Removing ssr.format: 'cjs'

[patak-dev]

SSR CJS Format

In vite@3.0.0 we changed the default to SSR build to ESM and kept an option to use CJS as experimental for backward compatibility. Docs. Previous discussion

Starting a discussion to gather feedback on removing ssr.format: 'cjs' and legacy.buildSsrCjsExternalHeuristics in Vite 5. If you are using this feature, please share with us what is preventing the move to ESM for your SSR builds.

[cawa-93]

Does it affect build.lib.formats?

[dmitryshelomanov]

@patak-dev Please check it I did demo https://stackblitz.com/edit/github-vke2fz-67onp4?file=README.md

[patak-dev]

It works if you add this dep to noExternal: https://stackblitz.com/edit/github-vke2fz-qkvwvc?file=vite.config.ts

[dmitryshelomanov]

In dev mode ReferenceError: require is not defined
@patak-dev

[patak-dev]

Ok, please create a new bug report with this reproduction so we can properly track it there. Thanks!

[benmccann]

Issue is here: #13977. I very much doubt it's a bug in Vite. SvelteKit builds only ESM using Vite and users can use CJS libraries there

[briangleeson]

Ran into this issue recently with importing a 3rd party package, solution that worked was to use

  ssr: {
    format: "cjs",
    noExternal: ["package-name"]
  }

This may block us from upgrading to Vite v5

[benmccann]

A couple of things to try would be import * as mypkg from 'package-name' if it is a CJS package and checking that package with publint to ensure it's properly packaged

[briangleeson]

Gave it a try but got the same errors using that import approach. Running publint against the 3rd party package, it shows up a lot of warnings of the type 1. /src/example.mjs is written in ESM, but is interpreted as CJS. Consider using the .mjs extension, e.g. /src/example.mjs, and two suggestions around the package type

[itsdouges]

Anyone using Vite to bundle for Electron / VS Code extensions? The removal of this unfortunately brings a world of pain. Electron has a possible path forward at least as it supports ESM natively now, but VS Code remains blocked without native ESM yet.

Edit: Setting build.rollupOptions.output.format to "cjs" lets me move forward 😄.