Use ES Modules with type:module

[fregante]

It'd be great to have just be a Node-compatible ES Module with type: "module" in the package.json

I don't remember if there's a backwards-compatible way to have both CJS and type:module in the same import, but this is definitely possible:

- index.js // cjs file
- esm/index.js // esm file
- esm/package.json // Content: `{"type": "module"}`

This would enable both:

const something = require('just-something');

import something from 'just-something/esm'; // Notice the `/esm`

[angus-c]

yes I should look into this, thanks

[boogerlad]

any update on this?

[angus-c]

Sorry I haven't had the time to get to this. In theory it should be fairly simple (if repetitive) but I wanted to take the time to verify a POC before making updates. Will try to look at this over the holidays.

[antony]

one option which can save time with this is to add a small 3-4 line rollup file which compiles an es6 version of the library into dist which can just be done at packaging time.

There's an example of this here: mcollina/fastq#48

[raulfdm]

@angus-c want some help on this task?

[angus-c]

@angus-c want some help on this task?

sure!

[PCOffline]

Hey, any updates with this?

[raulfdm]

@angus-c I was about start but I think, before any work, we should discuss how we want to do that.

I believe there are some strategies to make it work.

Copy strategy

If we don't want to change anything, we could simply:

1. make a index.js copy and name index.esm.js
2. replace the module.exports with export default
3. Add the property type: module to inform that ESM should take precedence if supported;
4. Point the index.esm.js file as module ("module": "index.esm.js)

The problem with that is we'll end up having duplicated code. If something needs to be fixed, it'll need to be done in 2 places.

Single source of truth

Since every package is self contained and written in CJS way, we could use a transpiler tool like SWC, ESbuild, or Rollup and then:

1. write a script to transform index.js into index.esm.js targeting esm;
2. Add in the package.json the module and type;
3. include that new file to published

Since you're using a monorepo, it won't be much work. The only thing we should be aware is to run the build process for every new publish.

---

I only can see these 2 approaches, let me know what you want to do so I can help in a more assertive way.

Cheers.

[PuruVJ]

I second this and would love to help with transition. I'm already building a library on top of just, and this move will resolve tree-shaking issues in that

[angus-c]

@raulfdm Yeah I prefer the second option, for maintainability. Running the new build process on publish should be no problem

[raulfdm]

@angus-c I've just opened a PR with a proposal.

I did for one single package to align with you the direction. If you agreed I'll do for all packages. Otherwise we can refine the approach until we get in strategy I can following for all other packages.