Multiple ESM Edition Autoloader

[balupton]

Here is an attempt at a multiple ESM edition autoloader to test if the foundations are possible. It seems they are not, as it returns a promise, as dynamic imports return promises, so the exports will be promises, which is inconsistent API with the CJS Autoloader.

import { readFileSync } from 'fs'
function readJSON(path) {
	const text = readFileSync(path, 'utf8')
	return JSON.parse(text)
}

import path from 'path'
import url from 'url'
const root = path.dirname(url.fileURLToPath(import.meta.url))
const pkgPath = path.join(root, 'package.json')

function load() {
	const data = readJSON(pkgPath)
	for (const edition of data.editions) {
		if (
			edition.tags &&
			edition.tags.includes('import') &&
			edition.engines &&
			edition.engines.node
		) {
			const editionPath = path.join(root, edition.directory, edition.entry)
			return import(editionPath)
		}
	}
}

const d = load()
// can't export
export default d.default || d

As such, only a single ESM edition for Node seems to be able to be supported by packages.

[balupton]

For editions v4, it can be accomplished via a index.mjs file like so:

'use strict'
// auto-generated by boundation, do not update manually
/** @type {typeof import("./compiled-types/index.d.ts") } */
import { requirePackage } from 'editions'
import filedirname from 'filedirname'
const [__filename, __dirname] = filedirname(import.meta.url)
const pkg = await requirePackage(__dirname, (path) => import(path))
export default pkg.default || pkg

However, this still suffers from the promise return, and causes incompatibilities with anything but the default export:

// doesn't work via the autoloader
// import { nullish } from './index.mjs'
// nullish(null, 'nullish worked')

// autoloader requires
import pkg from './index.mjs'
pkg.nullish(null, 'nullish worked')

// direct consumption requires
import { nullish } from './edition-esnext-esm/index.js'
nullish(null, 'nullish worked')

As such, there will need to be a way to write static exports for everything, or boundation must only generate one esm edition, and not use an esm autoloader.