We have no TS support **yet** but it's very much planned - v3 was partly about laying the foundation for it. You can track progress in [#1639](https://github.com/sveltejs/svelte/issues/1639).
You need to install a [community supported preprocessor](https://github.com/sveltejs/integrations#preprocessors) such as [svelte-preprocess](https://github.com/kaisermann/svelte-preprocess). Work is ongoing to improve [IDE support](https://github.com/sveltejs/language-tools) and build [additional CLI tooling](https://github.com/sveltejs/language-tools/issues/68)