15 Most Common NextJS Interview Questions (With Example Answers)

Technical Questions

What is Next.js and how does it differ from React?

React is mainly a frontend library for building components and managing UI states. However, it doesn’t handle things like routing, server-side rendering, or SEO. Next.js basically fills in those gaps. It’s a comprehensive framework built on top of React that handles routing automatically, supports both client-side and server-side rendering, and even allows you to create API routes. React is like a foundation, and Next.js is what helps you take that foundation into production.

What is dynamic routing in Next.js, and how do you implement it?

Dynamic routing lets you build pages based on variable data. Essentially, you create the file with brackets, and Next.js automatically maps it to your data. You can use getStaticPaths to pre-build pages for known routes.

I used this when building a small e-commerce site for my university’s entrepreneurship club. Each product had its own page, but the database updated frequently as we added new inventory. Using dynamic routes with getServerSideProps made it easy to display new products instantly, while older ones were still accessible. It was my first real exposure to the power of file-based routing when your app scales up.

What are API routes in Next.js and when are they useful?

API routes let you create backend endpoints directly inside your Next.js app without requiring a separate server. You just put them inside “/pages/api”, and each file becomes an endpoint automatically.

During my internship last summer, I worked on an internal dashboard that allowed users to submit feedback on our product demos. Instead of spinning up a new Express backend, I built an API route that accepted POST requests and saved responses to a Supabase table. It reduced deployment complexity and ensured that the frontend and backend were all in one codebase.

What is static site generation (SSG) in Next.js and how does it compare to SSR?

Static Site Generation (SSG) means the page is built once during deployment and then served as HTML. This makes it extremely fast and helpful for SEO. Server-Side Rendering (SSR), on the other hand, generates the HTML on every request, which keeps data fresh but adds latency. SSG prioritizes speed, while SSR prioritizes freshness; choosing between them depends on which matters more for that page. I’d use SSG for something like a company blog or documentation, and SSR for something that changes frequently, such as a pricing page with live data.

How do getStaticProps and getServerSideProps differ? When would you use each?

GetStaticProps runs at build time, making it particularly helpful for pages that don’t need to update frequently. GetServerSideProps runs every time someone visits the page, which ensures the data is always up to date. In the past, I used getStaticProps when building a resource site for my computer science club. The content (articles, tutorials) didn’t change often, so pre-rendering made the site super fast. But for the dashboard where users uploaded new projects, I used getServerSideProps so that the page always displayed the latest submissions without requiring a rebuild each time.

Example Analysis

This is a concise and technically accurate answer where you clearly explain the key difference between getStaticProps and getServerSideProps while grounding it in a real example. It shows you understand not just what they do, but when to use them. To make it top 1%, I’d add one line on trade-offs. For instance, mentioning getStaticProps’s faster performance vs. getServerSideProps’s higher server load.

Explain how getStaticPaths works.

Middleware runs before a request is completed, which makes it useful for authentication, redirects, or localization. Middleware is like a lightweight filter that runs at the edge, close to the user. When I was working on a team project for a startup accelerator, we developed a mentorship platform that offered users varying access levels. I wrote middleware that checked if a user’s JWT was valid and matched their role before allowing access to mentor-only dashboards. Because it ran at the edge, it added almost no latency, and we didn’t need to load extra auth logic on the client.

What is Incremental Static Regeneration (ISR)?

ISR combines the speed of SSG with the freshness of SSR. It pre-renders pages, but also tells Next.js to re-generate them in the background after a set time. In an e-commerce project I helped with, we had thousands of products but didn’t want to rebuild the entire site every time inventory changed. We used ISR with a 10-minute revalidation interval. That way, users saw lightning-fast static pages, and updated inventory appeared automatically within minutes, without the need for constant manual deploys.

How do you optimize performance in a Next.js application?

I always start by making sure I’m using the right rendering method, SSG or ISR, whenever possible. Then I focus on lazy-loading components, using dynamic imports to split code, and optimizing images. When I was working on a portfolio site for a class project, I ran performance audits with Lighthouse and found that my landing page’s image was tanking the load time. Switching to a responsive image with lazy loading and compressing assets reduced my loading time by nearly half. Small details like that really add up in the production of an in-depth website.

How does image optimization work in Next.js?

Next.js automatically optimizes images using its <Image> component. It serves them in the right size for each device, converts them to modern formats, and lazy-loads by default. You don’t need to manually resize or compress anything when you use the right component. When I replaced all standard <img> tags with <Image> on a client project, our load time dropped noticeably, and the Lighthouse score jumped from 75 to 95.

How do you handle environment variables in Next.js?

Next.js makes handling environment variables pretty clean. You can define them in .env.local, .env.development, or .env.production files to keep everything safe on the server side.

When I was working on a weather app that used the OpenWeather API, I had to store both a public API key for fetching weather data and a private analytics key for server logging. I accidentally exposed the analytics key during early testing, which taught me to always check what’s prefixed before deploying. Since then, I’ve made it a rule to clearly separate client and server variables.

How do you handle error boundaries or fallback UI in Next.js pages?

Error handling in Next.js is structured at two levels: component-level and route-level. For component-level issues, React error boundaries are the best approach as they catch render-time errors and display a fallback UI. At the route or application level, Next.js provides built-in files for custom error and 404 (not found) pages. This layered approach ensures that you can handle both unexpected runtime errors and predictable UI states, such as “not found” or “loading,” gracefully.

What is middleware or edge runtime in Next.js?

Middleware in Next.js allows you to intercept and modify requests before they reach your routes. It runs on the edge runtime, which executes code on CDN edge servers, resulting in extremely low latency. Middleware is commonly used for authentication, redirects, or localization logic. For example, you can restrict access to certain pages by checking a session token or redirect users based on their location, all before any page loads. The edge runtime itself is optimized for speed and scalability. Because it’s stateless and lightweight, edge middleware is ideal for high-traffic apps that need real-time personalization.

Discuss security concerns (e.g. XSS, CSRF) when using Next.js.

Security in Next.js centers on controlling what data is trusted and how it’s rendered. To prevent cross-site scripting (XSS), developers should sanitize all user input and avoid SetInnerHTML unless necessary. For cross-site request forgery (CSRF), adding anti-CSRF tokens or validating the Origin and Referer headers helps ensure requests come from legitimate sources. Next.js also supports custom HTTP headers, so you can enforce policies like Content-Security-Policy and Strict-Transport-Security to mitigate injection attacks. Lastly, use secure cookies with HttpOnly and SameSite flags, and validate all API routes to ensure they only accept expected inputs and methods.

Explain the difference between Server-Side Rendering (SSR), Static Site Generation (SSG), and Incremental Static Regeneration (ISR) in Next.js. When would you use each?

Server-Side Rendering (SSR) generates HTML at request time, ensuring every page load contains the most current data, which is ideal for dashboards or user-specific content. Static Site Generation (SSG) creates pages once at build time, serving them instantly from the CDN. It’s helpful for content that doesn’t change often. Incremental Static Regeneration (ISR) combines both approaches: pages are generated statically but can be revalidated at set intervals, keeping them nearly as fast as SSG while staying up to date. In practice, you might use SSR for authenticated pages, SSG for static content like blogs, and ISR for something in between. Together, these rendering modes give you fine-grained control over performance, cost, and freshness.

Top Next.Js Interview Coaches

Greyson G.

Experience: Former software engineer at Snapchat and Apple, Greyson has built complex front-end systems and performance-sensitive features.

Specialties:

• Technical interview prep
• Mock interviews for software roles
• Guidance on architecture and frontend practices

Greyson is ideal for candidates wanting Next.js + front-end technical prep, since his background includes building front-end systems at scale.

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Justin H.

Experience: Software engineer turned coach on Leland, Justin has a passion for systems thinking and helping candidates break into technical roles.

Specialties:

• Mastering technical interviews (algorithms, front-end, full-stack)
• Coaching on code structure, performance, and scalable architecture
• Guiding you through best practices in web app development

Justin is helpful for those preparing for Next.js interviews, because he can help you sharpen the underlying technical skills that Next.js interviews tests.

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Jake E.

Experience: Full-stack developer at Leland and has experience working with React, Node, and other modern web techs.

Specialties:

• Web development interview prep (React, APIs, full-stack)
• Helping candidates build strong front-end portfolios + projects
• Mock interviews and hands-on coding in web stacks

Jake is a good match for Next.js roles because he works in React and can guide you in both frontend and backend interview parts.

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How to Prep for Your Next.Js Interview

Preparing for a Next.js interview requires more than just knowing the syntax; it’s about demonstrating engineering judgment under pressure. You should be fluent in React fundamentals and able to explain concepts like SSR vs. SSG, ISR, and middleware with clarity and purpose. The best candidates connect these skills to real-world performance, scalability, and user experience. Practice building small apps end-to-end and explain each design choice as if you were reviewing production code. At the top level, everyone can code, but what sets you apart is proving you can think like an engineer who ships.

Next.Js Interview Prep Resources

1. Software Engineering Specializations & Which One is Right for You
2. How Entry Level Software Engineers Can Embrace Responsible Technology in the Digital Age
3. New Grad Software Engineer's Guide to Making Their Mark in a Competitive Industry

Next.Js Interview FAQs

Are Next.Js interviews tough?

• Yes, Next.js interviews are challenging, and that’s by design. Companies that hire for Next.js roles want to see if you can think clearly about architecture and performance under pressure. You’ll face a blend of technical coding questions, system design prompts, and behavioral questions about problem-solving. What makes these interviews tough isn’t just the technical content, but the expectation that you can explain complex topics like SSR vs. SSG in plain, confident language. Interviewers are testing both your depth of understanding and your ability to reason like a production engineer.

How to pass interviews for Next.Js roles?

• To excel in a Next.js interview, start by mastering the fundamentals. Be ready to walk through real-world examples of building scalable apps: when you’d use SSR versus ISR, and how you’d handle API routes securely. Equally important is communication. Next.js interviews reward engineers who can articulate why they made certain design choices, not just how they built something. Practice mock interviews where you explain your reasoning step-by-step while coding. Finally, polish your behavioral answers, as teams want engineers who can collaborate effectively under tight deadlines and think like problem solvers. The strongest candidates combine fluency in tech with structured thinking that shows they’re ready to build and own production systems.