5 TypeScript

In TypeScript 2.0, Microsoft introduced a notion called control flow based type analysis (search for it in the document if the link doesn’t work). There are similar features in Facebook’s Flow checker—hence its name—and in JetBrains’s Kotlin. You can read more about this on the Web.

How does this feature in TypeScript conflict with the type checker we have seen until now?

Your answer should not simply be that TypeScript has union types. There’s a more sophisticated answer than that.