Typescript type utilities

type-utils.ts

// Used for flatten complex object type 
type Flatten<T> = {
  [K in keyof T]: T[K];
};

// Set K as required
type RequiredPick<T, K extends keyof T> = Flatten<
  {
    [P in K]-?: T[P];
  } & Omit<T, K>
>;

// Set K as non-nullable
type NonNullablePick<T, K extends keyof T> = Flatten<
  {
    [P in K]-?: NonNullable<T[P]>;
  } & Omit<T, K>
>;

// Set K as partial
type PartialPick<T, K extends keyof T> = Flatten<
  {
    [P in K]?: T[P] | null;
  } & Omit<T, K>
>;

// Set K as readonly
type ReadonlyPick<T, K extends keyof T> = Flatten<
  {
    readonly [P in K]: T[P];
  } & Omit<T, K>
>;