Full Stack with Node.js Interview Questions in Visakhapatnam
36 practice questions with answers for Full Stack with Node.js interviews in Visakhapatnam.
Full Stack with Node.js jobs in Visakhapatnam
Visakhapatnam (Vizag) has a developing IT market with delivery centres, start-ups and IT parks around Rushikonda. Many local candidates also apply to Hyderabad and remote roles, so a mix of service and product styles is common.
Below are 36 questions that match the mix of service, product and domain employers hiring node.js developers in Visakhapatnam.
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01
How would you test code that depends on the current time, like an expiring coupon?
Inject a clock function instead of calling Date.now directly, or use Jest fake timers: jest.useFakeTimers().setSystemTime(new Date('2026-01-01')). Then test before, exactly at and after expiry. Store dates in UTC and convert for display in IST, which avoids bugs near midnight. Reset timers after each test with jest.useRealTimers to avoid leaking into other tests.
helmet is middleware that sets secure HTTP response headers. It adds Content-Security-Policy, Strict-Transport-Security, X-Content-Type-Options nosniff, frame protection and removes X-Powered-By, reducing risks like clickjacking, MIME sniffing and some XSS attacks. It is one line, app.use(helmet()), but CSP usually needs tuning so your frontend scripts and assets still load.
Use WebSockets through Socket.IO or ws, or Server-Sent Events for one-way updates. Clients join a room per order, and when the rider location or status changes, the server emits to that room. With multiple instances, use the Socket.IO Redis adapter so events reach clients on any server, authenticate the socket on connect, and throttle location updates to save bandwidth.
06
A dashboard endpoint makes five independent database queries one after another and takes 1.5 seconds. How would you speed it up?
Because the queries are independent, run them concurrently with Promise.all so total time is close to the slowest query instead of the sum. Check that the database connection pool is large enough to serve them in parallel. Then add indexes for slow queries, cache rarely changing parts in Redis, and use Promise.allSettled if the page can render with some widgets missing.
07
You must change a response field name used by many clients. How do you do it without breaking them?
Treat it as a breaking change. Option one: add the new field alongside the old one, mark the old field deprecated in docs and response headers, track usage through logs and remove it after clients migrate. Option two: release it in /v2 and keep /v1 for a deprecation window. Communicate timelines clearly and add contract tests for both.
08
Compare Prisma, Sequelize and TypeORM for SQL databases in Node.js.
Prisma uses a schema file to generate a fully typed client and has excellent TypeScript support and migrations, though complex raw SQL needs escape hatches. Sequelize is mature, promise-based and widely used in older JavaScript projects. TypeORM uses decorators and entity classes, familiar to Java and NestJS developers. Drizzle is a newer lightweight, SQL-like typed option. Pick based on TypeScript use and team familiarity.
09
What is the purpose of the util.promisify function?
util.promisify converts a function that follows the Node callback convention, where the last argument is (err, result) => {}, into one that returns a promise. This lets you use async and await with older APIs. For example, const sleep = util.promisify(setTimeout) or promisify(fs.readFile). Many core modules now offer promise versions directly, such as fs/promises and dns/promises.
10
Should you use serverless functions like AWS Lambda for a Node.js API?
Serverless suits spiky or low-traffic workloads, event processing and quick prototypes, since you pay per invocation and need no server management. Downsides are cold starts, execution time limits, connection handling with relational databases and harder local debugging. For steady high traffic or long-lived WebSocket connections, containers are usually cheaper and simpler. Many teams mix both.
11
What is contract testing and why is it useful for microservices?
Contract testing verifies that a provider API and its consumers agree on request and response formats without running the whole system. With Pact, the consumer writes expectations that become a contract, and the provider runs them in its own CI. It catches breaking changes like a renamed field before deployment, and is faster and less flaky than full end-to-end environments.
12
What is SQL injection and how do you prevent it in Node.js?
SQL injection happens when user input is concatenated into a query, letting attackers change it, for example ' OR 1=1 --. Prevent it with parameterised queries, such as pool.query('SELECT * FROM users WHERE email = $1', [email]) in pg, or an ORM like Prisma or Sequelize that parameterises automatically. Also validate input and give the database user minimum privileges.
13
Your Node.js API becomes unresponsive when one endpoint generates a large PDF report. What is happening and how do you fix it?
The PDF generation is CPU-bound and blocks the single event loop, so every other request waits. Fixes: move the work to a worker_threads pool such as Piscina, or push it to a background job queue like BullMQ with Redis and return a job ID that the client polls. Also break large loops into chunks and measure event loop lag to confirm the fix.
14
How does error-handling middleware work in Express?
Error-handling middleware has four parameters (err, req, res, next) and must be registered after all routes. When any middleware calls next(err) or throws in a synchronous handler, Express skips normal middleware and jumps to the error handler. In Express 4, async errors must be passed to next manually or with a wrapper; Express 5 forwards rejected promises automatically.
15
Why do you want to work as a Node.js backend developer?
I enjoy building the systems behind products: APIs, data models and integrations. Node.js lets me use JavaScript across the stack and ship features quickly, and I like solving problems around performance and reliability. In my projects I built a REST API with authentication, MongoDB and Docker deployment, and I want to grow by working on real traffic and learning system design from experienced engineers.
Soft delete marks a record as deleted with a flag or deletedAt timestamp instead of removing it, so data can be restored and audited. Trade-offs: every query must filter out deleted rows, unique constraints need care, tables grow over time and privacy laws such as India's DPDP Act may require real deletion of personal data on request. Use partial indexes and periodic purging.
17
Implement cursor-based pagination for a products endpoint.
localStorage is readable by any JavaScript on the page, so an XSS bug can steal tokens. HttpOnly, Secure, SameSite cookies cannot be read by JavaScript, which is safer for refresh tokens and session IDs. Cookies require CSRF protection, which SameSite=Lax or Strict plus CSRF tokens provide. A common pattern keeps the access token in memory and the refresh token in an HttpOnly cookie.
19
How would you add OTP-based login for an Indian mobile app?
Generate a random 6-digit OTP with crypto.randomInt, store only its hash in Redis with a 5-minute TTL and an attempt counter, and send it through an SMS provider on a DLT-registered template. Verify with a timing-safe compare, limit to about 3 to 5 attempts and rate limit sends per number and IP. On success, issue access and refresh tokens and delete the OTP.
20
Tell me about a time a database change caused an issue and what you learned.
Situation: I added a NOT NULL column with a default to a large MySQL table during business hours. Task: the migration locked the table and checkout slowed down. Action: I rolled back, rewrote it as add nullable column, backfill in batches, then add the constraint, and ran it at low traffic after testing on a production-size copy. Result: no downtime, and we added a migration review checklist.
21
Explain ACID properties of a database transaction.
Atomicity means all operations in a transaction succeed or none do. Consistency means the database moves from one valid state to another, respecting constraints. Isolation means concurrent transactions do not see each other's partial work, controlled by isolation levels. Durability means committed data survives crashes. Money transfers rely on ACID so a debit never happens without the matching credit.
const cluster = require('cluster');
const os = require('os');
if (cluster.isPrimary) {
for (let i = 0; i < os.availableParallelism(); i++) cluster.fork();
cluster.on('exit', (worker) => {
console.log(`Worker ${worker.process.pid} died, restarting`);
cluster.fork();
});
} else {
require('./server'); // each worker listens on the same port
}
// In Kubernetes, prefer one process per container and more replicas.
Situation: customers occasionally received two invoices. Task: I had to find why it happened only in production. Action: I added request IDs to logs and found a forEach with async callbacks plus a retry triggering a second save before the first finished. I replaced it with for...of, added a unique index on invoice number and made the job idempotent. Result: duplicates stopped completely.
26
What is the difference between process.nextTick and setImmediate?
process.nextTick queues a callback to run immediately after the current operation, before the event loop continues to any phase, even before promise microtasks. setImmediate queues a callback for the check phase of the next loop iteration. Overusing nextTick recursively can starve I/O because the loop never moves on, so setImmediate is safer for deferring heavy work.
27
Convert this callback-based function to async/await: fs.readFile(path, 'utf8', (err, data) => {...}).
I use a layered structure: routes define endpoints, controllers handle HTTP details, services hold business logic, and repositories or models talk to the database. Add middlewares, validators, config and utils folders, and group by feature, for example modules/orders, once the app grows. This keeps controllers thin, makes services unit-testable and avoids business rules leaking into routes.
30
A teammate uses fs.readFileSync inside an Express route. What is the problem and what would you suggest?
Synchronous file calls block the event loop for the whole read, so under load every request queues behind disk I/O and latency spikes. In a route, use fs.promises.readFile with await, or stream the file with fs.createReadStream and pipe it to the response. Sync calls are acceptable only at startup, for example reading a config file once before the server listens.
31
Your Express API needs to support multiple client apps with different rate limits. How would you design it?
Identify the client through an API key or OAuth client ID in authentication middleware and attach the plan to req. Then use express-rate-limit or a custom limiter with a Redis store, keyed by client ID, with limits read from the plan. Return 429 with Retry-After and RateLimit headers. Redis keeps limits consistent across multiple server instances.
32
How do you manage database schema migrations in a Node.js project?
Use a migration tool such as Prisma Migrate, Knex, Sequelize CLI or TypeORM migrations, and commit migration files to Git. Each migration has up and ideally down steps and runs in CI and before deployment. For zero downtime, use expand and contract: add new columns first, deploy code that writes both, backfill, switch reads, then drop old columns in a later release.
An async function always returns a promise. await pauses that function until the awaited promise settles, then resumes it with the value or throws the rejection, while the event loop keeps running other work. Internally it is built on promises and generator-like suspension. The code reads like synchronous code but is still non-blocking, and errors are handled with ordinary try/catch.
34
A test passes locally but fails randomly in CI. How do you approach this flaky test?
Run it repeatedly to reproduce, then look for shared state between tests, missing awaits, reliance on test order, real timers, current date or time zones, random data and network calls. Fix by isolating data per test, using fake timers, freezing dates, mocking external calls and awaiting all promises. Quarantine the test only temporarily with a ticket, never delete it silently.
35
Tell me about an API you designed that you are proud of.
Situation: our support team used spreadsheets to track refunds. Task: I designed a refund API used by the admin panel and payment service. Action: I wrote the OpenAPI spec first, reviewed it with frontend and finance, added idempotency keys, clear error codes and pagination, and wrote contract tests. Result: integration took two days instead of a week, and refund errors dropped sharply.
Use multer for multipart/form-data. Configure limits for file size and count, filter allowed MIME types and extensions, and store files with generated names, not user-supplied names. For production, stream uploads directly to object storage such as S3 using presigned URLs so files do not pass through or fill the server disk. Scan files and never execute uploaded content.
Few big employers listed in Visakhapatnam?
Many Visakhapatnam candidates also apply to teams in Hyderabad and to remote or hybrid roles. Practise the Hyderabad set as well.
Which companies hire Full Stack with Node.js professionals in Visakhapatnam?
Companies with large offices in Visakhapatnam include many IT services and product firms. Use their company pages below to practise employer-specific sets.
Are Full Stack with Node.js interviews in Visakhapatnam different from other cities?
The questions depend more on the company than the city. Visakhapatnam's mix of employers decides the style: Many local candidates also apply to Hyderabad and remote roles, so a mix of service and product styles is common
How do I find Full Stack with Node.js jobs in Visakhapatnam?
Shortlist companies with Visakhapatnam offices, keep your CV focused on Full Stack with Node.js projects, apply on company career pages and job portals with the Visakhapatnam filter, and practise the questions on this page before each interview.