donmccurdy]

Sorry, I don't think I follow the connection with those threads — the example config from ktx-parse is what I'm proposing, and hoping might not be a breaking change. I'm not proposing that postprocessing use .mjs files. I don't mind waiting for v7 either, though. Thanks!

[vanruesc]

Those threads were problems that occured after I tried changing the package type to module or the extension of the bundle to .mjs. I don't remember the exact configs I tried, but it all turned out to be a breaking change in some way or another. Maybe the configuration you propose is actually non-breaking, but I'd rather make the change in v7.

[donmccurdy]

Makes sense, thanks! The whole cjs / mjs situation is really something. I'm glad to see more packages moving to ESM-first. Let me know if I can help here, or feel free to close the issue if this is already covered by the roadmap.