types.ts

/**
 * Exposes type utility functions.
 * @packageDocumentation
 */

/**
 * Does `x` have an undefined property `prop`,
 * or that property is `PropType`?
 */
export function haveUndefienedPropertyOrThat<
  PropType,
  Base,
  Prop extends keyof Base
>(p: (a: unknown) => a is PropType, x: Base, prop: Prop): boolean {
  const xa = (x as {[P in Prop]?: unknown})[prop]

  return xa === undefined || p(xa)
}