MarkReadonly<Type, Keys> constructs a type by picking all properties from type Type where properties Keys are set
to readonly, meaning they cannot be reassigned
interface User {
id: number;
name: string;
email: string;
}
type UserThatCannotChangeEmail = MarkReadonly<User, "email">;
// ^? { id: number; name: string; readonly email: string }Useful when in current context a set of properties cannot be reassigned
declare const user: UserThatCannotChangeEmail;
// error: Cannot assign to 'email' because it is a read-only property
user.email = "[email protected]";
// ^^^^^TS Playground – https://tsplay.dev/NaEZ0N