Importing TypeScript file from JavaScript file with the .js extension fails.

[hornta]

Describe the bug

When I import a TypeScript file from within a JavaScript file like so export { foo } from "./my-file.js"; (my-file is a .ts file on the FS). This should not error because TypeScript files can be imported using the JS extension.

Reproduction

https://stackblitz.com/edit/vitest-dev-vitest-ivcrw5?file=test%2Fbasic.test.ts

System Info

System:
    OS: Linux 5.0 undefined
    CPU: (8) x64 Intel(R) Core(TM) i9-9880H CPU @ 2.30GHz
    Memory: 0 Bytes / 0 Bytes
    Shell: 1.0 - /bin/jsh
  Binaries:
    Node: 18.20.3 - /usr/local/bin/node
    Yarn: 1.22.19 - /usr/local/bin/yarn
    npm: 10.2.3 - /usr/local/bin/npm
    pnpm: 8.15.6 - /usr/local/bin/pnpm
  npmPackages:
    @vitest/ui: latest => 1.6.0 
    vite: latest => 5.3.2 
    vitest: latest => 1.6.0

Used Package Manager

npm

Validations

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• Read the Contributing Guidelines.
• Read the docs.
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• The provided reproduction is a minimal reproducible example of the bug.

[sheremet-va]

This is Vite's limitation. It allows using .js extension for .ts files only if the importer (index.js in your case) is also a .ts file. If you disagree with this decision, you can start a discussion or open an issue in the vite repository.

[wparsons-heins-globality]

Hey, the biggest problem with this is that it differentiates from how typescript is handling the same situation, so code that compiles just fine cannot be tested in the same way. Which for me was a big reason to drop jest for vitest in the first place.

It sounds like I'd now have to convert every single .js file to .ts to make sure we're never importing a .ts as .js, even though this is exactly what I have to do so support NodeNext module resolution.

If Vite does decide to keep it this way, is there anything we can do to get around it without migrating .js to .ts?

[nkeil]

Unfortunate to see this not supported, but seems like it's being worked on here: vitejs/vite#8993

[vjpr]

Doesn't work for .svelte files either.

https://github.com/vitejs/vite/blob/c45576ab18c42ce950ba76f0f389ad3dde2ab012/packages/vite/src/node/utils.ts#L298-L299