Custom Mapped Type
This lesson explains how to create your own mapped type.
We'll cover the following...
Creating a “NonNullable” type
The first custom type shows how to use never to tell TypeScript to not compile if a custom map is not respected. The code map is a generic variable that is neither undefined nor null. In the case that the value is either one, TypeScript does not compile.
Press + to interact
type NoNullValue<T> = T extends null | undefined? never: T;function print<T>(p: NoNullValue<T>): void {console.log(p);}print("Test"); // Compile// print(null); // Does not compile
Creating a custom mapping requires ...