Curated interview practice questions with answers. These are practice scenarios, not a verified list of past interview questions.
About Accenture hiring for MERN Stack roles
Accenture is a global professional services company offering strategy, consulting, technology, operations and digital services. India hosts a large share of its workforce, delivering software engineering, testing, cloud, data and AI projects for clients worldwide. It hires freshers and experienced professionals in India for associate software engineer, test engineer, data analyst and analytics consultant roles.
For MERN Stack roles, this Accenture practice set focuses most on MongoDB and Mongoose (6), Node.js Core (6), Authentication and Security (5), Testing, Deployment and DevOps (4). It has 8 easy, 20 medium, 2 hard questions, so you can start easy and work up to the harder ones.
Company type
Consulting
Headquarters
Dublin, Ireland
Main India offices
Bengaluru, Hyderabad, Pune, Mumbai, Gurugram
Accenture MERN Stack interview process
Online assessment (cognitive + technical MCQs)
Coding assessment
Communication assessment
Technical and HR interview
Typical pattern based on public candidate experiences. Rounds vary by role, team and year.
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01
Your MERN app works on your laptop but crashes after deployment to a server. How do you troubleshoot?
Read the server logs first. Common causes are missing environment variables, a different Node version, the database host or IP allowlist blocking the server, hardcoded localhost URLs, wrong PORT handling, devDependencies missing in production, case-sensitive file names on Linux, and the frontend API base URL pointing to localhost. Reproduce with the same Node version or a Docker image, and validate config at startup.
02
What are a Mongoose schema and model, and how does validation work?
A schema defines the shape of documents: field types, defaults, required flags, validators, indexes and options like timestamps. A model is compiled from a schema with mongoose.model('User', userSchema) and provides query methods like find, create and updateOne. Built-in validators include required, min, max, enum and match, and you can add custom validators. Validation runs on save and create; for updates, set runValidators: true.
03
Compress a large file with gzip using streams in Node.js.
The user submits an email; always respond with the same message whether or not it exists. Generate a random token with crypto.randomBytes, store only its hash with an expiry of around 15 minutes, and email a link with the raw token. On submission, hash the token, find a matching unexpired record, set the new hashed password, delete the token and invalidate existing sessions. Rate limit the endpoint.
06
Tell me about a deployment that went wrong and what you learned.
Situation: a release broke login for all users because a new environment variable was missing in production. Task: restore service fast. Action: I rolled back to the previous version within ten minutes, added the variable, and redeployed after testing on staging. Afterwards I added startup config validation and a post-deploy smoke test for login in our pipeline. Result: no config-related outage has happened since.
When two or more components need the same data, you move that state to their closest common parent and pass it down as props, along with functions to update it. For example, a filter bar and a product list both depend on the selected category, so the page component holds the category state. This keeps one source of truth and avoids components getting out of sync.
08
Write an aggregation that counts orders and sums revenue per status.
Situation: our admin orders page took 8 seconds to load. Task: I was asked to fix it within a sprint. Action: I profiled the API, found a populate on every row plus an unindexed sort, added a compound index, replaced populate with a single $lookup projecting only needed fields, and used lean. Result: load time dropped below 600 ms and I shared an indexing checklist with the team.
10
What is the difference between CommonJS and ES modules in Node.js?
CommonJS uses require and module.exports, loads synchronously and is the historic Node default. ES modules use import and export, are statically analysable, support top-level await and enable tree shaking. Node treats .mjs files, or .js files when package.json has type: module, as ESM. Modern Node versions can even require synchronous ES modules, but mixing systems still needs care, so new MERN projects usually pick ESM throughout.
11
How do environment variables work in a Vite React app compared to a Node.js backend?
In Node, process.env is read at runtime on the server, so secrets are safe there. In a Vite app, only variables prefixed with VITE_ are exposed, through import.meta.env, and they are embedded into the JavaScript bundle at build time. Anything in the frontend bundle is public, so never put database passwords or secret keys there. Changing a frontend variable requires a rebuild.
12
Tell me about a time you received critical feedback on your UI code and how you responded.
Situation: in my internship, a senior reviewer rejected my pull request because my components were large and repeated logic. Task: fix it without missing the sprint deadline. Action: I asked for examples, split the page into smaller components, extracted a custom hook for the shared fetching logic and added prop types. Result: the PR was approved the next day, and the reviewer used my hook in another feature.
Streams process data in chunks instead of loading it all into memory. The four types are Readable (file read, HTTP request), Writable (file write, HTTP response), Duplex (TCP socket) and Transform (gzip, encryption), which modifies data as it passes. Streams handle backpressure, pausing the source when the destination is slow. pipeline() from node:stream/promises connects them safely and handles errors and cleanup.
14
How do class component lifecycle methods map to hooks?
componentDidMount maps to useEffect with an empty dependency array. componentDidUpdate maps to useEffect with specific dependencies. componentWillUnmount maps to the cleanup function returned from useEffect. shouldComponentUpdate is roughly React.memo, and getDerivedStateFromProps is usually replaced by computing values during render. The mindset shifts from lifecycle moments to synchronising with external systems whenever certain values change.
15
Tell me about a time you found and fixed a security issue in an application.
Situation: while testing an order history feature, I noticed changing the order id in the URL showed another user's order. Task: fix this insecure direct object reference before release. Action: I added an ownership check in the service layer so queries always filter by the logged-in user's id, wrote tests for cross-user access, and reviewed similar endpoints. Result: we fixed four endpoints and added ownership checks to our review checklist.
16
You are building a registration form with ten fields and validation. How do you manage its state?
For a simple form, keep a single state object and update fields with a shared handler using the input name, for example setForm({ ...form, [e.target.name]: e.target.value }). Validate on blur and submit, storing errors in another object. For larger forms, use React Hook Form with a zod schema, which reduces re-renders and shares the validation schema with the Express backend.
17
Compare offset-based and cursor-based pagination for an API.
Offset pagination uses page and limit, translating to skip and limit in MongoDB. It is simple and allows jumping to page 10, but gets slower on large collections and can skip or repeat items when data changes. Cursor pagination returns items after a stable sorted value, such as the last _id or createdAt, using an indexed range query. It stays fast and consistent, ideal for infinite scroll feeds.
18
What is a custom hook and what rules must hooks follow?
A custom hook is a function whose name starts with use and that calls other hooks to package reusable stateful logic, such as useFetch, useDebounce or useAuth. Each component using it gets its own state. Hooks must be called at the top level of a component or another hook, never inside conditions, loops or nested functions, so React can match state by call order. The eslint-plugin-react-hooks rules enforce this.
19
How would you structure the folders of a production Express API?
A layered structure keeps responsibilities clear: src/routes for route definitions, src/controllers for request and response handling, src/services for business logic, src/models for Mongoose schemas, src/middlewares for auth, validation and errors, src/config for environment and database setup, src/utils for helpers, and tests alongside or in a tests folder. Keep app.js, which builds the app, separate from server.js, which listens, so tests can import the app.
20
Your app needs user, editor and admin roles with different permissions. How would you implement it?
Store a role, or a list of permissions, on the user document and include it in the token or load it in the auth middleware. Write an authorize middleware that checks allowed roles or permissions per route, for example authorize('admin'). Add ownership checks in services, such as an editor editing only their own articles. In React, hide buttons by role for user experience, but always enforce rules on the server.
21
A MongoDB query on an orders collection takes 3 seconds. How do you diagnose and fix it?
Run the query with .explain('executionStats') and check whether the winning plan is COLLSCAN and how totalDocsExamined compares to nReturned. Create an index matching the filter and sort, following ESR, and confirm it becomes IXSCAN. Also project only needed fields, add limits, use lean in Mongoose, and check the profiler or Atlas Performance Advisor for other slow queries. Re-test with production-like data volume.
22
Users must upload files up to 200 MB. How would you handle this in a MERN application?
Avoid buffering big files in the API server's memory. The best approach is to have the backend generate a pre-signed URL for object storage such as S3, then let the React client upload directly to storage, with multipart upload for large files. If uploads must go through Express, use multer with disk storage or stream to storage, enforce size and type limits, and save only metadata in MongoDB.
23
Explain indexes in MongoDB, compound indexes and the ESR rule.
An index is a sorted structure that lets queries avoid scanning every document. A compound index covers multiple fields in order, like { userId: 1, createdAt: -1 }, and supports queries on its leading prefix. The ESR guideline says order fields as Equality first, then Sort, then Range. Indexes speed reads but slow writes and use memory, so create them for real query patterns and drop unused ones.
24
Your API becomes unresponsive whenever a user uploads an image for resizing. What is happening and how do you fix it?
Resizing is CPU-bound work running on the main thread, so it blocks the event loop and every other request waits. Fix it by moving the work off the main thread: use a worker_threads pool, a native library like sharp that works in the libuv pool, or better, push a job to a queue such as BullMQ with Redis and process it in a separate worker service, then notify the client.
25
Should you store a JWT in localStorage or in an httpOnly cookie?
localStorage is readable by any JavaScript on the page, so an XSS bug can steal the token. An httpOnly, Secure cookie cannot be read by JavaScript, which protects against token theft through XSS, but cookies are sent automatically, so you must defend against CSRF with SameSite=Lax or Strict and CSRF tokens where needed. A common pattern keeps the refresh token in an httpOnly cookie and the access token in memory.
26
Write a production Dockerfile for a Node.js Express API.
Keep the image small and run as a non-root user.
FROM node:22-alpine
WORKDIR /app
ENV NODE_ENV=production
COPY package*.json ./
RUN npm ci --omit=dev
COPY src ./src
USER node
EXPOSE 5000
CMD ["node", "src/server.js"]
Copying package files first lets Docker cache the dependency layer, so code changes rebuild quickly. Add a .dockerignore with node_modules and .env.
Keep config in environment variables, following the twelve-factor approach. Locally, load a .env file with dotenv or Node's built-in --env-file flag, and add .env to .gitignore while committing a .env.example. In production, inject variables through the hosting platform or a secrets manager. Validate all required variables at startup with a schema library like zod so the app fails fast with a clear message.
29
Your script crashes with out of memory while reading a 5 GB log file. How would you rewrite it?
fs.readFile loads the whole file into memory, which exceeds the heap. Use a stream instead: fs.createReadStream with readline lets you process one line at a time with for await, keeping memory flat. If you need to transform and write output, connect read, transform and write streams with pipeline so backpressure and errors are handled. Increasing --max-old-space-size only hides the real problem.
30
What practical steps do you take to sanitise and validate input in an Express and MongoDB API?
Validate every request body, params and query against a schema with zod or Joi, rejecting unknown fields and wrong types. Apply body size limits with express.json({ limit: '100kb' }). Strip MongoDB operator keys from input with a small sanitising middleware or library, and keep Mongoose strict mode on. Escape or sanitise HTML with DOMPurify before storing rich text, and validate ObjectIds before querying.
Tips to crack the Accenture MERN Stack interview
Practise the communication assessment, which checks spoken English through reading, listening and repeating sentences in a recorded format.
Revise MS Office, cloud basics, networking and pseudocode, as Accenture technical MCQs often cover these general IT topics.
Read about Accenture's focus on cloud, data and AI and be ready to discuss how you would work in client-facing teams.
Keep a one-minute story ready for every project on your CV: problem, your part, tools, result.
Practise the hard questions on this page aloud; Accenture interviewers usually ask follow-ups on your first answer.
Frequently asked questions
How many rounds are there in the Accenture MERN Stack interview?
Candidates usually go through 4 stages: Online assessment (cognitive + technical MCQs); Coding assessment; Communication assessment; Technical and HR interview. The exact rounds change with the role, team, location and your experience, so confirm the process with the recruiter.
Which topics should I prepare for the Accenture MERN Stack interview?
This practice set leans on MongoDB and Mongoose (6), Node.js Core (6), Authentication and Security (5), Testing, Deployment and DevOps (4). Revise those first, then practise explaining one or two of your own projects end to end, because most Accenture interviewers ask you to walk through real work.
Are these the exact questions asked at Accenture?
No. These are curated practice questions that match the skills and difficulty usually tested in consulting interviews like Accenture's. They are not a leaked or verified list of past questions.
Where does Accenture hire MERN Stack professionals in India?
Accenture has large teams in Bengaluru, Hyderabad, Pune, Mumbai, Gurugram. Openings and locations change often, so check the Accenture careers page and filter by city and experience.