[zarzavat]

That is true for nominal type systems such as Java’s.

However TypeScript’s structural typing is much more flexible, because it is designed to describe the types of all the existing JavaScript code out there (via the DefinitelyTyped project).

This gives the best of both worlds: the freedom to express the architecture you need, plus the freedom to actually refactor an existing code base into that new architecture without introducing many bugs. Dynamically typed languages give you the former but not the latter.