Extended TypeScript utility types.

extended-utility-types.d.ts

/**
 * Make all properties of T optional, except those in U. If exempt keys were already optional they'll stay optional.
 */
type Semipartial<T, U extends keyof T> = Partial<T> & Pick<T, U>;

/**
 * Make all properties of T required, except those in U. If exempt keys were already required they'll stay required.
 */
type Semirequired<T, U extends keyof T> = Required<T> & Pick<T, U>;