Fill target with default values by source via immutable, better than fp.defaultsDeep()

immutableDefaultsDeep.ts

/**
 * Fill target with default values by source via immutable
 * Benefits: unlike fp.defaultsDeep(), we don't deep clone target to get the real immutable.
 * @param target target
 * @param source source
 * @param options.ignoreArray whether append elements to array
 */
export function immutableDefaultsDeep(target: any, source: any, options?: { ignoreArray?: boolean }): any {
  const targetType = typeof target;
  const sourceType = typeof source;

  // non-empty object or array, append value recursively
  if (targetType === 'object' && targetType === sourceType && target !== null && source !== null) {
    // don't append elements to array
    if (options?.ignoreArray && Array.isArray(target)) {
      return target;
    }

    let newTarget = target;
    Object.keys(source).forEach(key => {
      const subTarget = immutableDefaultsDeep(newTarget[key], source[key], options);
      if (subTarget !== newTarget[key]) {
        if (Array.isArray(newTarget)) {
          newTarget = [...newTarget];
          newTarget[key] = subTarget;
        } else {
          newTarget = { ...newTarget, [key]: subTarget };
        }
      }
    });
    return newTarget;
  }

  // target is undefined, return source
  if (targetType === 'undefined') {
    return source;
  }

  // others: return target
  // 1.target is object && typeof target !== typeof source
  // 2.target is null
  // 3.target is number
  // 4.target is string
  // 5.target is symbol
  // 6.target is function
  // 7.target is boolean
  // 8.target is bigint
  return target;
}