express_payment_demo.js

const express = require('express');
const app = express();
const port = 4000;

// Payments

// In the real world, we would use a real database like Postgres or MongoDB. Just in memory for the sake of this example.
const payments = {};
/** POST /payment - Create a payment.
 * @typedef Payment
 * @property {number} amount - The amount of the payment.
 * @property {string} fullName - The full name on the card.
 * @property {string} exp - The expiration date.
 * @property {string} ccv - The ccv.
 * @property {string} cardNumber - The last 4 digits of the card number.
 * 
 */
app.post('/payment', async (req, res) => {
  const { amount, fullName, cardNumber, exp, ccv } = req.body;
  const id = uuidv4();
  payments[id] = { amount, fullName, exp, ccv, ccLast4: filterCreditCardNumber(cardNumber),
    // Only store this token until we run the charge, then delete.
    token: getPaymentToken() 
  };

  // Asynchronous token retrieval; more performant, but more complex to keep our data consistent.
  // getPaymentToken.then(token => {
  //   payments[id].token = token;
  // });
  
  // Syncronous token retrieval; less performant, but simpler to keep our data consistent.
  await getPaymentToken(amount, fullName, cardNumber, exp, ccv)
    .then(token => {
      payments[id].token = token;
      res.status(201).json({id});
    })
    .catch(err => {
      // Ping oncall
      // i.e. Bugsnag.notify(err) or Sentry
      res.status(500).json({error: 'Failed to get payment token'});
    });
});

/** GET /payment - Get all payments.
 * 
 */
app.get('/payment', (req, res) => {
  const paymentsArray = Object.entries(payments).map(({token, ...props}) => ({ ...props }));
  res.json({payments: paymentsArray});
});

function filterCreditCardNumber() {
  const last4Digits = cardNumber.slice(-4);
  return last4Digits;
}

/**
 * Get a payment token from the payment processor. Token then can be used to charge card later.
 * 
 * @param {number} amount - The amount to charge.
 * @param {string} fullName - The full name on the card.
 * @param {string} cardNumber - The card number.
 * @param {string} exp - The expiration date.
 * @param {string} ccv - The ccv.
 * @returns {Promise<string>} - The payment token.
 */
async function getPaymentToken(amount, fullName, cardNumber, exp, ccv) {
  // Fake; in real life, we would call the payment processor's API like Stripe.
  return uuidv4();
};

// Start the app.
app.listen(port, () => {});