Does BuckleScript do any runtime type checking? If not, you have the same problem the moment you call out into any pure JS library - your type annotations say what you expect, but JS code can merrily give you something else.
I have to admit, as much as I enjoy working with TypeScript— this same problem is always on my mind. I find myself continually writing the same tests for type safety that I would in JS. I have to remind myself that, yes the types are safe while writing, but still not quite at runtime. It can lead to pretty fundamental flaws if you’re not careful.
It wouldn't solve that, but it would prevent the code from running with data that is incorrect according to type annotations. Think of it as a runtime assert that is automatically generated from the compile-time type annotation.
(Unfortunately, the JS runtime object model does not allow for such runtime type checks to be performed with reasonable performance.)
