2025 80 curated interview questions

80 Full Stack Interview Questions

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1. What tools do you use for testing your code? Why?

I typically use a combination of Jest for my unit tests and Cypress for end-to-end testing. Jest is my go-to for unit tests because it's well-integrated with JavaScript frameworks like React, it's fast, and has a powerful mocking system. For end-to-end testing, I prefer Cypress due to its intuitive interface for simulating user interactions and its ability to take snapshots during test runs, which makes debugging really straightforward. Additionally, I use ESLint and Prettier to ensure code quality and consistency.

2. Can you briefly explain what a Full Stack Developer does on a day-to-day basis?

A Full Stack Developer works on both the front-end and back-end sections of an application or website. On the front-end, they build and design the user interface ensuring seamless functionality and user experience. This often involves working with languages like HTML, CSS and JavaScript. On the back-end, they help to manage the server, database, and any application and data integration that the solution might need. This frequently involves programming languages and platforms like Python, Ruby, PHP or .NET, and databases like MySQL or MongoDB. In general, a Full Stack Developer's role is all about weaving together the entire process of application development, navigating between user interactions and data handling seamlessly.

3. What programming languages and frameworks are you comfortable working in?

While the specific answer can vary for each individual based on their experience, an ideal response could be something like:

In terms of programming languages, I have experience working with JavaScript, Python, and Java. These have been my go-to languages due to their versatility and widespread use. As a Full Stack Developer, I have worked with JavaScript on the front-end along with React.js as a framework to develop user interfaces, and Vue.js for building user-friendly applications.

On the back-end, my experiences mostly lie with the Node.js environment. As for Python, I have used it mainly when dealing with data-focused projects and relied on Django as a framework for web application development. Additionally, I have experience working with relational databases like MySQL and PostgreSQL along with NoSQL databases like MongoDB.

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4. Could you tell me about your most complex project to date? What was your role within the project?

Certainly, the most complex project I've handled to date was developing an online food delivery platform similar to Grubhub or Uber Eats. The complexity of this project was due to its rich feature set that included real-time updates, payment integration, maps integration, complex database relationships, and high-level security.

As a Full Stack Developer, my role was to ensure a seamless integration of both front-end and back-end activities. On the front-end side, I utilized React.js to build a compelling, user-friendly interface and ensured its responsiveness for different screen sizes. Especially challenging was the integration of real-time updates, such as notifying users about their delivery status or new promotional offers, which I achieved using WebSockets.

On the back-end, Node.js server with Express.js framework was used along with a MongoDB database. I built several REST APIs to handle tasks like user registration, authentication, placing an order, and more.

The integration of a third-party payment gateway, like Stripe, was another crucial part of my role. I also orchestrated maps integration which allowed users to see their food being delivered in real-time.

Overall, this project was very demanding but equally rewarding as it really broadened my experience and understanding of full stack development in a practical, real-world setting.

5. Can you explain your experience with front end development? What technologies have you used?

Throughout my career, I have amassed significant experience in front-end development, extensively working with the core trifecta of HTML, CSS and JavaScript. HTML and CSS have been the foundational elements for creating and styling web pages. JavaScript, on the other hand, has offered the dynamism needed for user interaction.

In terms of working with JavaScript frameworks, I have used React.js and Vue.js to create interactive UIs. React in particular has been a mainstay in my projects due to its efficient re-rendering and view component features. I've also gotten quite adept at handling AJAX requests, and working with JSON and XML data formats.

In addition, I have a good knack for creating responsive web designs by using CSS Flexbox and Grid systems to ensure seamless rendering on multiple screen sizes. I have also adopted various preprocessors like SASS for efficient stylesheet management.

6. How do you manage version control in your projects?

I predominantly utilize Git for version control in my projects due to its extensive features and widespread acceptance in the development community. Git allows me to create separate branches for developing specific features without affecting the main code, thereby managing changes in a linear but non-blocking manner.

When a feature is completed and tested, I merge the branch into the main code base, resolving any conflicts that may arise. This also enables me to easily roll back to a previous stable version if a newly implemented feature introduces bugs or breaks functionality.

Additionally, for larger projects where I collaborate with a team, I use platforms like GitHub or Bitbucket. These platforms facilitate easy sharing of codebase among team members, allow reviewing changes made by peers, and support pull request mechanism to manage code merging systematically, helping maintain the overall integrity and stability of the project.

7. How do you test and debug your code?

In my process, testing and debugging are ongoing activities that happen alongside development. While writing code, I follow the practice of writing small chunks of functionality and testing them immediately. This helps in catching any obvious bugs early and ensures that new functionality doesn't break existing features.

For testing, I typically use unit testing frameworks like Jest for JavaScript, or PyTest for Python. These tools allow me to write test cases and automate the task of running these tests. They also provide helpful reporting on the tests that were run, which is very useful for identifying problems.

When it comes to debugging, I typically start by using the built-in debugging tools in the integrated development environment (IDE) or the browser. Breakpoints and console logs are simple yet powerful tools for inspecting running code, understanding program flow, and identifying where things are going wrong. For more complex issues, I might use more advanced tools or techniques like Postman for API testing, or Wireshark for inspecting network traffic. Overall, the key is to have a systematic approach and to use the tools that best fit the situation.

8. Have you ever had to deal with a difficult bug? How did you resolve it?

Absolutely, dealing with tough bugs is a regular part of any developer's job. One particularly challenging bug I encountered was in a web application where randomly, some users were getting logged out for no apparent reason. These bugs, which are intermittent and not easily reproducible, are often the trickiest to address.

To resolve it, I started analyzing the behavioral patterns of the users experiencing issues, trying to identify any commonalities. This didn't yield much, so I turned to our system logs. I started digging into the server logs around the times when logouts happened. The problem turned out to be an issue with our session management where under certain rare conditions, the server was mistaking valid sessions as expired and forcing a logout.

To fix this, I had to tweak our session management logic and include additional checks to correctly validate session expiry. It was a time-consuming process, but a great learning experience. It emphasized the critical role of comprehensive logging and strategic problem analysis in debugging.

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9. Can you tell me about a time you worked with a backend technology?

10. Can you explain REST and why it's useful in web development?

11. How are horizontal scaling and vertical scaling different from each other?

12. What tools do you typically use for profiling and optimizing performance?

13. Can you tell me what functional programming is?

14. Can you explain the differences between a relational database and a non-relational database?

15. What does MVC stand for, and why is it useful?

16. How would you store passwords in a database?

17. Have you worked on any continuous integration or deployment processes?

18. Can you explain the concept of state management in front-end applications?

19. How can you avoid callback hell in Node.js applications?

20. What are the differences between GET and POST HTTP methods?

21. How do you approach troubleshooting server-side issues?

22. Can you tell me about an API you've built from scratch?

23. Can you describe your experience with API design?

24. Can you list some best practices for debugging JavaScript?

25. Can you describe your experience with responsive design?

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