Tests to verify that sub-package bundles are valid ESM and package.json fields are correct

[keller-mark]

User story

I want to import functions from the package @vitessce/vit-s from a CDN (i.e., the dist/index.js main file).

Preferred solution

Add Cypress test that checks that the build can be imported into a plain HTML file as an ES module.

Possible alternatives

• Run the code through a CLI (node, typescript, esbuild, etc) that will throw an error if the code is not valid ESM

[ilan-gold]

@keller-mark Have you tried this? At least with Viv, the issue is not the validity of the ES code but the chain of global imports we have (which are a no-go in the browser). I think we need to create a true "bundle" if we want to do this, but I could be mistaken. deck.gl releases a minified bundle I think for this exact reason.

[keller-mark]

Ah yes that is true, we might need to use Vite/Rollup/esbuild/etc to generate a real bundle.

In addition to the global imports, the lack of .js extensions on local imports is another thing preventing direct usage of the current code in dist/

[keller-mark]

Related: https://github.com/bluwy/publint can run locally

[keller-mark]

See #1441 (comment)