toSerializable.ts

type AnyValue =
  | { [key: string]: AnyValue }
  | { [key: number]: AnyValue }
  | AnyValue[]
  | string
  | number
  | boolean
  | null
  | undefined
  | symbol
  | BigInt
  | ((...args: AnyValue[]) => AnyValue);

type SerializableValue =
  | { [key: string]: SerializableValue }
  | { [key: number]: SerializableValue }
  | SerializableValue[]
  | string
  | number
  | boolean
  | null
  | undefined;

export default function toSerializable<
  TInput extends { [key: string]: AnyValue } | { [key: number]: AnyValue } | AnyValue[] | AnyValue,
>(input: TInput): SerializableValue {
  if (input == null) return input;

  return Array.isArray(input)
    ? input
        .filter(shouldKeep)
        .map((item) => (typeof item === 'object' ? toSerializable(item) : item))
    : Object.fromEntries(
        Object.entries(input)
          .filter(([, v]) => shouldKeep(v))
          .map(([key, value]) => [key, typeof value === 'object' ? toSerializable(value) : value]),
      );
}

// eslint-disable-next-line @typescript-eslint/ban-types
type MakeSerializable<TInput> = TInput extends BigInt | symbol | Function ? never : TInput;

function shouldKeep<TItem>(item: TItem): item is MakeSerializable<TItem> {
  return !['function', 'symbol', 'bigint'].includes(typeof item);
}