The guide to conditional types in TypeScript

TypeScript's introduction of conditional types since version 2.8 offers a powerful way to define type transformations based on conditions, greatly enhancing code reusability. These types function as a ternary operator at the type level, allowing developers to create recursive and distributive conditional types, which can narrow down generic types or extract specific properties. Conditional types can be refined using the infer keyword for type inference, making them versatile in scenarios like extracting property types or applying constraints. Furthermore, TypeScript's standard library includes many inbuilt conditional types, such as NonNullable, Extract, Exclude, Parameters, ReturnType, ConstructorParameters, and InstanceType, which facilitate common operations like filtering out null values or extracting function parameter types. By understanding and utilizing these advanced features, developers can write cleaner, more maintainable TypeScript code, a practice that has become integral due to the widespread use of conditional types in the language's standard library.