Next.js Interview Questions

Next.js Basic Interview Questions

1. How Next.js Works?
2. What are API Routes?
3. What do you mean by SSR?
4. What do you mean by SSG?
5. What do you mean by ISG?
6. How does Next.js handle client-side navigation?
7. Explain the concept of dynamic routing in Next.js:
8. What is meant by Styled JSX in Next.js?.
9. Difference between the pre-rendering types available in Next.js.
10. What is client-side rendering, and how does it differ from server-side rendering?
11. How do you pass data between pages in a Next.js application?
12. What is the difference between Next.js and React JS?
13. What is the purpose of the public folder in Next.js? How do you serve static files like images, fonts, and icons?
14. How do you add meta tags and titles to pages in Next.js using the Head component? Why is this important for SEO?
15. What is Hot Module Replacement (HMR) in Next.js, and how does it improve the development experience?
16. What is the difference between layouts and templates in Next.js App Router?
17. How do you deploy a Next.js application?

Next.js Interview Questions - Intermediate

18. What is the difference between getServerSideProps & getStaticProps functions in Next.js?
19. What is the purpose of the getStaticPaths function in Next.js?
20. What is the purpose of the useEffect hook in React, and how does it relate to Next.js?
21. What do you understand by code splitting in Next.js?
22. How do you handle data fetching in Next.js?
23. What are the different options for styling Next.js apps?
24. How do you work with custom server middleware in Next.js?
25. Explain the purpose of the _app.js file in Next JS.
26. How would you implement server-side rendering (SSR) for a Next JS page?
27. Explain the concept of “Serverless” deployment in the context of Next JS. How does it work, and what are the advantages?
28. What are some best practices for debugging and testing Next JS applications?
29. Why use Create Next App?
30. What is Image Component and Image Optimization in Next.js?
31. What is Environment Variables in Next.js?
32. What is Docker Image in Next.js?

Next.js Intermediate Interview Questions

33. How can you fetch data in Next.js and when to use each method?
34. Explain the concept of “prefetching” in Next.js and how it impacts performance.
35. Can you explain how to internationalize a Next.js application to support multiple languages?
36. How can you handle cross-origin requests (CORS) in a Next.js application when making API requests to a different domain?
37. What is serverless architecture, and how does it relate to Next.js?
38. How do you optimize the performance of a Next.js application?
39. Explain the purpose of the getServerSideProps function.
40. What is the purpose of the next.config.js excludes property?
41. Explain the purpose of the next.config.js headers property.
42. What is the purpose of the next.config.js experimental property?
43. How would you optimize the performance of a large-scale Next.js application?
44. What is the difference between redirects and rewrites in Next.js, and when would you use each?
45. How can you achieve dynamic route-based code splitting without using getServerSideProps in Next.js?
46. Describe scenarios where you would choose to use getStaticProps over getServerSideProps, and vice versa.
47. Explain the purpose of the next export command. When would you use it, and what are its limitations?
48. How can you implement authentication in Next.js? Compare JWT, NextAuth, and Firebase approaches.
49. What is the significance of the _error.js and 404.js files in the pages directory, and how can they be customized for error handling in Next.js?
50. How can you implement conditional redirects in Next.js based on certain criteria, such as user authentication status or role?
51. Explain the purpose of the publicRuntimeConfig and serverRuntimeConfig options in Next.js. How do they differ from regular environment variables?
52. How can you implement custom error boundaries in a Next.js project to gracefully handle errors and prevent the entire application from crashing?

Answers:

1. How Next.js Works?
   Next.js is a React framework that enables server-side rendering and static site generation for React applications. It uses a file-based routing system, where each file in the “pages” directory corresponds to a route in the application. Next.js pre-renders pages at build time (SSG) or on each request (SSR) to improve performance and SEO.
2. What are API Routes?
   API Routes in Next.js allow you to create serverless functions that can handle HTTP requests. They are defined in the “pages/api” directory and can be used to build backend functionality, such as handling form submissions, authentication, or interacting with databases.
3. What do you mean by SSR?
   SSR stands for Server-Side Rendering. It is a technique where the server generates the HTML for a web page on each request, rather than relying on the client-side JavaScript to render the content. This improves performance and SEO, as search engines can easily crawl the pre-rendered HTML.
4. What do you mean by SSG?
   SSG stands for Static Site Generation. It is a technique where the HTML for web pages is generated at build time, rather than on each request. This results in faster load times and improved performance, as the pre-rendered pages can be served directly from a CDN.
5. What do you mean by ISG?
   ISG stands for Incremental Static Generation. It is a feature in Next.js that allows you to update static pages after the initial build. With ISG, you can specify a revalidation time for each page, allowing Next.js to regenerate the page in the background when a request comes in after the specified time has passed.
6. How does Next.js handle client-side navigation?
   Next.js uses the Link component from the ‘next/link’ module to handle client-side navigation. When a user clicks on a Link, Next.js intercepts the click event and performs a client-side transition to the new page without a full page reload, resulting in a faster and smoother user experience.
7. Explain the concept of dynamic routing in Next.js:
   Dynamic routing in Next.js allows you to create routes that can accept parameters. This is done by using square brackets in the file names within the “pages” directory. For example, a file named [id].js would create a dynamic route that can handle different values for “id”, such as /posts/1 or /posts/2.
8. What is meant by Styled JSX in Next.js?.
   Styled JSX is a CSS-in-JS solution that comes built-in with Next.js. It allows you to write scoped CSS styles directly within your React components using the <style jsx> tag. This ensures that the styles are only applied to the specific component, preventing style conflicts.
9. Difference between the pre-rendering types available in Next.js.
   Next.js offers two main types of pre-rendering: Static Site Generation (SSG) and Server-Side Rendering (SSR). SSG generates HTML at build time, while SSR generates HTML on each request. SSG is ideal for pages that don’t change frequently, while SSR is better for pages that require up-to-date data on each request.
10. What is client-side rendering, and how does it differ from server-side rendering?
    Client-side rendering (CSR) is a technique where the browser downloads a minimal HTML page and uses JavaScript to render the content on the client side. In contrast, server-side rendering (SSR) generates the HTML on the server and sends it to the client. SSR improves performance and SEO, while CSR allows for more dynamic and interactive user experiences.
11. How do you pass data between pages in a Next.js application?
    In Next.js, you can pass data between pages using query parameters in the URL, or by using a global state management solution like Redux or Context API. You can also use getServerSideProps or getStaticProps to fetch data and pass it as props to the page components.
12. What is the difference between Next.js and React JS?
    React JS is a JavaScript library for building user interfaces, while Next.js is a framework built on top of React that provides additional features like server-side rendering, static site generation, and a file-based routing system. Next.js simplifies the development of React applications by handling many configuration and optimization tasks out of the box.
13. What is the purpose of the public folder in Next.js? How do you serve static files like images, fonts, and icons?
    The public folder in Next.js is used to store static assets like images, fonts, and icons that need to be served directly to the client. Files in the public folder can be accessed using a relative URL path, starting with a forward slash (/). For example, an image stored at public/images/logo.png can be accessed at /images/logo.png.
14. How do you add meta tags and titles to pages in Next.js using the Head component? Why is this important for SEO?
    In Next.js, you can add meta tags and titles to pages using the Head component from the ‘next/head’ module. You can include the Head component in your page components and add meta tags, titles, and other head elements within it. This is important for SEO because search engines use meta tags to understand the content of your pages and improve their ranking in search results.
15. What is Hot Module Replacement (HMR) in Next.js, and how does it improve the development experience?
    Hot Module Replacement (HMR) is a feature in Next.js that allows developers to see changes in their code immediately without needing to refresh the entire page. HMR updates only the changed modules, preserving the application state and providing a faster feedback loop during development.
16. What is the difference between layouts and templates in Next.js App Router?
    In Next.js App Router, layouts are used to define a common structure for multiple pages, while templates are used to define the structure for a specific page or set of pages. Layouts can include shared components like headers and footers, while templates focus on the unique content of a page.
17. How do you deploy a Next.js application?
    You can deploy a Next.js application using various platforms such as Vercel (the creators of Next.js), Netlify, or traditional hosting services. The deployment process typically involves building the application using the next build command and then uploading the generated files to the hosting platform. Vercel offers seamless integration with Next.js, allowing for easy deployment and automatic optimizations.

Next.js Interview Questions - Intermediate

18. What is the difference between getServerSideProps & getStaticProps functions in Next.js?
    getServerSideProps is used for server-side rendering and fetches data on each request, while getStaticProps is used for static site generation and fetches data at build time.
19. What is the purpose of the getStaticPaths function in Next.js?
    getStaticPaths is used in conjunction with getStaticProps to generate dynamic routes at build time by specifying which paths should be pre-rendered.
20. What is the purpose of the useEffect hook in React, and how does it relate to Next.js?
    The useEffect hook is used to handle side effects in React functional components. In Next.js, it can be used for client-side data fetching, subscriptions, or manipulating the DOM after the component has rendered.
21. What do you understand by code splitting in Next.js?
    Code splitting in Next.js is the process of breaking down the application into smaller chunks that can be loaded on demand. This improves performance by reducing the initial load time and allowing users to download only the necessary code for the current page.
22. How do you handle data fetching in Next.js?
    Data fetching in Next.js can be handled using getStaticProps, getServerSideProps, or client-side data fetching with the useEffect hook.
23. What are the different options for styling Next.js apps?
    Next.js supports various styling options, including CSS Modules, Styled JSX, global CSS, Tailwind CSS, and CSS-in-JS libraries like styled-components and Emotion.
24. How do you work with custom server middleware in Next.js?
    You can create custom server middleware in Next.js by using the next.config.js file to define custom server logic or by creating a custom server using Node.js and Express.
25. Explain the purpose of the _app.js file in Next JS.
    The _app.js file in Next.js is used to customize the default App component that wraps all pages. It allows you to add global styles, layout components, and manage state across the entire application.
26. How would you implement server-side rendering (SSR) for a Next JS page?
    To implement SSR in a Next.js page, you can use the getServerSideProps function to fetch data on each request and pass it as props to the page component.
27. Explain the concept of “Serverless” deployment in the context of Next JS. How does it work, and what are the advantages?
    Serverless deployment in Next.js involves deploying the application to a platform that automatically manages server infrastructure, such as Vercel or AWS Lambda. This allows developers to focus on writing code without worrying about server management. Advantages include automatic scaling, reduced operational overhead, and cost efficiency, as you only pay for the resources you use.
28. What are some best practices for debugging and testing Next JS applications?
    Best practices for debugging and testing Next.js applications include using React Developer Tools, console logging, writing unit tests with Jest and React Testing Library, and using end-to-end testing tools like Cypress.
29. Why use Create Next App?
    Create Next App is a command-line tool that sets up a new Next.js project with a pre-configured development environment, allowing developers to quickly start building applications without worrying about initial setup and configuration.
30. What is Image Component and Image Optimization in Next.js?
    The Image component in Next.js is a built-in component that provides automatic image optimization, including resizing, lazy loading, and serving images in modern formats like WebP. This improves performance and user experience.
31. What is Environment Variables in Next.js?
    Environment variables in Next.js are used to store configuration values that can vary between different environments (development, production). They can be defined in .env files and accessed in the application using process.env.
32. What is Docker Image in Next.js?
    A Docker image for a Next.js application is a lightweight, standalone, and executable package that includes everything needed to run the application, including the code, runtime, libraries, and dependencies. It allows for consistent deployment across different environments.

Next.js Intermediate Interview Questions

33. How can you fetch data in Next.js and when to use each method?
    Data can be fetched in Next.js using getStaticProps for static generation, getServerSideProps for server-side rendering, and client-side fetching with useEffect. Use getStaticProps for content that doesn’t change often, getServerSideProps for dynamic content, and client-side fetching for user-specific data.
34. Explain the concept of “prefetching” in Next.js and how it impacts performance.
    Prefetching in Next.js is the process of loading page resources in the background before the user navigates to that page. This improves performance by reducing load times when the user clicks on a link, resulting in a smoother navigation experience.
35. Can you explain how to internationalize a Next.js application to support multiple languages?
    To internationalize a Next.js application, you can use libraries like next-i18next or react-intl. These libraries provide tools for managing translations, locale detection, and rendering content in different languages based on user preferences.
36. How can you handle cross-origin requests (CORS) in a Next.js application when making API requests to a different domain?
    To handle CORS in a Next.js application, you can configure the server to include appropriate CORS headers in the API responses. If using API routes, you can set headers like Access-Control-Allow-Origin to allow requests from specific domains.
37. What is serverless architecture, and how does it relate to Next.js?
    Serverless architecture is a cloud computing model where the cloud provider manages the server infrastructure, allowing developers to focus on writing code. Next.js can be deployed in a serverless environment, enabling automatic scaling and reduced operational overhead.
38. How do you optimize the performance of a Next.js application?
    Performance optimization in Next.js can be achieved through techniques such as code splitting, lazy loading, image optimization, using static generation (SSG), minimizing JavaScript bundle size, and leveraging caching strategies.
39. Explain the purpose of the getServerSideProps function.
    The getServerSideProps function is used to fetch data on each request for a Next.js page, enabling server-side rendering. It allows you to pass dynamic data as props to the page component.
40. What is the purpose of the next.config.js excludes property?
    The excludes property in next.config.js is used to specify files or directories that should be excluded from the build process, helping to reduce the bundle size and improve performance.
41. Explain the purpose of the next.config.js headers property.
    The headers property in next.config.js allows you to define custom HTTP headers for specific routes in your Next.js application, enhancing security and performance.
42. What is the purpose of the next.config.js experimental property?
    The experimental property in next.config.js is used to enable experimental features in Next.js that are not yet stable, allowing developers to test and provide feedback on new functionalities.
43. How would you optimize the performance of a large-scale Next.js application?
    To optimize a large-scale Next.js application, you can implement techniques such as code splitting, lazy loading, server-side rendering, static site generation, image optimization, caching strategies, and monitoring performance metrics to identify bottlenecks.
44. What is the difference between redirects and rewrites in Next.js, and when would you use each?
    Redirects in Next.js are used to send users from one URL to another, changing the URL in the browser. Rewrites, on the other hand, allow you to map one URL to another without changing the URL in the browser. Use redirects for permanent or temporary URL changes, and rewrites for URL masking or proxying requests.
45. How can you achieve dynamic route-based code splitting without using getServerSideProps in Next.js?
    You can achieve dynamic route-based code splitting in Next.js by using dynamic imports with the next/dynamic module. This allows you to load components on demand based on the route, reducing the initial bundle size.
46. Describe scenarios where you would choose to use getStaticProps over getServerSideProps, and vice versa.
    Use getStaticProps when the data for a page does not change frequently, such as blog posts or documentation, to take advantage of static site generation. Use getServerSideProps when the data needs to be up-to-date on each request, such as user-specific dashboards or real-time data.
47. Explain the purpose of the next export command. When would you use it, and what are its limitations?
    The next export command is used to generate a static version of a Next.js application that can be deployed to any static hosting service. It is useful for sites that do not require server-side rendering or dynamic functionality. Limitations include the inability to use server-side features like API routes or getServerSideProps.
48. How can you implement authentication in Next.js? Compare JWT, NextAuth, and Firebase approaches.
    Authentication in Next.js can be implemented using JWT (JSON Web Tokens) for stateless authentication, NextAuth for a complete authentication solution with built-in providers, or Firebase for a backend-as-a-service approach. JWT provides flexibility but requires more setup, NextAuth simplifies the process with pre-built features, and Firebase offers a scalable solution with real-time database integration.
49. What is the significance of the _error.js and 404.js files in the pages directory, and how can they be customized for error handling in Next.js?
    The _error.js file is used to handle server-side errors, while the 404.js file is used to display a custom page for not found errors. They can be customized by creating these files in the “pages” directory and defining custom error messages and layouts.
50. How can you implement conditional redirects in Next.js based on certain criteria, such as user authentication status or role?
    Conditional redirects in Next.js can be implemented using the getServerSideProps function to check the user’s authentication status or role and return a redirect object if the conditions are met.
51. Explain the purpose of the publicRuntimeConfig and serverRuntimeConfig options in Next.js. How do they differ from regular environment variables?
    publicRuntimeConfig and serverRuntimeConfig in Next.js are used to define configuration values that can be accessed at runtime. publicRuntimeConfig is accessible on both the client and server, while serverRuntimeConfig is only accessible on the server. They differ from regular environment variables, which are typically defined at build time and cannot be changed at runtime.
52. How can you implement custom error boundaries in a Next.js project to gracefully handle errors and prevent the entire application from crashing?
    Custom error boundaries in a Next.js project can be implemented by creating a React component that uses the componentDidCatch lifecycle method to catch errors in its child components. You can then wrap your page components with this error boundary component to handle errors gracefully and display a fallback UI instead of crashing the entire application.