How Long It Really Takes to Judge a Full Stack Developer Candidate

"I am a full stack developer. I know HTML, CSS,
JavaScript, React, Angular, Vue, Node, Express,
Django, MongoDB, MySQL, PostgreSQL, Firebase,
AWS, Docker and Kubernetes. I have done five
projects: an e-commerce site, a chat app, a
weather app, a todo app and a portfolio."

What I hear: breadth claims I will have to test,
and no sign of which project is really theirs.

"I build web apps with React, Node and PostgreSQL.
My main project is a booking system for a small
clinic: patients pick a slot, and staff see a
daily schedule.

I built the slot API and the booking flow.
The hardest part was stopping two patients from
booking the same slot at once. I solved it with a
unique constraint on doctor and time, and showed a
clear message if the slot was taken.

I am looking for a role where I can work across
frontend and backend and grow in API design."

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

// 1. Runs for every request
app.use((req, res, next) => {
  console.log(req.method, req.path);
  next();                        // pass control on
});

// 2. Parse JSON bodies BEFORE routes read req.body
app.use(express.json());

// 3. Routes
app.post('/api/bookings', (req, res) => {
  if (!req.body.slotId) {
    return res.status(400).json({ error: 'slotId required' });
  }
  res.status(201).json({ slotId: req.body.slotId });
});

// If express.json() came after the route,
// req.body would be undefined inside it.

// A route passes errors to next(err)
app.get('/api/slots/:id', async (req, res, next) => {
  try {
    const slot = await findSlot(req.params.id);
    if (!slot) return res.status(404).json({ error: 'Not found' });
    res.json(slot);
  } catch (err) {
    next(err);                   // skip to error handler
  }
});

// Express recognises error handlers by their
// FOUR parameters. Register it after all routes.
app.use((err, req, res, next) => {
  console.error(err);
  res.status(500).json({ error: 'Something went wrong' });
});

app.listen(3000);

// A small cache where each entry expires after ttlMs
class TtlCache {
  constructor(ttlMs) {
    this.ttlMs = ttlMs;
    this.store = new Map();          // key -> { value, expiresAt }
  }

  set(key, value) {
    this.store.set(key, { value, expiresAt: Date.now() + this.ttlMs });
  }

  get(key) {
    const entry = this.store.get(key);
    if (!entry) return undefined;
    if (Date.now() >= entry.expiresAt) {
      this.store.delete(key);        // lazy cleanup on read
      return undefined;
    }
    return entry.value;
  }
}

const cache = new TtlCache(60000);
cache.set('rates', { usd: 1 });
console.log(cache.get('rates'));     // { usd: 1 }

const ratesCache = new TtlCache(60000); // 1 minute

app.get('/api/rates', async (req, res, next) => {
  try {
    const cached = ratesCache.get('rates');
    if (cached) return res.json({ source: 'cache', data: cached });

    const data = await fetchRatesFromSlowService();
    ratesCache.set('rates', data);
    res.json({ source: 'live', data });
  } catch (err) {
    next(err);
  }
});

// Follow-ups to expect:
// - Memory grows with many keys -> add a max size
// - Several servers -> each has its own cache,
//   so a shared cache like Redis may be needed
// - Many requests on expiry -> one in-flight fetch

60-SECOND PITCH

Line 1: What I build and with what
  "I build ____ with ____."

Line 2-3: Main project in plain words
  "My main project is ____ for ____."

Line 4-5: My part and one real challenge
  "I built ____. The hardest part was ____,
   which I solved by ____."

Line 6: What I want next
  "I am looking for ____."

Time it. Cut words until it fits in 60 seconds.

ANSWER EACH IN TWO SENTENCES

[ ] What is middleware in Express?
[ ] Why does middleware order matter?
[ ] What happens if next() is never called?
[ ] How do error handlers differ?
[ ] What is the difference between SQL and NoSQL?
[ ] What does a React key do in a list?
[ ] What is a REST resource?
[ ] What is an environment variable for?

Record yourself. Anything over 30 seconds
is probably too long for a warm-up.

PRACTISE ONE TASK WITH A TIMER (25 MIN)

00-03  Clarify: ask 3 questions out loud
03-06  Plan: name data structure and why
06-18  Code the simplest working version
18-22  Test: normal, empty, edge cases
22-25  Discuss one improvement

Task ideas:
- TTL cache
- Rate limiter middleware (N requests per minute)
- Group transactions by month
- Validate and save a booking form