Can we make typesafety look like JavaScript?

Abstract

Good news: writing complex types is usually for library maintainers… but as your project grows in size you’ll eventually find yourself authoring your own “library code”.
You now have two options: spreading type casts everywhere to please the compiler, or structuring types to get inference doing most of the work automatically.
Taking inspiration from popular open source projects, let’s analyze some patterns you can bring into your codebase to deliver clean, simple and typesafe code.