It doesn't really work fine beyond a single file.

I tried the experiment of .js files driven by typescript in JSDocs for around 10k lines and there is a night and day difference in what you can express, how and reuse it at the type level.

until you need to type the shape of objects, and want to share that shape with other files. You can't import JSDoc types from other files. At which point, you would be forced to create `types.d.ts` file or similar. Might as well be writing typescript.

The limitations are too much for complex projects at scale. I strongly believe this is why Closure types didn't take off.

That and Google's lack of developer relations around the project