Full Stack with Node.js Interview Questions in Nagpur
36 practice questions with answers for Full Stack with Node.js interviews in Nagpur.
Full Stack with Node.js jobs in Nagpur
Nagpur's MIHAN SEZ hosts IT-services and BFSI delivery centres, giving central India a steady market for data and QA roles. Interviews are usually service-company style, with aptitude, technical and HR rounds.
Below are 36 questions that match the mix of service, product and domain employers hiring node.js developers in Nagpur.
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01
How do you read a large file efficiently in Node.js?
const fs = require('fs');
const readline = require('readline');
async function countErrors(path) {
const rl = readline.createInterface({
input: fs.createReadStream(path),
crlfDelay: Infinity
});
let count = 0;
for await (const line of rl) {
if (line.includes('ERROR')) count++;
}
return count;
}
// Streams line by line, so a 5 GB log uses little memory.
Sessions store state on the server, often in Redis, and the client holds only a session ID cookie; logout and revocation are easy. JWTs are stateless, so any service can verify them without a lookup, which suits microservices and mobile apps, but revoking a token before expiry needs a denylist or short lifetimes. Many systems combine short-lived JWT access tokens with server-stored refresh tokens.
04
What is the difference between req.params, req.query and req.body?
req.params holds route parameters from the path, such as id in /users/:id. req.query holds query string values like ?page=2&sort=name, used for filtering and pagination. req.body holds the parsed request payload of POST, PUT or PATCH and needs a parser such as express.json(). All are user input and must be validated before use.
05
Tell me about a time you improved code quality in a backend codebase you inherited.
Situation: I joined a project where Express routes contained SQL, business logic and responses in 300-line handlers. Task: reduce bugs without stopping feature work. Action: I proposed a controller-service-repository structure, added an error handler, validation with zod and tests for each refactored route, and moved one module per sprint. Result: bug reports dropped and new developers onboarded faster.
06
A scheduled job processes orders with setInterval every minute, but sometimes runs overlap and duplicate emails are sent. How do you fix it?
setInterval fires regardless of whether the previous async run finished. Use a recursive setTimeout that schedules the next run only after the current one completes, or keep an isRunning flag. If several instances run, use a distributed lock in Redis or a job queue like BullMQ with unique job IDs. Also make email sending idempotent by recording sent message IDs.
07
How do you handle a situation where you cannot find the root cause of a bug before a deadline?
I inform my lead early with what I know, what I have ruled out and the risk. I propose a safe mitigation, such as a feature flag to disable the path or a rollback, and add extra logging to capture more data. In one case this let us release on time with the feature off, and the new logs revealed the cause two days later.
08
Write a simple request logging middleware that records response time.
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.
09
Implement cursor-based pagination for a products endpoint.
Options include virtual machines like EC2 with PM2 and Nginx, containers on Kubernetes such as EKS, AKS or GKE, managed container services like AWS ECS Fargate, Cloud Run or Azure Container Apps, platforms like Render or Railway, and serverless functions on AWS Lambda. Choice depends on traffic patterns, team skills, cost and need for control.
Mongoose is an ODM for MongoDB in Node.js. It adds schemas with types, validation, defaults, middleware hooks such as pre save, virtuals, population of references and a convenient query API. This brings structure to schemaless MongoDB collections and reduces bugs. For very high-performance or simple cases, some teams use the native MongoDB driver directly to avoid the overhead.
PUT replaces the entire resource with the representation sent, so missing fields may be reset; it is idempotent. PATCH applies a partial update, sending only changed fields, such as { "phone": "..." }. PATCH is more efficient for large objects. With JSON Merge Patch, repeated identical PATCH requests are effectively idempotent, but operations like increment are not.
13
Users report seeing stale prices after an update because of caching. How do you solve it?
Invalidate or update the cache key in the same code path that updates the price, preferably after the database commit. Use reasonable TTLs as a safety net, and version keys if needed. If several services update prices, publish a price-changed event and have consumers delete the cache. For CDN-cached responses, purge the relevant URLs or use short max-age with stale-while-revalidate.
14
What is the difference between CommonJS and ES Modules in Node.js?
CommonJS uses require and module.exports, loads modules synchronously and was Node's original system. ES Modules use import and export, are statically analysable, support top-level await and are the JavaScript standard. In Node you enable ESM with the .mjs extension or "type": "module" in package.json. ESM can import CommonJS, but CommonJS needs dynamic import() to load ESM in older versions.
15
How do you enable CORS in an Express app and why is it needed?
Browsers block cross-origin requests unless the server sends CORS headers. Use the cors package: app.use(cors({ origin: ['https://app.example.com'], credentials: true })). Avoid origin '*' with credentials, and restrict methods and headers you allow. CORS is a browser protection, not a security layer for your API, so you still need authentication and authorisation.
16
What metrics would you monitor for a Node.js API in production?
Use the RED method for requests: rate, errors and duration with p50, p95 and p99. Add Node-specific metrics: event loop lag, heap used, garbage collection time and active handles, plus CPU, memory and restarts. Monitor dependencies such as database query time, pool usage and cache hit ratio. Export with prom-client or OpenTelemetry and alert on symptoms users feel.
17
Tell me about a production incident you handled and what you did after it.
Situation: our payment callback endpoint started failing after a deploy on a Friday evening. Task: I was on call. Action: I checked error logs, saw a missing environment variable, rolled back within ten minutes, then added startup config validation and a post-deploy smoke test. Result: impact was limited to a few failed callbacks we replayed, and I wrote a blameless postmortem the team used to improve deploy checks.
Add field selection like ?fields=id,name,price, smaller list representations with details on a separate endpoint, pagination with sensible limits and gzip or Brotli compression. Support ETag and Cache-Control so unchanged data returns 304. If many screens need combined data, consider a Backend-for-Frontend layer or GraphQL tailored to the mobile app.
20
What is the OWASP Top 10 and which items matter most for Node.js APIs?
The OWASP Top 10 lists the most critical web application security risks. For Node APIs the most relevant are broken access control, injection, cryptographic failures, security misconfiguration, vulnerable and outdated components, authentication failures and server-side request forgery. OWASP also publishes an API Security Top 10, which highlights broken object level authorisation, where users access others' data by changing an ID.
21
Write a Jest unit test for a function that calculates order total with GST.
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.
23
What happens if you forget to await a promise inside a try/catch?
If you call an async function without await, the try/catch only covers the synchronous part, so a later rejection escapes it and becomes an unhandled rejection that can crash the process. The function also continues before the work finishes, causing race conditions like responding before data is saved. ESLint rules such as no-floating-promises in TypeScript help catch this.
24
What is the difference between app.use and app.get?
app.use mounts middleware for all HTTP methods and matches any path that starts with the given prefix, for example app.use('/api', router). app.get registers a handler only for GET requests on an exact route pattern. Use app.use for cross-cutting concerns like parsing and auth, and method-specific functions such as get, post, put and delete for endpoints.
25
What are the common strategies for API versioning?
URL versioning like /api/v1/orders is the most common and easy to route and cache. Header versioning uses a custom header or Accept media type, keeping URLs clean but less visible. Query versioning like ?version=2 is simple but messy. Whatever you choose, version only for breaking changes, support old versions for a deprecation period and announce sunset dates.
26
How do you limit concurrency when calling an external API for 10,000 records?
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.
28
Is Node.js single-threaded? Explain the role of libuv.
Your JavaScript runs on a single main thread, but Node.js itself is not purely single-threaded. libuv, the C library under Node, provides the event loop and a thread pool (default 4 threads, set with UV_THREADPOOL_SIZE) used for file system work, DNS lookups, crypto and zlib. Network I/O uses OS async mechanisms like epoll or IOCP instead of threads.
29
When should you embed documents versus reference them in MongoDB?
Embed when data is read together, owned by the parent and bounded in size, such as addresses inside a user or line items inside an order. Reference when the related data is large, grows without limit, is shared across many documents or changes independently, such as products referenced by orders or comments on a viral post. Remember the 16 MB document size limit.
30
How do you implement rate limiting on a login endpoint?
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.
33
Explain the Node.js event loop and its main phases.
The event loop lets Node.js run asynchronous callbacks on a single thread. Each iteration passes through phases: timers (setTimeout, setInterval), pending callbacks, poll (waits for and runs I/O callbacks), check (setImmediate), and close callbacks. Between phases Node drains the process.nextTick queue and the promise microtask queue. Understanding phases explains why setImmediate runs before a 0 ms timer inside an I/O callback.
34
What is the difference between throwing an error and rejecting a promise inside an async function?
Inside an async function they behave the same: throw new Error() causes the returned promise to reject with that error. Outside async functions, a throw inside a plain callback such as setTimeout is not caught by promise handlers and becomes an uncaught exception. Always reject with Error objects, not strings, so you keep a stack trace.
35
Describe how you would mentor a junior developer who writes no tests.
I would start by understanding why: lack of time, knowledge or examples. Then I pair with them on one feature, writing a test first for a real bug so they see the value. I share a small template for service and route tests, review their tests kindly in pull requests and celebrate when a test catches a regression. Over a few sprints, testing becomes a habit.
36
Explain semantic versioning and the meaning of ^ and ~ in package.json.
Semantic versioning uses MAJOR.MINOR.PATCH: major for breaking changes, minor for new backward-compatible features, patch for bug fixes. A caret like ^4.18.2 allows any 4.x.x at or above 4.18.2. A tilde like ~4.18.2 allows only patch updates, 4.18.x. An exact version pins it. The lock file still decides what is actually installed.
Few big employers listed in Nagpur?
Many Nagpur candidates also apply to teams in Pune and to remote or hybrid roles. Practise the Pune set as well.
Which companies hire Full Stack with Node.js professionals in Nagpur?
Companies with large offices in Nagpur 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 Nagpur different from other cities?
The questions depend more on the company than the city. Nagpur's mix of employers decides the style: Interviews are usually service-company style, with aptitude, technical and HR rounds
How do I find Full Stack with Node.js jobs in Nagpur?
Shortlist companies with Nagpur offices, keep your CV focused on Full Stack with Node.js projects, apply on company career pages and job portals with the Nagpur filter, and practise the questions on this page before each interview.