slate/node_common/middleware.js

export const init = (middleware) => {
  return (req, res) =>
    new Promise((resolve, reject) => {
      middleware(req, res, (result) => {
        if (result instanceof Error) {
          return reject(result);
        }
        return resolve(result);
      });
    });
};

export const CORS = async (req, res, next) => {
  res.header("Access-Control-Allow-Origin", "*");

  res.header(
    "Access-Control-Allow-Methods",
    "GET, POST, PATCH, PUT, DELETE, OPTIONS"
  );

  res.header(
    "Access-Control-Allow-Headers",
    "Origin, Accept, Content-Type, Authorization"
  );

  if (req.method === "OPTIONS") {
    return res.status(200).end();
  }

  next();
};