Documentation Request: Using a Node Custom Loader

[F1LT3R]

I really love ava, and I'm trying to build a case for using across all of our web projects at work.

But I'm running into an issue trying to use ava to test Web Components using relative imports as JavaScript Modules in the browser.

When I use ava I get the typical Node ESM Error:

[ERR_UNSUPPORTED_DIR_IMPORT]:
    Directory import '/home/user/my-project' is not supported resolving ES modules imported from ...
    /home/user/repos/my-other-project

I spent yesterday afternoon looking through your old bug reports, and your documentation on using ESM Loaders of various flavors, and I think the best way to go is using my own Node Custom Loader. Especially as there are special rules, such as: using Babel style imports, where extensions may be excluded for: .html, .js, .mjs; and conditionally serves index.html or index.mjs when hitting a directory /. (These are being handled by a custom http server).

What I can't find documented is how I would use my own custom loader with ava, assuming it's just a loader script running in my project.

Example of running my custom loader:

 node --loader ./loader.mjs web/components/my-component.mjs

Example of relative import from my-component.mjs:

import MyOtherModule from '../my-other-module'   // <-- loads '../my-other-module/index.mjs'

Perhaps there is a simple way to do this already, which I have missed?

I'm really just looking to use ava in a way that will respect a project level entry point to a loader.mjs that lives as a script within that same project, rather than using a node module name and package to handle loading.

If you guys are willing to help me get ava to work with a project based entry point to loader.mjs, I would be more than happy to be involved in any PRs, if any were necessary, and update your documentation myself.

[novemberborn]

This is an experimental Node.js feature. There are enough hooks within AVA (nodeArguments) and through environment variables NODE_OPTIONS to configure custom loaders. However the behavior keeps changing in Node.js so it tends to break a lot. There's plenty of discussion in this forum about all the different things to try.

[F1LT3R]

Thanks @novemberborn, I didn't realize loaders were still experimental. Thanks for the tip, I'll look around the forum see how far I can get.

[F1LT3R]

I spent some time looking through the forums and did some spelunking through the codebase, and I was not able to get AVA to use my custom ESM loader - even though Node said it was loaded. I have a feeling that AVA is not exporting the methods that Node 21's loader is using.

Node.js built in testing framework did work with my custom loader though, so for now that's probably the better option.

Looking forward to when AVA supports non-experimental loaders.

[novemberborn]

AVA does nothing special. It will either require() or import() your test file. The whole point of loaders is that regular code does not need to be changed.

More likely the loader configuration isn't making it to the worker thread. It is experimental after all.

[make-github-pseudonymous-again]

Recently, my --experimental-loader configuration using @node-loader/core was broken. Today, Node warns you about using --experimental-loader and gives away the solution:

     "nodeArguments": [
-      "--experimental-loader=@node-loader/core"
+      "--import=data:text/javascript,import {register} from 'node:module'; import {pathToFileURL} from 'node:url'; register('@node-loader/core', pathToFileURL('./'))"
     ],