null-to-undefined-and-vice-versa.ts

/* eslint-disable guard-for-in, @typescript-eslint/ban-types, @typescript-eslint/no-unsafe-return, @typescript-eslint/no-unsafe-assignment */

// The nullToUndefined solution is based on these two solutions:
//
// https://stackoverflow.com/a/72549576/10580490
// https://gist.github.com/tkrotoff/a6baf96eb6b61b445a9142e5555511a0
//
// While undefinedToNull is just the reverse of it.

export type NullToUndefined<T> = T extends null | undefined
  ? undefined
  : T extends object
    ? T extends Map<infer K, infer V>
      ? Map<K, NullToUndefined<V>>
      : T extends Set<infer U>
        ? Set<NullToUndefined<U>>
        : T extends Array<infer U>
          ? Array<NullToUndefined<U>>
          : { [K in keyof T]: NullToUndefined<T[K]> }
    : T;

export default function nullToUndefined<T>(obj: T): NullToUndefined<T> {
  if (obj === null || obj === undefined) {
    return undefined as any;
  } else if (typeof obj === 'object') {
    if (obj instanceof Map) {
      const newMap = new Map();
      obj.forEach((value, key) => newMap.set(key, nullToUndefined(value)));
      return newMap as any;
    } else if (obj instanceof Set) {
      const newSet = new Set();
      obj.forEach((value) => newSet.add(nullToUndefined(value)));
      return newSet as any;
    } else {
      const newObj: Record<string, any> = Array.isArray(obj) ? [] : {};

      Object.entries(obj).forEach(([key, value]) => {
        newObj[key] = nullToUndefined(value) as any;
      })

      return newObj as any;
    }
  } else {
    return obj as any;
  }
}

export type UndefinedToNull<T> = T extends null | undefined
  ? null
  : T extends object
    ? T extends Map<infer K, infer V>
      ? Map<K, UndefinedToNull<V>>
      : T extends Set<infer U>
        ? Set<UndefinedToNull<U>>
        : T extends Array<infer U>
          ? Array<UndefinedToNull<U>>
          : { [K in keyof T]: UndefinedToNull<T[K]> }
    : T;

export default function undefinedToNull<T>(obj: T): UndefinedToNull<T> {
  if (obj === null || obj === undefined) {
    return undefined as any;
  } else if (typeof obj === 'object') {
    if (obj instanceof Map) {
      const newMap = new Map();
      obj.forEach((value, key) => newMap.set(key, undefinedToNull(value)));
      return newMap as any;
    } else if (obj instanceof Set) {
      const newSet = new Set();
      obj.forEach((value) => newSet.add(undefinedToNull(value)));
      return newSet as any;
    } else {
      const newObj: Record<string, any> = Array.isArray(obj) ? [] : {};

      Object.entries(obj).forEach(([key, value]) => {
        newObj[key] = undefinedToNull(value) as any;
      })

      return newObj as any;
    }
  } else {
    return obj as any;
  }
}