Using ES Modules in API Routes / Transpilation target of api routes and modules?

[janus-reith]

I am unable to import ES Modules in API Routes.
For example when importing from https://github.com/reactioncommerce/api-utils, this fails as it won't detect the declared export in the package.json: https://github.com/reactioncommerce/api-utils/blob/5b32c0066cc93eb28155caa4507704d735694666/package.json#L26
Directly import from the /lib subfolder will then fail due to the use of imports in there, so I guess this is expected to be CJS.

Currently I could work around this by using next-transpile-modules and declaring webpack resolve aliases for that /lib subfolder in my next.config.js. (As actually, I'm dealing with multiple modules importing from each other.

Node 12 could use these without any transpilation when using the --experimental-modules and in this case, also --experimental-json-modules flags. But with serverless deployments in mind, I'm wondering if that currently is worth achieving, as somehow I did't find much information yet if Lambdas are able to deal with ESM at all.

I guess that I should aim for as as little transpilation for the server code as possible, to avoid degrading performance for some features. Like, ESM to CJS shoud be fine I guess, but I don't want a ES5 target.

However, there's tree things I wonder now:

1. Is using ES Modules a possibility?
2. What Is the default transpilation done for API routes and which target is babel using?
3. When using next-transpile-modules as part of the webpack config in next.config.js, will my modules be transpiled properly for the server target? Also, are there alternatives? I guess I would only need CJS instead of ESM, but don't require any further feature transpilation besides that happening in the API routes anyway.