[Native ES Modules] Support for exports subpath aliasing

[aldeed]

@SimenB Great to see the list in #9430 and progress being made on it. Lots of complicated issues.

I don't see an explicit mention of handling exports object from a package when resolving package identifiers.

For example, given this in package.json:

"exports": {
    "./": "./lib/"
  },

Assuming the ESM package has a file located at /lib/foo.js, you would instead import from "package-name/foo.js" and then Node transforms that to add /lib layer.

Currently latest Jest (using Babel for parsing) does not respect this exports mapping so we have to add a matching Jest config for every dependency package that uses it:

moduleNameMapper: {
  "^package-name/(.*)$": "package-name/lib/$1"
},

Will this "just work" when native ESM support lands? If so, great, you can close this.

If not I think it should be added to your list. Thanks!

Ref: https://nodejs.org/dist/latest-v12.x/docs/api/esm.html#esm_package_exports

[SimenB]

Thanks, I'd forgotten to add it 👍 Updated the post now with this:

Node supports package exports, which sorta maps to Jest's moduleNameMapper, but also provides encapsulation features. Hopefully resolve will implement this, but if they do not we'll need to do something. Might be enough to use the pathFilter option? Unsure.

This would have been fine as a comment in that issue, btw 🙂 I'll close this as I've added the tracking item over there

[aldeed]

Thanks @SimenB !

I opened a new issue because of

Any comments added to this issue not related to how we can implement support for the below enumerated features (or to tell me I'm missing something) will be marked as spam

I see now that that sentence can be read in two different ways, and I read it the wrong way ("comments to tell me I'm missing something will be marked as spam"). Hopefully you're not missing anything else, but if I think of anything, I'll leave a comment next time. 😄

[SimenB]

Fair enough! I rephrased it now so hopefully we're down to only a single interpretation 👍

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