Function typeMapHas

src/ytype.js:1901–1905

(parent, key)

 * @function
 */
export const typeMapHas = (parent, key) => {
  parent.doc ?? warnPrematureAccess()
  const val = parent._map.get(key)
  return val !== undefined && !val.deleted
}

/**
 * @param {YType<any>} parent