Type flowing: Rethinking the TypeScript typing system

The concept of "type flowing" in TypeScript is explored by drawing parallels to reactive programming in RxJS, aiming to enhance understanding and usage of advanced types for everyday TypeScript work. Type flowing involves mapping and transforming subtypes from a source type to create a strongly constrained typing system, which can be achieved through tools like type aliases, conditional types, and type inference. The text illustrates how to apply this concept practically by building a well-defined type system with features such as map and filter operations, which are analogous to RxJS operators, and emphasizes the importance of type safety in preventing runtime errors. It demonstrates creating a type mapping system in a Node.js application and achieving type safety through union types. By automatically updating downstream types and alerting developers of breaking changes, type flowing ensures robust and error-free code, encouraging developers to employ TypeScript's advanced types creatively beyond just type library development.