@safejs/serializer/src/serializers/undefined/undefined.ts

Serializer is a superset of JSON that includes recursive objects, dates, regular expressions, functions and others which you also can expand by yourself

import { ConstantExtraSerializer } from "../../types";

export const undefinedSerializer: ConstantExtraSerializer<undefined> = {
    determine: (v) => v === undefined,
    deserialize: () => undefined,
};