I have a SomeClass.ts like:

class SomeClass {
  constructor () {
    console.log('created someclass')
  }
}

export default SomeClass

Which compiles to SomeClass.js

'use strict'
exports.__esModule = true
const SomeClass = /** @class */ (function () {
  function SomeClass () {
    console.log('created someclass')
  }
  return SomeClass
}())
exports.default = SomeClass

And is imported into the script tag of App.svelte like:

<script>
  import SomeClass from "./SomeClass";

  const instance = new SomeClass();
</script>

But when running the app I get error:

Uncaught SyntaxError: import not found: default

on generated line: import SomeClass from "/src/SomeClass.js?t=1655451078055";

Note:

Just using regular ES6 flavour class & export default MyClass in SomeClass.js works fine, but might as well just remove Typescript...

Installed svelte-preprocess

npm install -D svelte-preprocess

Updated vite.config.js like so:

import { defineConfig } from 'vite'
import { svelte } from '@sveltejs/vite-plugin-svelte'
import sveltePreprocess from 'svelte-preprocess' // <--- added this

// https://vitejs.dev/config/
export default defineConfig({
  plugins: [svelte({
    preprocess: sveltePreprocess() // <--- added this
  })]
})

Deleted the compiled .js and now just work with the Typescript file directly no problems!