Typescript example: Can't use ES modules imports with Node.js AND uvu

Thanks for the tool @lukeed!

I’m having an issue with the Typescript example:

I’m trying to use ES modules directly, with the latest version of Node.js, but I can’t make test modules to work at the same time, when using imports between source modules.

I added the following (which I think it’s a pretty common use case), to the typescript example you provided:

• Added "type": "module" to package.json file, so I can use ES modules with Node.js
• Added src/main.ts file with the following content:

import { sum } from './math'

export function run() {
    console.log(sum(2, 3))
}

run()

• Added tests/main.ts file with the following content:

import { test } from 'uvu';
import * as assert from 'uvu/assert';
import * as main from '../src/main';

test('run', () => {
    assert.type(main.run, 'function');
});

• Build and test:

yarn build && yarn test

Tests work! But when I try to run emmited files with Node.js, got the following error:

node build/main.js
internal/modules/run_main.js:54
    internalBinding('errors').triggerUncaughtException(
                              ^

Error [ERR_MODULE_NOT_FOUND]: Cannot find module '/home/cristian/projects/uvu-typescript-example/build/math' imported from /home/cristian/projects/uvu-typescript-example/build/main.js

This is because ES modules imports need explicit file extension. So I fix the issue adding imports file extensions to src/main.ts (which is supported by Typescript)

import { sum } from './math.js'
...

Now building and running main file works:

yarn build && node build/main.js
yarn run v1.22.4
$ tsc
Done in 2.44s.
5

but tests don’t 😦 (got the following error):

yarn test
yarn run v1.22.4
$ uvu -r ts-node/register tests
(node:28693) UnhandledPromiseRejectionWarning: Error: Cannot find module './math.js'

Tried different tsconfig.json configurations, but can’t make the emmited files and test files to work at the same time.

[lukeed]

Oh, sorry – forgot the second half of your predicament. TypeScript can’t output mjs files (which type: "module" addresses) nor modify the output links (which is still unaddressed & causes the error you see).

I’d recommend passing everything through Rollup – here’s an example TS+Rollup setup.

But if you want to use this example as your boilerplate, you can do so by following this guide: https://github.com/microsoft/TypeScript/issues/18442#issuecomment-581738714

You’re only missing step 3: --experimental-specifier-resolution=node With that, you invoke the OG module-resolution algorithm which allows you to have extension-less imports

$ node --experimental-specifier-resolution=node build/main.js
#=> 5

[lukeed]

You’re welcome, happy to help! 😃