Strip optional and undefined-type fields in typescript

strip-optional.ts

type NonNullableKeys<T extends object> = {
  [K in keyof T]: T[K] extends NonNullable<T[K]> ? K : never;
}[keyof T];
type NonOptionalKeys<T extends object> = {
  [K in keyof T]-?: {} extends Pick<T, K> ? never : K;
}[keyof T];
type OnlyDefinedFields<T extends object> = Pick<T, NonNullableKeys<T>>;

type A = {
  a: string;
  b: string | undefined;
  c?: string;
}

type B = NonNullableKeys<A>; // "a"
type C = NonOptionalKeys<A>; // "a" | "b"
type D = OnlyDefinedFields<A>; // { a: string }