Call `compileModule` for `.svelte.js` files in Svelte 5

[mcous]

Howdy! I'm working on full Svelte 5 support over in @testing-library/svelte and I discovered that our suite fails with Svelte 5 + Jest + svelte-jester.

In Svelte 5, we rely on the $state rune to be able to re-render the component under test. This logic is placed in a .svelte.js file. However, if I try to send .svelte.js files through svelte-jester...

transform: {
  '^.+\\.svelte(?:\\.js)?$': ['svelte-jester'],
},

...Svelte becomes quite unhappy.

I gave vite-plugin-svelte a quick read, and discovered a new (to me) part of the transformation pipeline. It looks like there's a new compiler function - compileModule - used to compile .svelte.js files.

TL;DR: svelte-jester should probably know how to call compileModule for Svelte 5 support.

I've got a very rough proof-of-concept locally that adds enough support to get our test suite passing. Is this something you'd accept a PR for?

[mcous]

Hi @sebastianrothe, I hope you had a good weekend! Do you think you'll have time this week for these Svelte 5 PRs? I'm getting eager to ship proper Svelte 5 support in @testing-library/svelte, and I would prefer not to break Jest support while doing so

[sebastianrothe]

Hi @sebastianrothe, I hope you had a good weekend! Do you think you'll have time this week for these Svelte 5 PRs? I'm getting eager to ship proper Svelte 5 support in @testing-library/svelte, and I would prefer not to break Jest support while doing so

Yes, I am finally on it this evening.

[sebastianrothe]

I need to figure out tomorrow, how to release a next-Release for you to test.

[mcous]

Great! Let me know if I can help. For the time being, I'll try out a local build + tarball and report back

[sebastianrothe]

I think you can also use the git repo and main branch as a version number.

[mcous]

I think you can also use the git repo and main branch as a version number.

Unfortunately, due to the build step, this doesn't work. The GitHub repo has no dist directory, where the main export is output by rollup

I'll try out a local build + tarball and report back

Everything is checking out locally on my end! In Svelte 5, I am now able to specify...

{
  transform: {
    '^.+\\.svelte(?:\\.js)?$': 'svelte-jester',
  },
}

...in Svelte 5 and the v5 syntax (runes) works outside Svelte components as expected

[sebastianrothe]

Great, I will create a release with version number 5.

[sebastianrothe]

Published as 5.0.0 https://www.npmjs.com/package/svelte-jester 🚀