Full Stack with Node.js Interview Questions in Kochi

const { z } = require('zod'); const createUser = z.object({ name: z.string().min(2), email: z.string().email(), age: z.number().int().min(18).optional() }); const validate = (schema) => (req, res, next) => { const r = schema.safeParse(req.body); if (!r.success) return res.status(400).json({ errors: r.error.issues }); req.body = r.data; next(); }; router.post('/users', validate(createUser), createUserHandler);

const session = await mongoose.startSession(); try { await session.withTransaction(async () => { await Account.updateOne( { _id: fromId, balance: { $gte: amount } }, { $inc: { balance: -amount } }, { session } ); await Account.updateOne({ _id: toId }, { $inc: { balance: amount } }, { session }); await Transfer.create([{ fromId, toId, amount }], { session }); }); } finally { await session.endSession(); } // Requires a replica set or Atlas cluster.

const server = app.listen(3000); async function shutdown(signal) { console.log(signal, 'received, closing'); server.close(async () => { await db.close(); await redis.quit(); process.exit(0); }); setTimeout(() => process.exit(1), 10000).unref(); } process.on('SIGTERM', shutdown); process.on('SIGINT', shutdown); // Stops new connections, finishes in-flight requests, closes pools.

function requestLogger(req, res, next) { const start = process.hrtime.bigint(); res.on('finish', () => { const ms = Number(process.hrtime.bigint() - start) / 1e6; console.log(`${req.method} ${req.originalUrl} ${res.statusCode} ${ms.toFixed(1)}ms`); }); next(); } app.use(requestLogger); // In production use pino-http or morgan with structured logs.

const bcrypt = require('bcrypt'); async function signup(req, res) { const hash = await bcrypt.hash(req.body.password, 12); const user = await User.create({ email: req.body.email, password: hash }); res.status(201).json({ id: user.id }); } async function login(req, res) { const user = await User.findOne({ email: req.body.email }).select('+password'); const ok = user && await bcrypt.compare(req.body.password, user.password); if (!ok) return res.status(401).json({ error: 'Invalid credentials' }); res.json({ token: signAccessToken(user) }); }

const request = require('supertest'); const app = require('../app'); // export app without calling listen describe('GET /api/v1/users/:id', () => { it('returns 404 for an unknown user', async () => { const res = await request(app) .get('/api/v1/users/000000000000000000000000') .set('Authorization', `Bearer ${testToken}`); expect(res.status).toBe(404); expect(res.body.error).toBeDefined(); }); });

const fs = require('fs/promises'); async function readConfig(path) { try { const data = await fs.readFile(path, 'utf8'); return JSON.parse(data); } catch (err) { if (err.code === 'ENOENT') return {}; throw err; } } // Or wrap any callback API with util.promisify(fn).

const path = require('path'); app.use('/api', apiRouter); app.use(express.static(path.join(__dirname, 'client/dist'), { maxAge: '1y' })); // SPA fallback for client-side routes app.get(/^\/(?!api).*/, (req, res) => { res.sendFile(path.join(__dirname, 'client/dist/index.html')); }); // Register API routes first so they are not caught by the fallback.

const asyncHandler = (fn) => (req, res, next) => Promise.resolve(fn(req, res, next)).catch(next); router.get('/:id', asyncHandler(async (req, res) => { const user = await User.findById(req.params.id); if (!user) throw new AppError('Not found', 404); res.json(user); })); // Without this, a rejected promise is never sent to the error handler. // Express 5 does this automatically.