demo-middleware-1.js

const restaurantOwnerOnlyMiddleware = (req, res, next) => {
    const {restaurantId} = req.params; // in this case, the id is part of the path
    const user = req.user; // available if you're using Google Firebase Authentication Middleware

    const hasPermission = (id, user) => true; // do your checks here instead

    if (!hasPermission(restaurantId, user)) {
        res.status(403).send("Unauthorized");
        return;
    }

    next(); // don't forget this. this will pass the request to the next middleware in the chain
};