Welche Felder haben StringFields und NumberFields?

type PickByType<T, U> = {
  [K in keyof T as T[K] extends U ? K : never]: T[K];
};

interface Model {
  id: number;
  name: string;
  active: boolean;
  email: string;
  age: number;
}

type StringFields = PickByType<Model, string>;
type NumberFields = PickByType<Model, number>;