Support named imports for JSON

[antfu]

https://stackblitz.com/edit/node-ewwreq

[privatenumber]

This problem is happening because Node.js is unable to detect whether a .ts file is commonjs/module.

I worked on a fix in esbuild-kit/esm-loader#2, which detects the package type (by detecting nearest package.json), and skips it if it's commonjs, so that it can be handled by cjs-loader.

When the fix is merged, named imports on JSON will work for CommonJS contexts.

However, it still won't work in Module contexts because native JSON modules don't support named imports by spec. We can technically override this behavior to support it but I'm not sure if we should because we don't back-port things like __filename/__dirname.

What do you think?

[antfu]

I think using named import json is quite a common convention supported by most of the bundlers. Importing a single field of a json would also enable tree-shaking for a smaller footprint. I would expect this as I might run the .ts file with the runtime in development and use bundler for production. Without this, it would be quite a hassle to deal with. I am not sure if sacrificing this to match the spec is worth it here.

[privatenumber]

Fair point. I actually encountered that exact problem when importing version from package.json, which works in Rollup/Vite.

I'm OK with overriding JSON modules to add support in esm-loader as well.

For reference on bundlers:

• Rollup's JSON plugin has named exports enabled by default. Seems this is what Vite uses too.

• Webpack 5 started to disallow named imports on JSON modules. Webpack 5 has really good CommonJS tree-shaking so they don't often incur extra costs. However, I don't think Webpack is a common bundler for Node.js targets.