typescript with ts-node and ESM support

[juergba]

Add a typescript sample using ts-node and node's native ESM support.
Note: ts-node uses Node's loader-hooks which are still experimental.

You can find info: ts-node/1007
and a working sample: ts-node/discussion

[cspotcode]

Thanks. Time permitting I'll send a pull request with a sample. Till then, I'm subscribed to this thread and can answer questions.

[Dunky13]

I'm looking for a solution on this as well

[jordaaash]

FWIW, here's a configuration for Mocha, TypeScript, and ESM that finally worked for me:
https://gist.github.com/jordansexton/2a0c3c360aa700cc9528e89620e82c3d

"node-option": ["experimental-specifier-resolution=node", "loader=ts-node/esm"] was the clincher.

[henryruhs]

@jordansexton Thank you so much, that worked for me!

package.json

{
	"type": "module"
}

tsconfig.json

{
	"compilerOptions": {
		"module": "esnext",
		"moduleResolution": "node",
	}
}

.mocharc.json

{
	"node-option": [
		"experimental-specifier-resolution=node",
		"loader=ts-node/esm"
	]
}

[fcamblor]

Thanks to all of you here, it helped me a lot :-)

I would simply add that one requirement is to use mocha@9 (mocha@9.1.3 for me) as I was on mocha@8 and I was getting following error :

TypeError [ERR_UNKNOWN_FILE_EXTENSION]: Unknown file extension ".ts"

[FauxFaux]

Hi everyone else from search results.

This only works on node 16, haven't been able to get it to work on 18 or 20.

Newer nodes don't like, and don't need(?) the "experimental-specifier-resolution=node",

[sahin52]

I'm unable to find an example like this:
chai latest version: 5.xx
mocha latest version: 10.xx
and package.json type is not module.

I can't import from chai:
import { expect, assert } from 'chai';
I'm getting:
TypeError: Unknown file extension ".ts"
for the command:
mocha -r ts-node/register -r ts-node/esm src/tests/**/*.ts if I have
"type": "module" in package.json. If I remove this, I'm getting weird typescript errors which don't exist:

Exception during run: src/tests/utils/misc.ts:166:32 - error TS2339: Property 'property11' does not exist on type '{}'.

166         (0, chai_1.expect)(obj.property11.p.b.c).to.equal(2);
                                   ~~~~~~~~~~
src/tests/utils/misc.ts:245:46 - error TS7006: Parameter 'x' implicitly has an 'any' type.

245         var compareStringsLength = function (x, y) {
                                                 ~
src/tests/utils/misc.ts:245:49 - error TS7006: Parameter 'y' implicitly has an 'any' type.

245         var compareStringsLength = function (x, y) {

[JoshuaKGoldberg]

This was done in #76. ✅

If anybody wants more TypeScript info, and there isn't an existing issue (e.g. #40) filed, please do file a new issue explaining why. Cheers! ☕