Full Stack with Node.js Interview Questions in Coimbatore
36 practice questions with answers for Full Stack with Node.js interviews in Coimbatore.
Full Stack with Node.js jobs in Coimbatore
Coimbatore has a growing IT-services and engineering-services market around TIDEL Park and its SEZs, supported by a large pool of engineering graduates. Many roles are with delivery centres of bigger IT firms.
Below are 36 questions that match the mix of service, product and domain employers hiring node.js developers in Coimbatore.
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01
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most relevant are broken access control, injection, cryptographic failures, security misconfiguration, vulnerable and outdated components, authentication failures and server-side request forgery.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.
First check whether the vulnerable code path is actually reachable in our usage and read the advisory. Try npm audit fix or updating the parent package to a version that pulls a patched sub-dependency. If none exists, use the overrides field in package.json to force a safe version and run tests. Track it in a ticket and enable Dependabot or Renovate for ongoing updates.
04
What is package-lock.json and why should it be committed?
package-lock.json records the exact resolved version and integrity hash of every installed package, including nested ones. Committing it makes installs reproducible across developer machines and CI, so a minor update in a transitive dependency cannot silently break production. In CI use npm ci, which installs strictly from the lock file and fails if it is out of sync with package.json.
Buffer represents a fixed-length sequence of raw bytes stored outside the V8 heap. It is used for binary data such as files, images, TCP packets and crypto output. You create one with Buffer.from('text') or Buffer.alloc(size) and convert with toString('utf8' or 'base64'). Buffer.allocUnsafe is faster but may contain old memory, so fill it before use.
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.
09
Implement cursor-based pagination for a products endpoint.
When a hot key expires, thousands of requests may hit the database at once. Solutions: allow only one request to rebuild the cache using a short Redis lock while others wait or serve stale data, refresh hot keys in the background before expiry, add random jitter to TTLs so keys do not expire together, and use stale-while-revalidate where slightly old data is acceptable.
11
How do you run integration tests against a real database in CI?
Start a disposable database for the test run, using Docker Compose services in CI, Testcontainers from the test code, or mongodb-memory-server for MongoDB. Run migrations before tests, seed minimal data per test, and clean tables between tests or wrap each test in a rolled-back transaction. Use a separate DATABASE_URL so tests can never touch production data.
12
How do you implement rate limiting on a login endpoint?
Normalisation organises tables to remove duplicate data and update anomalies, typically up to third normal form, for example keeping customers and orders in separate tables linked by foreign keys. You denormalise for read performance, such as storing a product name on an order line or a precomputed order count on a user, when joins become expensive. Denormalised data must be kept in sync.
14
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.
15
What is connection pooling and why is it important in Node.js?
Opening a database connection is slow, so a pool keeps a set of open connections that requests borrow and return. pg Pool, mysql2 and the MongoDB driver all pool by default. Size the pool based on database limits and instance count; too small causes waiting, too large overloads the database. In serverless functions, reuse the client across invocations or use a proxy like RDS Proxy.
16
Memory usage of a Node.js service grows steadily until the pod restarts. How would you find the leak?
First confirm with metrics that heap used keeps rising under steady traffic. Take heap snapshots with --inspect and Chrome DevTools or heapdump at intervals and compare them to find objects whose count keeps growing. Common causes are global caches without limits, event listeners added per request, closures holding large objects and unclosed timers. Fix, then load test with autocannon to verify heap stabilises.
17
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.
18
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.
19
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.
20
How do you serve a React build and an API from the same Express server?
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.
EventEmitter from the events module implements the publish-subscribe pattern. Objects register listeners with on or once and trigger them with emit. Streams, HTTP servers and sockets all extend it. Always handle the 'error' event, because an emitted error without a listener crashes the process. Watch for memory leaks when listeners are added repeatedly; Node warns after 10 listeners by default.
Never store plain text or use fast hashes like MD5 or SHA-256 alone. Use a slow, salted password hashing algorithm such as bcrypt with a cost factor around 10 to 12, or Argon2id, which is the current recommendation. The library generates a unique salt per password. On login, compare using the library's compare function, which is timing-safe.
23
How do you enable compression and why should you be careful with it?
Use the compression middleware or, better, let Nginx or the CDN compress responses with gzip or Brotli, which reduces JSON payload size by 70 percent or more. Be careful: compressing in Node uses CPU on the event loop, small responses gain little, and already compressed files like images should be skipped. Never compress responses mixing secrets with user input over HTTPS because of BREACH-style attacks.
24
What is package.json and what is the difference between dependencies and devDependencies?
package.json describes a project: name, version, scripts, entry point and dependencies. dependencies are packages needed at runtime, such as express or mongoose. devDependencies are only for development and build, such as jest, eslint or nodemon. Running npm ci --omit=dev in production installs only runtime packages, which keeps Docker images smaller and reduces attack surface.
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.
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.
27
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.
28
How do you manage configuration for dev, staging and production environments?
Follow the twelve-factor approach: keep config in environment variables, not code. Load and validate them at startup with a schema, for example zod or envalid, and fail fast if any are missing. Use .env files only locally, and store production values in the platform's secret store or config maps. Keep the same Docker image across environments and change only configuration.
29
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.
30
Write a centralised error handler with a custom AppError class.
Nginx acts as a reverse proxy: it terminates TLS, serves static files efficiently, compresses responses, buffers slow clients, load balances across multiple Node instances and adds rate limiting and request size limits. This frees Node to focus on application logic. On cloud platforms a managed load balancer or ingress controller often plays the same role.
32
An API listing orders became slow after the table reached 50 million rows. How do you investigate?
Run EXPLAIN ANALYZE on the slow query to see whether it does a sequential scan or a costly sort. Add a composite index matching the filter and sort, for example (user_id, created_at DESC). Replace OFFSET pagination with cursor pagination, select only needed columns, and consider partitioning by date and archiving old rows. Monitor slow query logs after the change.
33
Explain the difference between Promise.all, Promise.allSettled, Promise.race and Promise.any.
Promise.all resolves with all results when every promise fulfils, and rejects as soon as one rejects. Promise.allSettled waits for all and returns each status and value or reason, useful when partial failure is fine. Promise.race settles with the first promise to settle, often used for timeouts. Promise.any resolves with the first fulfilled promise and rejects only if all reject.
34
How do you implement filtering and sorting safely from query parameters?
Debounce runs a function only after calls stop for a set time, merging bursts into one call. Throttle runs it at most once per interval. On the backend they help when batching cache invalidation, limiting webhook processing, writing metrics, or reacting to file watcher events. For API traffic you normally use a rate limiter instead, which is a server-side form of throttling.
36
How do you design a consistent error response format for an API?
Use one structure everywhere, for example { "error": { "code": "VALIDATION_FAILED", "message": "Email is invalid", "details": [{ "field": "email" }], "requestId": "abc123" } }. Many teams follow RFC 9457 Problem Details with type, title, status and detail. Use machine-readable codes for clients, human messages for display, and never leak stack traces or SQL errors.
Few big employers listed in Coimbatore?
Many Coimbatore candidates also apply to teams in Chennai and to remote or hybrid roles. Practise the Chennai set as well.
Which companies hire Full Stack with Node.js professionals in Coimbatore?
Companies with large offices in Coimbatore 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 Coimbatore different from other cities?
The questions depend more on the company than the city. Coimbatore's mix of employers decides the style: Many roles are with delivery centres of bigger IT firms
How do I find Full Stack with Node.js jobs in Coimbatore?
Shortlist companies with Coimbatore offices, keep your CV focused on Full Stack with Node.js projects, apply on company career pages and job portals with the Coimbatore filter, and practise the questions on this page before each interview.