AVA with --experimental-modules

[jim-king-2000]

Since all of my project files are *.mjs, is it possible that AVA supports native ESM? Or can I add additional node parameter "--experimental-modules" to AVA?

[novemberborn]

Whilst support remains experimental we won't support it directly, no. You can use AVA with the esm package though, see https://github.com/avajs/ava/blob/master/docs/recipes/es-modules.md.

That said perhaps we should support a way of passing options to the worker processes. We could add --node-args CLI flag, and support nodeArgs in AVA's configuration files. What do you think?

[PhilT]

Would it also require the restriction to only process *.js files to be relaxed?

[novemberborn]

@PhilT yes but that's landing soon (#1746).

I imagine AVA should use import() to load the test file too. That'll be trickier, since we currently expect a synchronous require('ava'). Still, our esm-the-package support means there's a way to hack into that process:

ava/lib/worker/subprocess.js

Line 110 in f0f0c3b

if (required[Symbol.for('esm\u200D:package')]) {

[jim-king-2000]

Hi novemberborn, thank you very much for the reply. The --node-args CLI flag or the corresponding config object is exactly what we need. I'm OK that AVA only processes *.js file. But I do need AVA support the statement like "import xxx from './yyy.mjs'" natively. Because it's a lot of extra work to introduce babel in test.

[jim-king-2000]

By the way, the esm package works well. Thank you again.

[novemberborn]

@jim-king-2000 configurable extension support has landed, so AVA can now run .mjs files. You can disable AVA's compilation of test files, or disable just the conversion of ESM to CJS.

I think the one remaining question is how AVA would actually load the files. I don't think it can use require() with --experimental-modules.

[jim-king-2000]

@novemberborn Fantastic! I tried the latest beta5 AVA and it loaded my test_*.mjs successfully. My config file is like the following. No babel any more.

"ava": {
    "require": [
      "esm"
    ],
    "babel": false,
    "extensions": [
      "mjs"
    ]
  },

[jim-king-2000]

@novemberborn I don't know how to implement it, however, I'd really like to digest "test_*.mjs" with empty config file or with a little bit more characters as the following:

"ava": {
  "node-args": [ "--experimental-modules" ]
}

[novemberborn]

I could make a ticket for the nodeArgs option, but that won't help with --experimental-modules.

We should also extend AVA's handling of esm so alternative loaders can be configured, including supporting asynchronous loaders. Then somebody could publish a package that wraps import() so it works with AVA.

Leaving this open for somebody to spec this out further.