Sort of, via preprocessing, but you won't get any real benefit from it at present. There are two barriers: the compiler itself needs to become TS-aware, and we need to teach editors like VSCode how to typecheck inside <script> blocks.

It's very much on the radar (I'm a TS convert, personally — Svelte itself is written in TypeScript), we just need to get round to it. The version 3 rewrite was largely about laying the foundations for TS support.

Svelte itself has been on my radar for quite a while - I think when proper TypeScript support lands, that will be the first time I'll actually give it a try for one project or another. The idea is intriguing, thanks for working on it!

Do you have any estimate on how much work that'll be? Do you think you'll be able to land TS support (including type-checking through the command line) within half a year, or is that a bigger thing?