Stabilizing experimental.skipSsrTransform

[patak-dev]

skipSsrTransform

• Introduced in [email protected]
• Rationale in Original PR
• No docs
• Used by vavite

We're opening a discussion to gather feedback about this feature (in Vite 5, or probably a later version). @cyco130 it would be good if you could kick start the discussion with your current experience with this feature and thoughts regarding its stabilization.

Note: This experimental feature was moved to environments.ssr.dev.moduleRunnerTransform in Vite 7 (#20038)

[cyco130]

vavite/node-loader

I'm using this feature in the @vavite/node-loader package (PR) that implements a Node ESM loader that replaces Vite's SSR transform.

It is integrated into Rakkas and vavite CLIs but it has ~2000 weekly downloads on NPM which is more than twice as much as both combined, so people must have been using it as a standalone plugin. It works with vite-plugin-ssr, SvelteKit, SolidStart, Astro, and Qwik.js. It should also work with everything that relies on ssrLoadModule. It doesn't work with Nuxt (which uses vite-node).

Pros

• Better sourcemap support: Even though fix(ssr): load sourcemaps alongside modules #11780 is supposed to have fixed sourcemaps for SSR, I still run into occasional problems whereas the ESM loader works every time. (needs a repro of sourcemaps not working)
• Parity between dev and prod: Vite's SSR transform, although incredibly clever, has quite a few differences of behavior compared to real ESM modules. Most notably, it hides the mixed named and default exports problem in CommonJS modules, causing failures in prod that go unnoticed in dev.
• Performance: Not doing something (the SSR transform) is faster than doing it 🤷

Cons

• Node offers no way of disposing of modules which means that the ESM loader leaks memory every time a module is invalidated. The leak can only be reclaimed when the dev server is restarted.
• Node 20 runs ESM loaders in a separate VM context which breaks the current implementation that relies on global variables. It can be fixed by switching to a message passing implementation but I haven't done it yet.

Other uses

I am not aware of any other uses.

[kamarjago]

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