Top 20 Full Stack Interview Questions and Answers for 2025: Master Frontend and Backend Concepts

Megana Natarajan

An extensive range of skills in front-end, backend, database, architecture, deployment, and soft skills is an absolute necessity for full-stack development positions. Recruiters will examine your conceptual knowledge as well as your practical application of that knowledge. 20 of the most commonly asked full-stack interview questions are listed below, with each one being followed by:

Suggested Approach: How you should format your response.
Sample Answer: An example answer that you can change to fit your own scenario.

Use this as a starting point for your learning journey and, if you can, add your own projects, technologies, trade-offs, and results.

Full Stack Developer Interview Questions

What is Full-stack Development?

Suggested Approach: Give a brief definition of the term, list the layers that are involved front-end, back-end, database, and deployment, and then talk about a specific example that highlights the general duties of a full-stack developer.

Sample Answer: Developing an application’s client-side (front-end) and server-side (back-end) layers, including the database, server infrastructure, and deployment pipeline, is called full-stack development. A full stack developer should be at ease working on all elements of the “stack.” This includes creating UI elements, GraphQL or REST APIs, database schema definition, third-party integration, and cloud deployment. Developing a React front-end page, connecting it to an Express/Node API, storing data in a PostgreSQL database, and deploying the service via Docker on AWS. This allows us to take ownership of end-to-end delivery.

What’s the difference between client-side and server-side programming?

Suggested Approach: Compare duties and technology.

Sample Answer: The server-side code executes on a server and processes data, controls authentication, and communicates with databases (Node.js, Python, Java, etc.), whereas client-side code operates in the browser and manages UI/UX (HTML, CSS, JavaScript). Both must be efficiently coordinated by full-stack developers.

What are the advantages/disadvantages of using a relational database vs. a non-relational (NoSQL) database?

Suggested Approach: Compare relational (SQL) and noSQL based on factors such as schema, transactions, scaling, and use cases. Then, proceed to explain when you would choose one over the other.

Sample Answer: Structured schemas, robust ACID transactions, and consistent data integrity are all features of relational databases (such as MySQL and PostgreSQL). Applications where data integrity is critical and there are complex relationships are a good fit for them. On the flip side, they might scale vertically as compared to horizontally and have reduced flexibility. This is because changing the scheme can be expensive. Non-relational (NoSQL) databases, like MongoDB and Cassandra, offer schema flexibility and facilitate horizontal scaling. They work well with large amounts of unstructured or semi-structured data, such as logs or user-generated content. However, they might overlook relational querying or strict transactions. In contrast, one could use a NoSQL database when handling large amounts of user-session data or a document-based store with variable attributes. Also, one could use a relational database when building a financial or order processing system where data consistency is vital.

Can you explain what RESTful APIs are & how they differ from, say, GraphQL?

Suggested Approach: Explain REST, highlight its features, and then compare and contrast GraphQL’s flexibility, over-/under-fetching, versioning, and tooling.

Sample Answer: REST (Representational State Transfer) is an architectural style for networked applications that usually returns JSON/XML responses and works on resources detected by URIs using HTTP methods (GET, POST, PUT, DELETE, and PATCH). Its features include statelessness, a consistent interface, and resource-based URIs. In comparison, GraphQL is a query language for APIs and a runtime for answering these questions. It supports a strongly-typed schema and lets clients specify exactly which fields are needed. This eliminates over- or under-fetching.

Key differences: GraphQL can combine multiple data sources into a single endpoint and evolve without version bumping by adding optional fields. REST often needs multiple endpoints (or suffers from over-fetching), making versioning challenging. However, GraphQL may lead to more complicated tooling overhead, query complexity, and caching. If the data requirements are predictable and standard, it would be ideal to use REST in a full-stack role. If the clients need dynamic, flexible queries or if we are combining data from multiple services, we should use GraphQL.

What is the difference between synchronous and asynchronous programming in JavaScript, and why is it relevant for full-stack development?

Suggested Approach: Discuss promises, callbacks, async-await, and the event-loop. Explain asynchronous and synchronous. Next, connect it to full-stack, for example, managing I/O, reducing blocking, and using Node.js async APIs.

Sample Answer: An example of synchronous programming is when code runs sequentially, with each operation having to finish before the next can be initiated. This program can execute other tasks until the operations (especially I/O, such as database calls or HTTP requests) return due to asynchronous programming. Asynchronous callbacks are handled by JavaScript’s event loop. Promises and async/await are features of more recent syntax that make it easier to manage async flows. Asynchronous programming is vital for full-stack development because you want to prevent the user interface from being blocked while you wait for network calls on the front end and handle a range of I/O operations on the back end (like Node/Express) without leading to thread blocking. Developers run the risk of a slow user interface or a server that scales poorly if one doesn’t understand async.

What is CORS (Cross-Origin Resource Sharing)? How do you handle it in a web application?

Suggested Approach: Describe CORS, explain why browsers implement it, and then demonstrate how to use proxies or front-end/back-end code to allow and manage CORS in a full-stack application.

Sample Answer: Cross-Origin Resource Sharing, also called CORS. Browsers have a security functionality that prevents JavaScript from sending requests to a different origin (domain, port, or protocol). This is unless the target server specifically allows it through HTTP response headers (like Access-Control-Allow-Origin). If your API is hosted at https://api.example.com and your front-end is hosted at https://app.example.com, the browser will block your requests if you don’t include the correct CORS headers. You can configure your server (for instance, in Express, use the cors middleware) to send Access-Control-Allow-Origin: https://app.example.com or *(less secure) and include other needed headers like Access-Control-Allow-Methods and Access-Control-Allow-Headers in order to handle it in a full-stack application. As a replacement, you could deploy the front-end and API under the same origin or use a reverse proxy (like Nginx) to completely avoid CORS.

Name some common web vulnerabilities and how to prevent them.

Suggested Approach: Highlight the main risks and countermeasures.

Sample Answer:

SQL Injection: Use prepared statements/ORMs.
XSS: Sanitize inputs, escape outputs, use CSP.
CSRF: Add CSRF tokens, use SameSite cookies.
Broken Auth: Hash passwords (bcrypt), validate tokens.
HTTPS: Always secure data in transit.

Client and server secure coding is mandatory.

Describe the MVC pattern and how you would implement it in a full-stack application.

Suggested Approach: Describe each part of MVC (Model-View-Controller) and its interactions. Next, describe how you would apply the pattern and map these layers in a typical stack (for example, React + Express + Sequelize)

Sample Answer: Model-View-Controller is called MVC.

Model: Depicts business logic and data (e.g., database schemas, ORM models).
View: The user interface or output that is shown to users (such as server-rendered templates or React components).
Controller: Manages user input, interacts with the model, and outputs data or a view.

When utilizing a full-stack application: On the back-end (such as Node/Express + Sequelize), the Controller includes Express routes and functions that process HTTP requests, retrieve and update the Model, and reply. The Model is a Sequelize model. In a SPA scenario, the back-end may function as an API, and the View layer is fully front-end. Or, the View layer may be a server-rendered template (like EJS). You could decode a variation on the front-end (React): Components (View) manage events (Controller) and link to a state store (Model). The pattern helps in organizing code for testability, maintainability, and separation of concerns.

How do you deploy a full-stack app?

Suggested Approach: Describe the complete procedure.

Sample Answer: Build and test both layers, use Docker to containerize them, push images to a registry, and then use AWS ECS, Heroku, or Vercel for deployment. Configure databases (RDS, MongoDB Atlas), environment variables, and CI/CD pipelines. Finally, closely monitor logs and performance.

What’s the difference between monolithic and microservice architectures?

Suggested Approach: Define and compare.

Sample Answer: A monolith is a codebase that includes all the components. It is simple to start but more difficult to scale. Microservices, which are scalable but difficult to administer, divide the system into separate services that communicate with one another through APIs. For smaller applications, leverage monoliths; for larger, dynamic systems, use microservices.

How do you optimize performance in a full-stack application? Mention some front-end and back-end strategies.

Suggested Approach: Divide into back-end (caching, database indexing, load balancing, asynchronous processing) and front-end (coding, splitting, caching, lazy loading, bundle size reduction) strategies. Give clear examples.

Sample Answer: Code-splitting (so users don’t download the entire app at once), lazy-loading elements and images, using a CDN for static assets, and reducing HTTP requests are some ways to optimize the front-end. Some more methods include using browser caching, postponing non-essential scripts, and avoiding large “blocking” libraries.

Back end:

Use caching (in-memory, like Redis or in HTTP cache).
Databases index on fields that are regularly accessed
Asynchronous jobs for lengthy processes (like message queues).
Pagination for big data sets.
Load-balancing across servers.
Use efficient data structures.
Bottleneck monitoring (CPU, memory, I/O).

When combined efficiently, these tactics reduce latency, increase throughput, and improve user experience.

How would you design a paginated API endpoint?

Suggested Approach: Show a simple API pattern.

Sample Answer: Show a simple API pattern.

GET /api/items?page=2&limit=20
Return JSON with data, totalItems, and pageInfo. Add sorting (sortBy, order) and filtering. Always validate inputs to prevent misuse.

What is the difference between stateful and stateless applications, and why does statelessness matter for scalability?

Suggested Approach: Explain state management, differentiate between stateful and stateless, and then correlate this to scalability (load balancing, horizontal scaling).

Sample Answer: A stateful application retains client-specific session or context on the server side (e.g., server keeps in-memory session data for each user). A stateless application includes all needed context (either on the client side, database, or request token) and handles each request independently. Horizontal scaling is made possible by statelessness. This makes load-balancing, fail-over, and containerization easier because any server instance can manage any request because it doesn’t rely on local session data. In order to easily scale out, one should aim for stateless backend services in a full-stack system, which store session state in a shared store like Redis or use JWT’s client side.

How do you handle API versioning?

Suggested Approach: List methods and best practices.

Sample Answer: Common methods:

URI versioning: /api/v1/users
Header versioning: Accept: application/vnd.app.v2+json
Maintain backward compatibility, deprecate gradually, and document changes clearly.

How do you test a full-stack app?

Suggested Approach: Cover testing layers.

Sample Answer:

Unit Tests: Individual functions/components (Jest, Mocha).
Integration Tests: API + database (Supertest).
E2E Tests: Simulate real use (Cypress, Playwright).
Automate all through CI pipelines to guarantee quality before deployment.

Describe your Git workflow for a full-stack project.

Suggested Approach: Explain branch structure.

Sample Answer: Use feature branching or GitFlow:

main (production), develop (staging), feature/* (new features), hotfix/* (urgent fixes).
PRs trigger CI tests before merging. Tag releases for tracking and rollback.

What is CI/CD, and how would you implement it?

Suggested Approach: Summarize the concept and steps.

Sample Answer: Building, testing, and deployment are all automated by CI/CD. For example, GitHub Actions builds Docker images, deploys to staging or production, and runs tests on push. CD reduces manual labor by guaranteeing that every commit that passes tests can go live safely.

How do you implement caching?

Suggested Approach: Describe the caching layers.

Sample Answer:

Browser/CDN: Use headers to cache static files (Cache-Control).
Server: Use Redis/Memcached to cache database queries or responses.
Database: Use materialized views or add indexes.

When data is updated, ensure cache invalidation is done accurately.

How do you manage environment configurations and secrets?

Suggested Approach: Explain safe handling.

Sample Answer: Store environment variables in managed servers such as AWS Secrets Manager or in .env files. Avoid hard-coding
secrets. Keep development, staging, and production configurations separate, and only include non-sensitive data in front-end builds.

Describe a challenge you solved in a full-stack project.

Suggested Approach: Brief STAR example.