Interview questions and answers for freshers

Common interview questions for freshers and first-job seekers, with a model answer for each and answers shared by other job seekers.

Fresher questions · Experienced questions · Salaries · Company reviews

Angular HTTP, RxJS and state

• How do you call an API in Angular?
• What is an Observable, and how is it different from a Promise?
• What is the difference between subscribe and the async pipe?
• What are common RxJS operators you use, and what do they do?
• Explain the difference between switchMap, mergeMap, concatMap and exhaustMap.
• What are HTTP interceptors, and what are they used for?
• How do you handle errors from HTTP calls?
• How do you prevent memory leaks from subscriptions?
• What are Subject, BehaviorSubject and ReplaySubject, and when would you use each?

Angular basics

• What is Angular, and how is it different from AngularJS?
• What is a single-page application (SPA)?
• What does the Angular CLI do? Name some common commands.
• What is a standalone component, and why did Angular move away from NgModules?
• What is TypeScript, and why does Angular use it?
• Describe the structure of a basic Angular project.
• What happens when an Angular application starts?
• What is the difference between a component and a service?
• What is a decorator in Angular? Name a few.
• What is dependency injection, and why is it useful?
• How do you create and use a service?
• What is the difference between ng serve and ng build?

Angular components and templates

• What are the parts of a component?
• What is data binding? Explain the four types.
• What is the difference between interpolation and property binding?
• How do you pass data from a parent component to a child component?
• How does a child component send data to its parent?
• What is the component lifecycle? Describe the main hooks.
• What is the difference between the constructor and ngOnInit?
• What is ViewEncapsulation?
• What are template reference variables?
• How does content projection (ng-content) work?
• What do @if, @for and @switch do, and why was this syntax added?

Angular directives, pipes and DI

• What is a directive? What are the types?
• What is the difference between ngClass and ngStyle, and how do they compare with class and style bindings?
• What is a pipe? Name some built-in pipes.
• How do you create a custom pipe? What is the difference between pure and impure pipes?
• What does the async pipe do, and why is it recommended?
• How do you build a custom attribute directive?
• What is the difference between providedIn root and providing a service in a component?
• What is the inject() function, and how does it compare with constructor injection?
• What are injection tokens, and when would you use InjectionToken?

Angular forms

• What is the difference between template-driven and reactive forms?
• How do you add validation to a reactive form?
• How do you write a custom validator?
• What are async validators and when do you need one?
• What are FormArray and dynamic forms?
• What is the difference between valueChanges and statusChanges, and how do you use them safely?
• What do touched, dirty and pristine mean?
• How do you submit a reactive form and reset it afterwards?

Angular performance and SSR

• Why is track important in @for (or trackBy in *ngFor)?
• What are the main ways to improve Angular app performance?
• Why is calling a method in a template expression a performance problem?
• What is NgOptimizedImage and what does it give you?
• What is server-side rendering (SSR), and why would you use it?
• What is hydration in Angular?

Angular practical coding

• Coding exercise: build a Todo application in Angular.
• Coding exercise: create a search box with debounce in Angular.
• Coding exercise: fetch API data and display it in a table in Angular.
• Coding exercise: implement pagination in Angular.
• Coding exercise: create a login form with validation in Angular.
• Coding exercise: build a parent-child communication example in Angular.
• Coding exercise: implement sorting and filtering in Angular.
• Coding exercise: create a shopping cart in Angular.
• Coding exercise: implement JWT authentication in an Angular app.
• Coding exercise: build a reusable modal component in Angular.
• Coding exercise: implement lazy loading in Angular.
• Coding exercise: create a file upload component in Angular.
• Coding exercise: build an autocomplete dropdown in Angular.
• Coding exercise: implement infinite scrolling in Angular.

Angular routing

• How does routing work in Angular?
• What is the difference between routerLink and href?
• How do you read route parameters and query parameters?
• What is lazy loading, and how do you do it with routes?
• What are route guards? Give examples.
• What is a resolver, and when would you use one?
• How do child routes and nested router outlets work?
• How do you handle 404 pages and redirects?

Angular signals and change detection

• What are signals in Angular?
• What is the difference between signal, computed and effect?
• How do signal inputs, outputs and model() work?
• What is change detection in Angular?
• What is the OnPush change detection strategy?
• What is Zone.js and what does it do?

Angular testing, tooling and architecture

• How do you write a unit test for a component or a service in Angular?
• What is the difference between unit, integration and end-to-end tests?
• How do you test a component that calls an API?
• How do you test route guards, pipes and directives?
• What does ng lint and a formatter give you, and what other tooling do Angular teams use?
• How do you handle environment-specific settings in Angular?

Authentication and security

• How should you store passwords?
• What is a JWT and how is it used for login?
• What is the difference between authentication and authorisation?
• How do you write authentication middleware in Express?
• Where should you store a JWT in the browser?
• What is an ownership check and why is it important?
• What do helmet and rate limiting protect against?
• What is CSRF and when do you need protection?
• What is XSS and how do you prevent it in a MERN app?

Closing the interview

• Do you have any questions for us?

Customer service

• How would you handle an angry customer?

Driving and delivery

• What do you do before starting a delivery route?

Express basics and middleware

• What is Express?
• How do you create a basic Express server?
• What is middleware in Express?
• What is the difference between req.params, req.query and req.body?
• What does express.json() do?
• What is CORS and why do you need it?
• What is the purpose of express.Router?
• What is the difference between app.use and app.get?
• How does error-handling middleware work in Express?
• What is the recommended project structure for an Express API?
• How do you serve static files with Express?
• What changed in Express 5 compared with Express 4?

HR and behavioural

• Tell me about yourself.
• What are your strengths and weaknesses?
• Why do you want to work for our company?
• Where do you see yourself in five years?
• Why should we hire you?
• Tell me about a time you faced a difficult situation at work or study.
• What are your salary expectations?
• Why did you leave your last job (or why is there a gap in your resume)?
• You have no experience. Why should we hire you?

MERN architecture and scaling

• What is the MERN stack and what does each letter do?
• What are the pros and cons of the MERN stack?
• Why is the MERN stack popular for beginners building full-stack projects?
• What is the difference between a monolith and microservices, and what suits a small MERN team?

MERN: connecting React and the API

• How does a React app call an Express API?
• How do you set up a Vite proxy for development?
• How do you serve a React build from Express?
• How do you handle authentication state in a MERN frontend?
• How do you handle loading, error and empty states for API data in React?
• How do you build a dashboard with filters and pagination backed by the API?

MongoDB and Mongoose

• What is MongoDB and how is it different from a SQL database?
• What is Mongoose and why use it?
• How do you connect Express to MongoDB with Mongoose?
• What is a Mongoose schema and model?
• How do you perform CRUD with Mongoose?
• What is the difference between embedding and referencing documents?
• What does populate do in Mongoose?
• What are indexes and why do they matter?
• How does validation work in Mongoose, and is it enough?
• What is the aggregation pipeline?
• What is the difference between find().lean() and a normal Mongoose document?
• How do you prevent NoSQL injection?

Node.js basics

• What is Node.js?
• Is Node.js single-threaded?
• What is npm and what is package.json?
• What is the difference between dependencies and devDependencies?
• What are environment variables and why use them?
• What is the difference between Node.js and the browser JavaScript environment?
• What is the difference between CommonJS and ES modules in Node?
• What is the event loop?

Node.js modules, files and async

• What is a callback, and what is callback hell?
• What is a Promise?
• How do async and await work?
• How do you read a file in Node?
• What does the path module do and why use it?
• What is the difference between Promise.all, allSettled, race and any?
• Why is it a problem to await inside a loop, and what is the alternative?
• What are streams in Node and when do you use them?
• What is an EventEmitter?
• How do you handle unhandled promise rejections?

Node.js testing, performance and deployment

• How do you test a Node API?
• What is pm2 and why use it?
• What is a reverse proxy and why put nginx in front of Node?
• How do you deploy a MERN app to a VPS?
• How do you do graceful shutdown in Node?
• How do you log properly in a production Node app?
• How do you improve the performance of a Node API?
• What is a health check endpoint?

Office and accounts

• How do you prioritise when you have many tasks and short deadlines?
• How do you make sure your work is accurate?

Python advanced features

• What is a generator and what does yield do?
• What is a decorator?
• What is the difference between an iterator and an iterable?
• What are threads, processes and asyncio, and when do you use each?
• How do async and await work in Python?
• What is functools.lru_cache?
• What are the walrus operator and match statement?

Python basics

• What is Python and why is it popular?
• Is Python compiled or interpreted?
• How does Python use indentation?
• What is the difference between a list and a tuple?
• What are Python comments and docstrings?
• What is PEP 8?
• What is the difference between Python 2 and Python 3?
• What is the Python GIL?

Python classes and OOP

• What is a class and an object?
• What is __init__ and what is self?
• What is the difference between instance, class and static methods?
• What is inheritance?
• What is the difference between __str__ and __repr__?
• How does Python do encapsulation, since it has no private keyword?
• What is the @property decorator?
• What are dunder (magic) methods?
• What is polymorphism and duck typing?
• What is the difference between composition and inheritance?

Python control flow and functions

• What is the difference between a for loop and a while loop?
• What do break, continue and pass do?
• How do you define a function, and what are default arguments?
• What is the difference between return and print?
• What are *args and **kwargs?
• Why is a mutable default argument dangerous?
• What is a lambda function?
• Explain scope and the LEGB rule.
• What are list comprehensions?
• What is recursion, and what are its limits in Python?

Python data types and strings

• What are the main built-in data types in Python?
• What is the difference between == and is?
• What does it mean that strings are immutable?
• How do you format strings in Python?
• How do you take input from the user, and what type does it return?
• What are truthy and falsy values?
• What is the difference between shallow copy and deep copy?
• What is the difference between mutable and immutable types, and why does it matter?
• How does Python manage memory?
• What is type hinting and does Python enforce it?

Python data, testing and performance

• How do you test Python code?
• What is pandas and what is a DataFrame?
• How do you read a CSV file and compute a total with Python?
• What is NumPy and why is it faster than lists?
• What is mocking, and how do you do it in Python tests?
• What are pytest fixtures?
• How do you handle missing data in pandas?
• How do you build a small web API in Python?
• How do you automate files and folders with Python?

Python errors and files

• How does try/except work?
• How do you raise an exception and create a custom one?
• How do you read and write a file safely?
• How do you work with JSON and CSV files?
• What is a context manager?
• What does "EAFP" mean?
• How do you log properly in Python?

Python lists, dictionaries and sets

• How do you add and remove items from a list?
• What is a dictionary and how do you use it?
• What is a set and when would you use one?
• How do you remove duplicates from a list while keeping order?
• How do you sort a list of dictionaries by a key?
• What is the time complexity of common list, dict and set operations?
• How do you merge two dictionaries?
• What is defaultdict and Counter?
• What is the difference between a list and a deque?
• What is unpacking and how can you use it?
• How do you iterate with index and with two lists together?

Python modules, packages and environments

• What are modules and packages?
• What is pip and what is requirements.txt?
• What is a virtual environment and why use it?
• What does if __name__ == "__main__" do?
• What is the difference between import styles and circular imports?
• How do you structure a medium-sized Python project?

REST API design and errors

• What is a REST API?
• What is the difference between PUT and PATCH?
• Which HTTP status codes should you know?
• What is the difference between 401 and 403?
• What makes a request idempotent, and which methods are?
• How do you validate input in an Express API?
• How do you implement pagination in an API?
• How should an API return errors?
• How do you version an API?

React 19 and architecture

• What are React Server Components, in simple terms?
• What is the difference between client-side rendering, server-side rendering and static generation?
• What are error boundaries and how do you use them?
• What are portals and when do you use them?
• What is new in React 19 that a developer should know?

React JSX, components and props

• What is JSX?
• What are the rules of JSX?
• What is a component? What is the difference between a function and a class component?
• What are props, and can a component change its own props?
• What is the children prop?
• How do you render a list in React, and why do you need a key?
• What is a fragment and why would you use it?
• What are default props and how do you set default values today?
• What is prop drilling, and how can you avoid it?
• What is the difference between controlled and uncontrolled components?

React basics

• What is React, and why do people use it?
• What is the virtual DOM, and how does React use it?
• What is the difference between a library and a framework? Is React one or the other?
• How do you create a new React project?
• What does ReactDOM.createRoot do?
• What are the main benefits and drawbacks of React?
• What is one-way data flow in React?
• What happens when you call setState (or a state setter) in React?

React data fetching and state libraries

• How do you show loading and error states when fetching data?
• What does TanStack Query (React Query) give you over useEffect and fetch?
• What is the difference between server state and client state?
• When do you need Redux, Zustand or another state library?
• What is Redux Toolkit and why is it recommended over plain Redux?
• What is optimistic UI and how can you build it?

React hooks and effects

• What are hooks, and what are the rules of hooks?
• What does useEffect do?
• What does the dependency array of useEffect mean?
• Why does an effect run twice in development?
• What is the cleanup function in useEffect, and when does it run?
• How do you fetch data in a React component with useEffect?
• What are race conditions in effects and how do you prevent them?
• When should you NOT use useEffect?
• What is the difference between useEffect and useLayoutEffect?
• How does useReducer work?
• What is a stale closure in React, and how do you fix it?

React performance

• Why does a component re-render, and is re-rendering always bad?
• What does React.memo do?
• What is the difference between useMemo and useCallback?
• What is the React Compiler, and does it replace useMemo and useCallback?
• How do you lazy-load components in React?
• How do you render a very long list efficiently?
• Why can inline objects and functions as props hurt memoisation?

React practical coding

• Coding exercise: build a Todo application in React.
• Coding exercise: create a search box with debounce in React.
• Coding exercise: fetch API data and display it in a table in React.
• Coding exercise: implement pagination in React.
• Coding exercise: create a login form with validation in React.
• Coding exercise: build a parent-child communication example in React.
• Coding exercise: implement sorting and filtering in React.
• Coding exercise: create a shopping cart in React.
• Coding exercise: implement JWT authentication in a React app.
• Coding exercise: build a reusable modal component in React.
• Coding exercise: implement lazy loading in React.
• Coding exercise: create a file upload component in React.
• Coding exercise: build an autocomplete dropdown in React.
• Coding exercise: implement infinite scrolling in React.

React refs, context and custom hooks

• What is useRef used for?
• What is Context and when would you use it?
• What is a custom hook?
• What is forwardRef and how does it change in React 19?
• What is the difference between useRef and useState?
• How can Context cause performance problems, and how do you reduce them?
• How do you write a useDebounce hook?
• How do you pass data between sibling components?
• What is useImperativeHandle?

React routing and forms

• What is React Router and what are its basic parts?
• How do you read a URL parameter in React Router?
• What is the difference between Link and an anchor tag?
• How do protected routes work?
• What are nested routes and layout routes?
• Why keep filters and pagination in the URL?
• What is a controlled form in React?
• How do you handle multiple inputs in one form?
• When would you use React Hook Form or a similar library?
• How do you validate a form properly?

React state and events

• What is state, and how is it different from props?
• How does useState work?
• How do you handle events in React?
• Why should you not change state directly?
• What is "lifting state up"?
• Why can a state update seem to use an old value, and how do you fix it?
• What is state batching in React?
• When should you use useReducer instead of useState?

React testing, accessibility and TypeScript

• How do you test a React component?
• Why does Testing Library prefer getByRole over test ids?
• How do you mock API calls in component tests?
• What is accessibility (a11y) in React and what are the basics?
• How do you use TypeScript with React components?

SQL SELECT, filtering and sorting

• How do you select specific columns and filter rows?
• How do you combine conditions in WHERE?
• What does LIKE do, and what are % and _?
• How do you sort and limit results?
• What does DISTINCT do?
• What is an alias?
• What is the difference between WHERE and HAVING?
• How do you paginate results in SQL?
• How do you find the second highest salary?
• What is the difference between CHAR and VARCHAR?
• How does CASE work?

SQL aggregates and GROUP BY

• What are aggregate functions?
• What is the difference between COUNT(*), COUNT(column) and COUNT(DISTINCT column)?
• What does GROUP BY do?
• How do you find duplicate values in a column?
• What does HAVING do?
• How do you count rows per category including categories with zero rows?
• How do you calculate a running total or percentage of total?
• How do you get the top N rows per group?
• What happens with NULL in GROUP BY and in aggregates?
• How do you pivot rows into columns in SQL?

SQL and database basics

• What is SQL?
• What is a relational database?
• What is the difference between DDL, DML, DCL and TCL?
• What is the difference between DELETE, TRUNCATE and DROP?
• What is NULL and how do you test for it?
• What are common SQL data types?
• What is the difference between SQL and MySQL?
• What is the order in which SQL clauses are executed?
• What is normalisation and why is it done?

SQL changing data safely

• How do you insert, update and delete rows?
• How can you make UPDATE and DELETE safer?
• What is the difference between INSERT ... SELECT and INSERT ... VALUES?
• What is an upsert?
• How do you add a column or change a table?
• What are default values and auto-increment/identity columns?
• How do you delete millions of rows safely?

SQL indexes, transactions and performance

• What is an index and why use it?
• What is a transaction?
• What does ACID mean?
• What is the difference between a clustered and a non-clustered index?
• What is a composite index and why does column order matter?
• How do you check how a query runs?
• Why might an index not be used?
• What are transaction isolation levels?
• What is a deadlock and how do you avoid it?
• What is the N+1 query problem?
• What is a view and when would you use one?
• What are stored procedures, functions and triggers?

SQL joins

• What is a join, and what types are there?
• What is the difference between INNER JOIN and LEFT JOIN?
• How do you find rows in one table that have no match in another?
• What is a self join?
• What is a CROSS JOIN?
• Why does a missing join condition create duplicate or huge results?
• What is the difference between putting a condition in ON and in WHERE for a LEFT JOIN?
• How do you join more than two tables?
• What is the difference between EXISTS and IN, and JOIN?

SQL keys and table design

• What is a primary key?
• What is a foreign key?
• What is the difference between a primary key and a unique key?
• What types of relationships exist between tables?
• What are constraints in SQL?
• Natural key or surrogate key: which is better?
• How do you model a many-to-many relationship?
• What does ON DELETE CASCADE do and when is it risky?
• What is a soft delete and what are its trade-offs?
• When might you denormalise?

SQL subqueries, CTEs and set operations

• What is a subquery?
• What is a correlated subquery?
• What is a CTE and why use one?
• What is a recursive CTE and when is it used?
• What is the difference between a CTE, a view and a temporary table?
• What do INTERSECT and EXCEPT do?
• Why is NOT IN dangerous with NULLs?

SQL window functions

• What is a window function and how is it different from GROUP BY?
• What is the difference between ROW_NUMBER, RANK and DENSE_RANK?
• What do PARTITION BY and ORDER BY do inside OVER?
• What do LAG and LEAD do?
• How do you calculate a running total?

Sales

• How do you handle rejection or a customer saying no?

Skilled trades

• Tell me about a job you completed that you are proud of.

Technology

• Explain the difference between a database and a spreadsheet.
• What is the difference between frontend and backend development?

Warehouse and logistics

• What safety precautions do you follow in a warehouse?
• How do you keep stock records accurate?