ts-simple-type
What is this?
Right now the type checker for Typescript API doesn't expose methods like isAssignableTo. See issue #9879 on the Typescript github repository.
To fill in the gap while this issue is being discussed this library aims to provide the most essential helper functions.
API Documentation
isAssignableToType(typeA: Type, typeB: Type, checker: TypeChecker): boolean
Tests if typeB is assignable to typeA.