promises.js

// all asynchronous methods have been promisified
app.post("/purchase", (req, res) => {
    user.findOneAsync(req.body)
        .then( userData => permissions.findAllAsync(userData) )
        .then( permissions => {
            if (isAllowed(permissions)) {
                return transaction.processAsync(userData);
                // userData is not defined! It's not in the proper scope!
            }
        })
        .then( confirmNum => res.send("Your purchase was successful!") )
        .catch( err => handleError(err) )
});