[Flow] static type checker is a wonderful attempt to bring [algebric data types] to JS. It is still fairly new project and there for has few WTFs that can pull you down the rabbit hole. This document is attempt to document things that may seem like a WTF from the perspective of JS developer who tries to employ static type checker, or in other words, some items on the list may be very subjective & based on the background of the writer.
Polymorphic type that is a function
It is very likely that one will wind up using [Polymorphic functions] to solve a more general problem. And if you define type alias for such a function you may be puzzled what is the right syntax should be used for such type definition.
Let's start with: