Curated interview practice questions with answers. These are practice scenarios, not a verified list of past interview questions.
About HCLTech hiring for MEAN Stack roles
HCLTech is an Indian multinational IT services and consulting company providing digital engineering, cloud, infrastructure, software products and data services. It works with clients in sectors such as financial services, manufacturing, life sciences and telecom. In India it hires for software engineers, test engineers, data analysts and data engineers through campus drives and programmes like TechBee.
For MEAN Stack roles, this HCLTech practice set focuses most on TypeScript and Modern JavaScript (6), Angular Components and Templates (5), RxJS, Signals and State Management (4), MongoDB Data Modelling and Queries (4). It has 17 easy, 12 medium, 1 hard questions, so you can start easy and work up to the harder ones.
Company type
IT services
Headquarters
Noida, India
Main India offices
Noida, Chennai, Bengaluru, Hyderabad, Lucknow
HCLTech MEAN Stack interview process
Online assessment (aptitude + technical)
Technical interview
Managerial round
HR round
Typical pattern based on public candidate experiences. Rounds vary by role, team and year.
Solved for HCLTechStart practicing
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01
Angular calls the Express API on a different port during development and gets CORS errors. What are your options?
In development, the cleanest fix is an Angular dev server proxy: a proxy.conf.json mapping /api to http://localhost:3000, so the browser sees same-origin requests. Alternatively enable the cors middleware in Express with the Angular origin allowed. In production, serve both under one domain through Nginx or configure CORS with an explicit allowlist, enabling credentials only when cookies are used.
02
Which security measures should every Express API in a MEAN app have?
Use HTTPS, helmet for security headers, a strict CORS allowlist, input validation on every route, rate limiting on auth endpoints, body size limits, parameterised queries and stripped MongoDB operators, bcrypt for passwords, secrets in environment variables, and least-privilege database users. Keep dependencies updated with npm audit or Dependabot, log security events and never return stack traces in production.
03
Create a counter component with signal, computed and effect.
Implement a type-ahead search box that calls the API only after the user pauses typing and ignores outdated results. Which RxJS approach would you use?
Take the input stream from a FormControl's valueChanges or toObservable of a signal, then pipe debounceTime(300) to wait for a pause, map to trimmed text, filter out terms shorter than two characters, distinctUntilChanged to skip repeats, and switchMap to call the API, which cancels any in-flight request when a new term arrives. Add catchError inside switchMap so one failed request does not kill the stream.
05
Write Mongoose queries to filter, sort, paginate and select fields for a products listing.
Send a FormData body with HttpClient post and options reportProgress: true and observe: 'events'. Filter the event stream for HttpEventType.UploadProgress to calculate percent from loaded and total, and for HttpEventType.Response to get the final result. Show a progress bar bound to a signal, allow cancelling by unsubscribing, and validate size and type before upload. For very large files, upload directly to storage with pre-signed URLs.
07
A teammate uses any everywhere to silence TypeScript errors. How would you address it?
Explain that any hides real bugs and removes autocompletion, then show concrete fixes: proper interfaces for API models, unknown with narrowing for untrusted data, and generics for reusable helpers. Enable the noImplicitAny compiler option and the ESLint no-explicit-any rule as a warning, fix the most critical files first, and add a review guideline. Keep the conversation constructive by pairing on one module together.
08
What is Angular and how is it different from a library like React?
Angular is a complete, opinionated front-end framework maintained by Google for building single-page applications in TypeScript. It includes routing, forms, an HTTP client, dependency injection, testing tools and a CLI out of the box, so teams follow a consistent structure. React is a UI library and relies on third-party choices for routing and state. Angular's structure suits large enterprise teams and long-lived projects.
09
What are decorators in TypeScript and how does Angular use them?
Decorators are functions that attach metadata or behaviour to classes, properties, methods or parameters using the @ syntax. Angular uses them to mark classes as framework building blocks: @Component, @Directive, @Pipe and @Injectable, along with property decorators like @Input, @Output, @ViewChild and @HostListener. Angular's compiler reads this metadata at build time to generate efficient rendering and dependency injection code.
10
What are signals in Angular and why were they introduced?
A signal is a reactive value container: you read it by calling it, count(), and update it with set or update. Angular tracks which templates, computed values and effects read a signal, so when it changes only dependent parts update. Signals give fine-grained reactivity, enable zoneless change detection and are simpler than RxJS for synchronous component state. They are stable and central to modern Angular.
11
Write a group validator that checks password and confirm password match.
Pipes transform values in templates, such as {{ price | currency:'INR' }}, date, uppercase, json and async. A pure pipe, the default, runs only when its input reference or primitive value changes, so it is very efficient. An impure pipe runs on every change detection cycle, which can hurt performance, and is needed only when output depends on mutable data. Prefer pure pipes or computed signals.
13
How do parent and child components communicate in Angular?
A parent passes data down through inputs, declared with the input() function or the @Input decorator, and the child notifies the parent through outputs, declared with output() or @Output with an EventEmitter. For two-way binding, model() creates a writable input. A parent can access a child directly using viewChild. For unrelated components, use a shared service holding a signal or a BehaviorSubject.
14
Write an exhaustive switch over a union type using never.
The never check makes the compiler flag unhandled cases.
type Shape = { kind: 'circle'; r: number } | { kind: 'square'; side: number };
function area(s: Shape): number {
switch (s.kind) {
case 'circle':
return Math.PI * s.r ** 2;
case 'square':
return s.side ** 2;
default: {
const unreachable: never = s;
throw new Error(`Unknown shape ${unreachable}`);
}
}
}
Adding a triangle variant now causes a compile error until it is handled.
15
What are generics in TypeScript? Give an Angular-related example.
Generics let you write reusable code that works with many types while keeping type safety, using type parameters like T. For example, an ApiResponse<T> interface can wrap any payload, and a service method get<T>(url: string): Observable<T> returns correctly typed data. Angular's HttpClient.get<User[]>() uses generics so the component knows it receives an array of users, without casting.
16
Write a custom pure pipe that shortens long text with an ellipsis.
ngOnChanges runs when input values change. ngOnInit runs once after the first inputs are set, used for initial data loading. ngDoCheck allows custom change detection. ngAfterContentInit and ngAfterViewInit run after projected content and the view are ready, used for DOM access. ngOnDestroy runs before removal, used for cleanup. With signals, effect, computed and DestroyRef often replace several of these hooks.
18
Why does Angular use TypeScript, and what benefits does it bring to a MEAN project?
TypeScript is a typed superset of JavaScript that compiles to plain JavaScript. Angular is written in TypeScript and relies on its types and decorators for components, dependency injection and templates. Types catch mistakes at compile time, improve editor autocompletion and make refactoring large codebases safer. In MEAN projects, you can share interfaces such as User or Order between the Express API and the Angular client.
19
What query and comparison operators do you use most in MongoDB?
Comparison operators include $eq, $ne, $gt, $gte, $lt, $lte, $in and $nin, for example { price: { $gte: 500, $lte: 2000 } }. Logical operators are $and, $or, $not and $nor. Element operators $exists and $type check fields, $regex matches patterns, and array operators $all, $size and $elemMatch query inside arrays. Projections choose returned fields, and sort, skip and limit shape the result.
20
What is middleware in Express, and what kinds of middleware are there?
Middleware is a function with access to req, res and next that runs in order for matching requests. Kinds include application-level middleware registered with app.use, router-level middleware on an express.Router, built-in middleware like express.json and express.static, third-party middleware such as cors, helmet and morgan, and error-handling middleware with four arguments. Middleware can end the response or pass control with next().
21
Build a reactive login form with validation using NonNullableFormBuilder.
providedIn: 'root' registers the service with the application's root injector, so one shared instance exists and it is tree-shakable, meaning it is removed from the bundle if unused. You can also provide services in a component's providers array, giving each component instance its own copy, in a route's providers for a lazy feature, or in app.config.ts. The provider location decides scope and lifetime.
23
How do you set up an Express project with TypeScript?
Install express and types with npm i express and npm i -D typescript @types/express @types/node. Create a tsconfig with strict mode and a module setting like NodeNext, write code in src and compile to dist with tsc. For development, run TypeScript directly with tsx watch, and use node dist/server.js in production. Type request bodies, params and responses with Request and Response generics or validated schemas.
24
How do you test Express APIs and MongoDB logic in a MEAN project?
Write unit tests for services with Jest or Vitest, mocking external providers. For integration tests, use Supertest to send requests to the exported Express app and mongodb-memory-server or a disposable Docker MongoDB for realistic queries, seeding and cleaning data around each test. Test validation errors, auth failures and permissions, not only happy paths. Run tests in CI on every pull request.
25
An npm audit shows several high-severity vulnerabilities in the Express project. How do you handle it?
Read each advisory to see whether the vulnerable code path is actually used in production or only in dev tooling. Run npm audit fix for safe updates, upgrade direct dependencies that pull vulnerable transitive packages, and use overrides in package.json if a fix is not yet released upstream. Test thoroughly after upgrading, enable Dependabot or Renovate for continuous updates and track any accepted risks.
Narrowing is TypeScript refining a broad type to a more specific one inside a code block based on checks. typeof, instanceof, the in operator, equality checks and discriminated union tags all narrow types. A custom type guard is a function returning a predicate like value is Admin, which tells the compiler the type after the check. This makes handling union types, such as API success or error responses, safe.
$lookup performs a left outer join with another collection in the same database. The basic form matches localField to foreignField and writes matching documents into an array field. The pipeline form lets you add conditions, filtering and projections on the joined collection using let variables. Often you follow it with $unwind to flatten the array. Index the foreign field so the join stays efficient.
28
Write mongosh commands to inspect a slow query and the indexes on a collection.
signal() creates writable state. computed() derives a read-only value from other signals, is lazily evaluated and memoised, and recalculates only when its dependencies change, for example a cart total from cart items. effect() runs side effects whenever signals it reads change, such as logging or syncing to local storage. Use computed for derived data and keep effects for non-UI side effects, not for setting other state.
30
A registration form must check that password and confirm password match. How would you implement this?
Add a cross-field validator at the FormGroup level, because a single control cannot see the other field. The validator reads both values and returns { passwordMismatch: true } when they differ. Show the error under the confirm field when the group has the error and the field is touched. Also validate password strength with a pattern or custom validator, and check it again on the Express backend.
Tips to crack the HCLTech MEAN Stack interview
Revise programming basics, SQL and networking fundamentals, as HCLTech roles span applications and infrastructure services.
Learn about HCLTech's software products business, HCLSoftware, and its engineering and R&D services.
Be clear and honest about your preferred domain and shift flexibility, as some roles involve support or global time zones.
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; HCLTech interviewers usually ask follow-ups on your first answer.
Frequently asked questions
How many rounds are there in the HCLTech MEAN Stack interview?
Candidates usually go through 4 stages: Online assessment (aptitude + technical); Technical interview; Managerial round; HR round. 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 HCLTech MEAN Stack interview?
This practice set leans on TypeScript and Modern JavaScript (6), Angular Components and Templates (5), RxJS, Signals and State Management (4), MongoDB Data Modelling and Queries (4). Revise those first, then practise explaining one or two of your own projects end to end, because most HCLTech interviewers ask you to walk through real work.
Are these the exact questions asked at HCLTech?
No. These are curated practice questions that match the skills and difficulty usually tested in it services interviews like HCLTech's. They are not a leaked or verified list of past questions.
Where does HCLTech hire MEAN Stack professionals in India?
HCLTech has large teams in Noida, Chennai, Bengaluru, Hyderabad, Lucknow. Openings and locations change often, so check the HCLTech careers page and filter by city and experience.