Vite Struggles with Exports

[shellscape]

Any chance of getting an ESM version or some default export shimming introduced? vite dev dislikes the package immensely, throwing an error which resembles:

Uncaught SyntaxError: The requested module '/@fs/private/tmp/jsx-email-starter/node_modules/.pnpm/extend@3.0.2/node_modules/extend/index.js?v=ae42d2d7' does not provide an export named 'default' (at index.js?v=ae42d2d7:350:8)

unified is making use of this package (and is ironically ESM-only) and running vite with anything that wants to use unified is quite impossible without extensive gymnastics.

[justmoon]

This has come up before, see #57.

After playing around with adding ESM support, the issue is that this module currently supports very old Node.js versions which obviously don't support ESM at all. Adding a transpiler or maintaining two copies of the code and tests adds a lot of complexity.

To add ESM support for this module, the best way imo would be to make a new major version which fully switches to ESM and drops support for Node.js versions <12. Kind of like what @sindresorhus has done with his packages. Users of older Node.js versions could continue to use the older version of the package.

I'd be fine with that but @ljharb has been the primary maintainer for this package, so he'd have to agree.

[ljharb]

Have you filed an issue on vite? It should be able to handle all existing CJS packages, or else it's broken.

As for ESM-only packages, if you look at adoption numbers for basically all of them, without exception, the vast majority remains permanently stuck on the last CJS version - iow, it's objectively proven to be a failed initiative.

We could certainly ship a .mjs file and the exports field - VERY carefully, so as to not make it a breaking change - that would re-export all the properties on the CJS module.exports as named ESM exports, but that simply shouldn't be necessary. node itself uses cjs-module-lexer to figure out things like this for its native ESM implementation, so vite certainly should be able to.

[milesaylward]

Old issue but if anyone is using Vite and stumbles on this as I did the simplest solve I could find was to include extend in vite's optimizeDeps config.

optimizeDeps: {
  include: ['extend']
}