refactor(load-config): remove support for cjs and add support for ts

[dominikg]

Add typescript

Recently, nodejs enabled type stripping by default, and even in node 22 it can be used with the --experimental-strip-types flag. Other runtimes like deno or bun support importing local typescript files as well.

Simply rename your svelte.config.js to svelte.config.ts .

Note

Support for svelte.config.ts in sveltekit and language-tools requires a separate changes there, so for full support you still have to wait for updates there.

Remove commonjs

If you still have a svelte.config.cjs in active use, you can create a svelte.config.js like this

import config from './svelte.config.cjs'
export default config

or simply refactor it to esm. It's time.

fixes #1133
fixes #946