TypeScript and ESM

TypeScript example doesn’t work for my project with:

1. Sources in JS ESM (to avoid compiler)
2. Tests in TypeScript ESM
3. "type": "module" in package.json

Repository to reproduce the error.

$ git clone [e-mail]:ai/nanodelay.git
$ git checkout uvu
$ yarn
$ yarn test
uvu -r ts-node/register test && eslint . && check-dts && size-limit && yaspeller *.md
Error [ERR_REQUIRE_ESM]: Must use import to load ES Module: /home/ai/Dev/nanodelay/test/index.test.ts
require() of ES modules is not supported.
require() of /home/ai/Dev/nanodelay/test/index.test.ts from /home/ai/Dev/nanodelay/node_modules/ts-node/dist/index.js is an ES module file as it is a .ts file whose nearest parent package.json contains "type": "module" which defines all .ts files in that package scope as ES modules.
Instead change the requiring code to use import(), or remove "type": "module" from /home/ai/Dev/nanodelay/package.json.

    at createErrRequireEsm (/home/ai/Dev/nanodelay/node_modules/ts-node/dist-raw/node-cjs-loader-utils.js:86:15)
    at assertScriptCanLoadAsCJSImpl (/home/ai/Dev/nanodelay/node_modules/ts-node/dist-raw/node-cjs-loader-utils.js:19:11)
    at Object.require.extensions.<computed> [as .ts] (/home/ai/Dev/nanodelay/node_modules/ts-node/src/index.ts:1288:5)
    at Module.load (node:internal/modules/cjs/loader:975:32)
    at Function.Module._load (node:internal/modules/cjs/loader:816:12)
    at Module.require (node:internal/modules/cjs/loader:999:19)
    at require (node:internal/modules/cjs/helpers:93:18)
    at /home/ai/Dev/nanodelay/node_modules/uvu/run/index.js:9:3
    at Array.forEach (<anonymous>)
    at Object.exports.run (/home/ai/Dev/nanodelay/node_modules/uvu/run/index.js:6:9)

Removing "type": "module" from package.json solves the problem, but break my no compiler workflow.

[lukeed]

I just finished putting together loadr, which is the thingy in my snippet above 😆

With it, @alextes’ example can be change from:

$ node --experimental-loader ts-node/esm node_modules/uvu/bin.js src '.*.test.ts'

to

$ loadr -- npm test
# assumes "test": "uvu src '.*.test.ts'"

It just needs a loadr.mjs configuration file:

export const loaders = ['ts-node/esm'];

Of course, your test command could also include the loadr command directly:

// package.json
{
  "scripts": {
    "test": "loadr -- uvu src '.*.test.ts'"
  }
}

This doesn’t change anything about the original ESM + TS issue, but it’s just a tool to cleanup the absurd amount of CLI paths and/or --experimental-loader flags you’re throwing around 😆

[talentlessguy]

another way would be using esbuild-node-loader:

node --experimental-loader esbuild-node-loader node_modules/uvu/bin.js tests

I currently use that in most of my libraries