nullToUndefined.ts

/**
 * Converts null values in a simple JS value to undefined.
 * Useful to parse responses from graphql and erase the (arguably) useless distinction between
 * a property not having been requested vs. having been requsted and truly not existing.
 *
 * Will ignore dates, regexes, functions, maps, and sets
 * but any other object type will have it's properties recursively converted.
 */
export type NullToUndefined<T> = T extends null
  ? undefined
  : T extends Primitive | Function | Date | RegExp
    ? T
    : T extends Array<infer U>
      ? Array<NullToUndefined<U>>
      : { [K in keyof T]: NullToUndefined<T[K]> };

export function nullToUndefined<T>(value: T): NullToUndefined<T> {
  if (value === null) {
    return undefined as NullToUndefined<T>;
  }
  return (
    Array.isArray(value)
      ? value.map(nullToUndefined)
      : typeof value === 'object' &&
          !isDate(value) &&
          !isRegExp(value) &&
          !isMap(value) &&
          !isSet(value)
        ? mapValues(value, nullToUndefined)
        : value
  ) as NullToUndefined<T>;
}

export type Primitive = string | number | symbol | bigint | boolean | null | undefined;

function isDate(value) {
  return value instanceof Date && !isNaN(value.getTime());
}

function isRegExp(value) {
  return value instanceof RegExp;
}

function isMap(value) {
  return value instanceof Map;
}

function isSet(value) {
  return value instanceof Set;
}