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Shame typescript doesn't support flow-like mode where types can sit in comments – making whole file valid js. Not everything can be expressed with jsdoc types.

You can have full TypeScript types in JSDoc-type comments: https://www.typescriptlang.org/docs/handbook/jsdoc-supported...

Not really, I want to inline /*: ... */ type annotations with terse ts code _and_ use /*:: ... */ to escape into normal typescript language where I can define arbitrary number of intermediate types and just use typescript as normal typescript, not some stripped down nonsense at limited positions.

You still can have .d.ts file and refer to that in JSDOC

Annotations on exported part only is not the whole picture of typescript.

That's also useful in mixed JS/TS project (e.g. during a migration). I wrote a short guide: https://darekkay.com/blog/javascript-type-comments/

It's better than nothing but not really a good substitute for actual Typescript.