Pretty sure his code is wrong!

const express = require('express');
const router = express.Router();
const { data } = require('../data/flashcardData.json');
const { cards } = data;

router.get('/:id', (req, res) => {
  const { side } = req.query;
  const { id } = req.params;
  const text = cards[id][side];
  const { hint } = cards[id];

  const templateData = { id, text };

  if (side === 'question') {
    templateData.hint = hint;
    templateData.sideToShow = 'answer';
    templateData.sideToShowDisplay = 'Answer';
  } else if (side === 'answer') {
    templateData.sideToShow = 'question';
    templateData.sideToShowDisplay = 'Question';
  }

  res.render('card', templateData);
});

module.exports = router;

extends layout.pug

block content
  section#content
    h2= text
    if hint
      p
        i Hint: #{hint}
    a(href=`${id}?side=${sideToShow}`)= sideToShowDisplay

const express = require('express');
const bodyParser = require('body-parser');
const cookieParser = require('cookie-parser');

const app = express();

app.use(bodyParser.urlencoded({ extended: false }));
app.use(cookieParser());

app.set('view engine', 'pug');

const mainRoutes = require('./routes');
const cardRoutes = require('./routes/cards');

app.use(mainRoutes);
app.use('/cards', cardRoutes);

app.use((req, res, next) => {
  const err = new Error('Not Found');
  err.status = 404;
  next(err);
});

app.use((err, req, res, next) => {
  res.locals.error = err;
  const status = err.status || 500;
  res.status(status);
  res.render('error');
});

app.listen(3000, () => {
  console.log('The application is running on localhost:3000!');
});