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/issues/83) and build [additional CLI tooling](https://github.com/sveltejs/language-tools/issues/68)
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/issues/83). You can also run type checking from command line with [svelte-check](https://www.npmjs.com/package/svelte-check).