next.js/examples/api-routes-middleware/utils/cookies.ts

import type { NextApiResponse } from "next";
import { serialize, CookieSerializeOptions } from "cookie";

/**
 * This sets `cookie` using the `res` object
 */

export const setCookie = (
  res: NextApiResponse,
  name: string,
  value: unknown,
  options: CookieSerializeOptions = {},
) => {
  const stringValue =
    typeof value === "object" ? "j:" + JSON.stringify(value) : String(value);

  if (typeof options.maxAge === "number") {
    options.expires = new Date(Date.now() + options.maxAge * 1000);
  }

  res.setHeader("Set-Cookie", serialize(name, stringValue, options));
};