Top 50 Next.js Interview Questions [2024]

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Here are some essential Next.js interview questions for freshers. These questions cover the fundamental concepts of Next.js, helping you build a solid foundation in the framework.

1. What Is Next.js?

Next.js is a React framework designed to create highly optimized, SEO-friendly, and user-centric static websites and web applications. It provides an exceptional developer experience for building production-ready applications, complete with all the necessary features.

2. What Is Next.js Used for?

Next.js is commonly used to create highly performant and SEO-friendly websites, such as:

• E-commerce platforms: For fast-loading, optimized shopping experiences.
• Marketing sites: To enhance SEO and user engagement.
• Landing pages: For quick, responsive, and efficient lead generation.

Additionally, Next.js is often used for building dashboards, blogs, and applications requiring server-side rendering or static site generation. This question often appears in Next.js interview questions.

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3. What Is the Difference Between Next.js and React.js?

Next.js is a framework built on top of React.js, providing additional features like server-side rendering and static site generation, while React.js is a JavaScript library for building UI components.

Understanding this distinction is crucial to remember when preparing for Next.js interview questions, as it highlights the key advantages of Next.js over React.js.

Here's the difference between Next.js and React.js:

4. Is Next.js Back-End, Front-End, or Full-Stack?

Next.js is considered a full-stack framework because it allows both client-side and server-side rendering. This is particularly valuable when working with React, which is primarily focused on front-end development, while Next.js provides additional support for server-side functionality.

This question often appears in Next.js interview questions, and understanding how it supports both front-end and back-end tasks is essential to highlight its full-stack capabilities.

5. What Is the Process of Installing Next.js?

Below are the steps for installing the Next JS:

• Make sure Node.js is installed on your system.
• Open your terminal and create a new Next.js project by running:

For npm:

  
  npx create-next-app@latest

  

For Yarn:

  yarn create next-app

  

• Once the installation is complete, navigate into your project folder:

  cd your-project-name

• Start the development server:

  npm run dev
  # or
  yarn dev

Open your browser and go to http://localhost:3000 to see your new Next.js application.

6. What Are the Features of Next.js?

Next.js offers key features like server-side rendering, static site generation, and API routes, providing flexibility for building dynamic and optimized web applications. Knowing these features is helpful when tackling Next.js interview questions effectively.

Below are some of the features of Next.js:

• Built-in CSS Support: Allows importing CSS files directly and uses styled-jsx for scoped styling.
• File-system Routing: Automatically creates routes based on the page's directory structure, eliminating the need for extra routing libraries.
• Image Optimization: The Next.js image component optimizes images for different devices and viewports, loading them only when they enter the viewport.
• Incremental Static Regeneration (ISR): Combines SSG and SSR, allowing pages to be updated at runtime and cached for faster future responses.
• Fast Refresh: Provides real-time updates to React components for immediate feedback during development.
• SEO Optimization: Manages meta tags and provides a built-in Head component to enhance SEO for each page.
• TypeScript Support: Easily integrates TypeScript into new or existing projects without extra configuration.
• Data Fetching: Supports SSR, SSG, and ISR for various data fetching strategies.
• Lazy Loading: Delays loading resources until needed, improving load times and performance.

7. Why Use Create Next App?

Using Create Next App simplifies the setup process by providing a fully configured Next.js project with minimal effort, allowing developers to focus on building features instead of configurations. This is a crucial topic in Next.js and is often asked during Next.js interview questions.

Below are the reasons why to use the Create Next App:

• Rapid Project Initialization: Sets up a new Next.js application in seconds, enabling quick transition from idea to implementation and boosting productivity.
• User-Friendly Setup Process: Runs npx create-next-app@latest to provide an interactive setup experience, ideal for newcomers and ensuring best practices.
• Zero Dependencies: Operates without external dependencies, resulting in faster installation and fewer conflicts or security issues.
• Offline Functionality: Works without an internet connection by using your local package cache to bootstrap the project.
• Access to Pre-built Examples: Allows starting projects with examples from the Next.js collection, such as projects with API routes.
• Reliability Through Testing: Undergoes Next.js testing to ensure reliability with each release.

8. What Is Next.js Routing?

Next.js routing is a key topic often covered in Next.js interview questions. It uses a file-system-based routing mechanism, where routes are automatically created based on the structure of the pages directory. This approach simplifies navigation by mapping files directly to routes and supports dynamic and nested routing without requiring additional routing libraries.

9. What Are the Types of Routes in Next.js?

This is a frequently asked interview question for React JS positions that involve Next.js. The following are the types of routes in Next.js:

• Static Routes: In Next.js, files in the pages directory with extensions .js, .jsx, .ts, and .tsx are automatically mapped to routes. The index.js file represents the root directory. For example, creating a file named index.js in the pages directory will be accessible at http://localhost:3000/:

// pages/index.js

const Home = () => {
  return (
    <div>
      Home Page
    </div>
  );
}
export default Home;

• Nested Routes: Next.js supports nested routing based on the folder structure within the pages directory. For instance, if you create a folder named users and add a file called about.js inside it, the route will be accessible at http://localhost:3000/users/about:

// pages/users/about.js

const About = () => {
  return (
    <div>
      About Page
    </div>
  );
}
export default About;

• Dynamic Routes: Next.js allows dynamic routing using the bracket syntax. This enables URL parameters in your routes. For example, creating a file [id].js in the pages/users directory will allow the component to access the id parameter and render content accordingly. This route can be accessed at http://localhost:3000/users/<any-dynamic-id>:

// pages/users/[id].js

import { useRouter

 } from 'next/router';

const User = () => {
  const router = useRouter();
  const { id } = router.query;

  return <p>User: {id}</p>;
};

export default User;

• API Routes: Next.js also supports API routes, which can be created by adding files to the pages/api directory. Each file in this directory corresponds to an API endpoint. For example, creating a file hello.js in the pages/api directory will map to the endpoint http://localhost:3000/api/hello:

// pages/api/hello.js

export default function handler(req, res) {
  res.status(200).json({ message: 'Hello, world!' });
}

Understanding these route types will help you answer Next.js interview questions, as they demonstrate the flexibility and power of Next.js routing.

10. What Methods Can You Use to Pass Data Between Pages in Next.js?

This approach to data passing is a common topic in Next.js interview questions, as it highlights an understanding of both Next.js and React state management concepts. In Next.js, you can pass data between pages using several methods:

• Using the Link Component: Use the Link component from Next.js to navigate between pages and pass data through the href prop. The href should be an object with pathname and query properties.
• Set Pathname and Query: Specify the target page's route with pathname and include the data to be transferred in the query object.
• Access Data on Target Page: On the target page, use the useRouter hook from next/router to access the router object.
• Extract Data from Query Object: Extract the data from the query parameters within the target page component using the router object.
• Test Navigation and Data Access: Ensure that navigation works as expected and verify that the data is correctly passed and retrieved on the target page.

Understanding these methods will help you answer Next.js interview questions, as passing data between pages is one of the most frequently asked topics.

11. Explain the Concept of Dynamic Routing in Next.js

Dynamic routing in Next.js allows you to generate routes based on data, which can change over time, providing a scalable and flexible approach to handling content.

For example, consider a news site where article data is stored in a CMS:

[
  {
    "id": 0,
    "slug": "breaking-news",
    "title": "Breaking News",
    "content": "This just in..."
  },
  {
    "id": 1,
    "slug": "latest-updates",
    "title": "Latest Updates",
    "content": "Here's what's happening now..."
  }
]

With dynamic routing, you can automatically generate pages for each article based on its slug. For instance, you would have routes like https://news.example.com/article/breaking-news and https://news.example.com/article/latest-updates without manually creating individual HTML files.

When a new article is added:

[
  ...
  {
    "id": 2,
    "slug": "new-developments",
    "title": "New Developments",
    "content": "Updates on recent events..."
  }
]

Dynamic routing ensures that a new page, https://news.example.com/article/new-developments, is automatically created. This approach simplifies the management of large numbers of pages and is a key concept in Next.js, and it often appears in Next.js interview questions.

12. What Is Meant by Styled JSX in Next.js?

Styled JSX is a CSS-in-JS solution built into Next.js that enables component-level styling. This approach is often featured in Next.js interview questions. It allows you to write CSS directly within your components, ensuring that styles are scoped to the component and do not interfere with other parts of the application.

function Button({ children }) {
  return (
    <button>
      {children}
      <style jsx>{`
        button {
          background-color: #0070f3;
          color: white;
          border: none;
          padding: 20px 30px;
          border-radius: 5px;
          font-size: 16px;
          cursor: pointer;
        }
        button:hover {
          background-color: #0051a2;
        }
      `}</style>
    </button>
  )
}

In this example, the CSS defined within the <style jsx> tag applies only to the button element within this component, ensuring that styles are modular and do not affect other parts of the application.

13. What Is Client-Side Rendering?

Client-Side Rendering (CSR) leverages JavaScript to render websites or applications directly in the browser, processing and displaying content on the client side rather than on the server. With CSR, the server sends a minimal HTML document with links to JavaScript files, which the browser then fetches, processes, and uses to render the content on the page.

The best JavaScript frameworks like React.js, Vue.js, Angular, Backbone.js, Ember.js, and Svelte are popular for handling client-side rendering. Understanding CSR is crucial for both front-end and back-end developers, as it helps answer Next.js interview questions. CSR contrasts with server-side rendering and significantly impacts how applications are built and optimized.

14. What Are Environment Variables in Next.js?

Environment variables in Next.js are used to manage configuration settings and sensitive information across different deployment environments. They allow developers to configure applications without hardcoding sensitive data or environment-specific settings directly into the source code.

In Next.js, environment variables are managed using an .env.local file. This file loads variables into the Node.js process, making them accessible during server-side operations. They can be utilized in data fetching methods such as getServerSideProps, getStaticProps, getStaticPaths, or within API routes.

Next.js typically uses a single .env.local file for managing environment variables. However, if you need different settings for various environments, you can configure them as needed. Next.js supports three main environments:

• Development environment
• Production environment
• Test environment

15. What Is Static Site Generation in Next.js, and When Would You Use It?

Static Site Generation (SSG) in Next.js is a powerful feature that transforms how websites are built and served. At its core, SSG is about creating HTML files in advance rather than generating them on-demand for each user request.

When you use SSG in Next.js, you're essentially pre-rendering your entire website during the build process. This means that instead of constructing pages dynamically for each visitor, your server can simply serve pre-built HTML files. This approach significantly reduces the server's workload and speeds up content delivery.

You would use static site generation in Next.js when:

• The content of your pages doesn't change frequently.
• You can determine the necessary pages at build time.
• You want to improve performance by serving pre-rendered content.
• SEO is a priority, as static pages are easily crawlable.

SSG is commonly used in blogs, marketing websites, product pages, and documentation sites. Having a basic understanding will help you clear your interview, as it demonstrates your knowledge of optimizing performance and managing content in a static context.

16. What Is the Difference Between Next.js and Create React App?

Next.js offers server-side rendering and static site generation out-of-the-box, providing enhanced performance and SEO benefits, whereas Create React App focuses solely on client-side rendering. This topic is major in Next.js, and it often appears in Next.js interview questions.

Below are the highlighted differences between Next.js and Create React App:

17. How Do You Handle Data Fetching in Next.js?

In Next.js, data fetching is managed through three main methods:

• getStaticProps: Preloads data at build time and generates static pages, enhancing performance and SEO by serving pre-rendered pages. It’s used for Static Site Generation (SSG) and Incremental Static Regeneration (ISR).
• getStaticPaths: Works with getStaticProps for dynamic routes, specifying which paths to pre-render at build time.
• getServerSideProps: Fetches data and generates pages on each request, making it suitable for real-time data but slower compared to getStaticProps. It’s used for Server-Side Rendering (SSR).

These methods are crucial topics for Next.js and are often featured in Next.js interview questions, as they highlight how to optimize data fetching and page rendering for various scenarios.

18. What Is the Purpose of the _app.js File in Next.js?

The _app.js file in a Next.js application serves as a global wrapper for all pages. It is used to apply global CSS, integrate layout components, and provide context providers, ensuring consistent features and functionalities across the entire application. Every page request triggers this file, making it central to managing global settings and behaviors.

19. What Are the Main Scripts in Next.js?

In Next.js, the main scripts are defined in the package.json file and are crucial for different stages of the application lifecycle. They include:

• dev: Runs the application in development mode with features like hot reloading and detailed error messages. It is executed using the command next dev.
• build: Compiles the application for production deployment. This script optimizes and bundles the code, generating static assets and optimizing performance. It is executed using the command next build.
• start: Starts the application in production mode, serving the compiled build. This script is used to run the optimized version of the application after building it. It is executed using the command next start.

These scripts are fundamental for developing, building, and deploying Next.js applications.

The Next.js interview questions covered above are fundamental and essential for any fresher to know, as they form the basic foundation of understanding Next.js features and functionality. Mastering these basics is crucial for building a strong Next.js skill set and performing well in interviews.

As you progress, you will learn intermediate-level Next.js interview questions to deepen your knowledge and enhance your expertise. This will help you tackle more complex topics and scenarios, advancing your skills in the field.

These Next.js interview questions cover advanced topics and are ideal for candidates with some experience in the framework. They are designed to test your ability to handle complex scenarios and optimize operations, helping you further enhance your skills.

20. What Is the Purpose of the getStaticPaths Function in Next.js?

The getStaticPaths function in Next.js is used to generate static pages for dynamic routes during the build process. It allows you to specify which dynamic routes should be pre-rendered ahead of time based on a list of paths.

In Next.js, dynamic routes are defined using square brackets in filenames (e.g., [ID].js), which creates routes like user/[ID]. The getStaticPaths function enables you to pre-generate static pages for each of these routes by returning an object containing two properties:

• paths: An array of objects specifying the dynamic parameters for each route to be pre-rendered.
• fallback: Determines how Next.js should handle paths not included in the paths array. It can be:
• false: Returns a 404 page for undefined paths.
• true: Generates the page on-demand if a requested path is not pre-rendered.

Here's a basic example of how getStaticPaths is used:

export async function getStaticPaths() {
    // Define the paths to pre-render
    const paths = [
        { params: { id: '1' } },
        { params: { id: '2' } },
        { params: { id: '3' } }
    ];
    return {
        paths,
        fallback: false
    };
}

The above setup will pre-render static pages for user/1, user/2, and user/3 at build time.

21. How Do You Work With Custom Server Middleware in Next.js?

Custom server middleware in Next.js is configured by creating a server.js file at the root of your project. This file allows you to set up a custom Node.js server using Express or another Node.js server framework. Middleware functions are added using the use method to handle requests and responses before they reach your Next.js application routes.

22. What Is the Purpose of the useEffect Hook in React, and How Does It Relate to Next.js?

The useEffect hook in React is essential for managing side effects in functional components, such as API data fetching, updating the document title, or handling timers. In a Next.js application, useEffect is particularly useful for client-side data fetching and interacting with browser-specific features, as it runs only on the client side after the initial render.

This question has often been asked during your Next.js interview questions, as it highlights your ability to manage client-side operations effectively in a server-side rendered framework.

23. What Do You Understand by Code Splitting in Next.js?

In Next.js, code splitting is a powerful feature that allows you to divide your JavaScript code into smaller chunks or bundles, which are then loaded on-demand or in parallel.

This technique, often facilitated by Webpack, helps improve page load times by ensuring that users only download the necessary code for the page they're viewing.

Mastery of code splitting is crucial under Next.js topics, and it is often asked during Next.js interview questions, as it demonstrates your understanding of optimizing application performance and resource management.

24. How Do You Optimize the Performance of a Next.js Application?

To optimize the performance of a Next.js application, consider the following techniques often discussed in Next.js interview questions:

• Multi-Zones: Deploy multiple Next.js applications as a unified app to manage large-scale projects or separate concerns among different teams. This approach ensures a seamless user experience while maintaining development separation.
• Dynamic Imports: Split your code into smaller chunks with dynamic imports, loading only the necessary parts on-demand to improve load times.
• Route-Based Splitting: Next.js automatically performs code splitting for each route, ensuring that only the code required for the current page is loaded, which reduces initial load times.
• Component-Based Splitting: Use dynamic imports for large or complex components that are not immediately needed, loading them only when required or after user interaction.
• Delay Non-Essential Scripts: Manage third-party scripts efficiently using the Next/script component, with strategies like beforeInteractive, afterInteractive, or lazyOnload to control loading behavior.
• Caching: Implement custom caching strategies for dynamic content using API routes or server-side props. Next.js already adds caching headers to static assets for better performance.
• Incremental Static Regeneration (ISR): Update static content without rebuilding the entire site by specifying a revalidation period, allowing Next.js to regenerate pages in the background.
• Bundle Analysis: Use the @next/bundle-analyzer package to identify large dependencies or unnecessary imports that may affect performance.
• Personalization: Utilize edge middleware to handle requests, set headers, or generate responses close to your users, enhancing personalization while maintaining performance.
• Micro Frontends: Implement micro frontends using Webpack's Module Federation to develop, deploy, and scale different parts of your application independently, improving both development efficiency and performance.

25. Explain the Purpose of the getServerSideProps Function.

The getServerSideProps function in Next.js plays a crucial role in server-side rendering (SSR) by allowing you to fetch data on the server for each page request. This function runs on the server for every incoming request, ensuring that the page is pre-rendered with the most current data before being sent to the client.

It is especially useful for pages that need to display frequently updated content or depend on data from external sources. By using getServerSideProps, you can provide users with real-time information, enhancing the dynamic nature of your application and ensuring they always see the latest updates.

26. What is the Purpose of the next.config.js Excludes Property?

In next.config.js, the excludes property is used to specify files and directories that should be excluded from Next.js's default code splitting and bundling processes. This feature is essential for managing which resources are omitted from the automatic optimization provided by Next.js.

Understanding and using the exclude property can be a key topic in Next.js interview questions, as it helps tailor performance and bundling strategies to your application's specific requirements.

27. Explain the Purpose of the next.config.js Headers Property.

In next.config.js, the headers property allows you to define custom HTTP headers for responses served by your Next.js application. This configuration helps you manage aspects such as caching policies, security settings, and other custom requirements to control how clients and browsers handle your content.

Understanding and effectively using the headers property can be crucial for optimizing performance and security, making it a relevant topic to be asked during Next.js interview questions.

28. What is the Purpose of the next.config.js Experimental Property?

The experimental property in next.config.js serves two main purposes in Next.js:

• Accessing Pre-Release Features: This property allows you to enable and test new, experimental features before they are officially released. By configuring specific flags within the experimental, you can explore upcoming capabilities, provide feedback, and influence their development before their official launch.
• Customizing Advanced Settings: It also provides access to advanced configurations that let you fine-tune performance, experiment with alternative build processes, or adjust internal behaviors. These settings are intended for experienced developers who need deeper control over Next.js and are willing to manage the potential risks associated with using experimental features.

Understanding and using the experimental property effectively is important for those looking to stay ahead with Next.js advancements, and it often appears in Next.js interview questions.

29. What is the Purpose of the next.config.js Redirects Property?

The redirects property in next.config.js is used to set up server-side redirects for incoming requests in Next.js. This configuration simplifies the process of directing users and search engines to different URLs without relying on client-side routing or additional server-side logic.

• Asynchronous Setup: Configured as an asynchronous function that returns an array of redirect objects, each defining a redirection rule.
• Server-Side Handling: Redirects are processed on the server, ensuring consistent behavior across all browsers and devices, even if JavaScript is disabled.
• Redirect Types: Supports both temporary (307) and permanent (308) redirects based on your requirements.
• Advanced Conditions: Allows for complex redirect rules based on headers, cookies, query parameters, and more, offering precise control over redirections.

Understanding how to use the redirects property is crucial for managing URL changes and redirections effectively, making it a relevant topic to appear in Next.js interview questions.

30. What is the Purpose of the next.config.js Rewrites Property?

The rewrites property in next.config.js allows you to customize the handling of incoming server requests without changing the URL seen by the client. This property is particularly useful for:

• URL Redirection: Mapping requests to different internal paths or external URLs while keeping the client’s URL unchanged.
• Content Delivery: Serving different content based on specific conditions, such as environment variables or request headers.
• Endpoint Mapping: Redirecting requests to alternative endpoints, enabling flexible routing and content management.

Unlike redirects, which alter the URL in the browser, rewrites modify request processing internally while maintaining the original URL visible to the user. This is a key feature for advanced routing scenarios and is a relevant question that appears often in Next.js interview questions.

31. Describe Scenarios Where You Would Choose to Use getStaticProps Over getServerSideProps and Vice Versa.

Choosing between getStaticProps and getServerSideProps depends on the nature of your page’s data and update frequency:

Use getStaticProps when:

• Content is Static: Ideal for pages with static content that doesn't change often, such as blog posts, product catalogs, or documentation. This method pre-renders pages at build time, leading to faster load times and better SEO.
• High Traffic Sites: Static pages can handle high traffic efficiently since they serve as pre-built HTML, reducing server load.

Use getServerSideProps when:

• Dynamic Data: Best for pages requiring real-time data or personalized content, such as dashboards, user profiles, or pages with frequently updated information. It renders pages on the server per request, ensuring the data is always fresh.
• User-Specific Content: Essential for scenarios involving user authentication or content specific to individual users, where data needs to be fetched and processed on each request.

In summary, getStaticProps excels with static, infrequently changing content, providing performance benefits. In contrast, getServerSideProps is suited for dynamic or personalized data that requires real-time updates, though it may have a performance trade-off due to server-side rendering on each request.

32. Explain the Purpose of the Next Export Command. When Would You Use It, and What Are Its Limitations?

The next export command generates a static HTML version of your Next.js application, allowing it to be deployed without a Node.js server. It is used when you want to deploy as a static site and don't need server-side rendering or dynamic routes. Its main limitation is that it does not support dynamic routes or server-side features.

33. What Is the Difference Between an App Router and a Pages Router?

In Next.js, an App Router handles routes using the new App Directory approach, providing advanced features and flexibility. In contrast, the Pages Router relies on the traditional file-based routing system. Understanding these differences is crucial as they are important aspects of Next.js, and this question often appears in Next.js interview questions.

Here's the difference between App Router and Pages Router in Next.js:

34. Explain the Purpose of the publicRuntimeConfig and serverRuntimeConfig Options in Next.js

The publicRuntimeConfig and serverRuntimeConfig options in Next.js manage runtime configurations with distinct scopes of accessibility.

• serverRuntimeConfig: It is for server-side use only, ideal for sensitive information like API keys or database credentials. It ensures these values remain secure, as they are not exposed to the client.
• publicRuntimeConfig: It is accessible on both the server and client sides, suitable for public information like API endpoints or feature flags. However, it should not contain sensitive data, as it will be visible to users.

Both options are configured in next.config.js and accessed via getConfig() from next/config. This setup allows for dynamic, environment-specific configurations without requiring application rebuilds.

Understanding these configurations is crucial for Next.js users, and this question often appears in Next.js interview questions as it highlights how to handle environment-specific settings effectively.

35. Explain Image Optimization in Next.js

Next.js offers an Image component that automatically optimizes images for better performance and user experience. This component provides properties to control image loading (loading or priority), size and layout (width, height, layout), and placeholders (placeholder, blurDataURL). These features help improve loading times and visual stability by efficiently handling image rendering and responsiveness.

Some of the Image components are mentioned below that help image optimization in Next.js:

• Image Loading Behavior: The 'loading' property controls how images load. By default, it uses "lazy" loading, which loads images as they become visible during scrolling. For crucial images, you can use "eager" loading or the 'priority' property.

Example:

<Image 
  src="/example.png" 
  alt="Example" 
  width={500} 
  height={300}
  loading="eager"
  // or
  priority={true}
/>

• Image Sizing and Layout: Always specify image dimensions to improve Cumulative Layout Shift (CLS). If dimensions are unknown, use 'layout="fill"', which makes the image respond to its parent container's dimensions. The 'layout' property offers four options: "fill", "intrinsic", "responsive", and "fixed".

When using 'layout="fill"', the 'objectFit' property determines how the image resizes within its container. Options include "contain", "cover", "fill", and "none".

Example:

<Image 
  src="/example.png" 
  alt="Example" 
  layout="fill"
  objectFit="contain"
/>

• Placeholders and Loading Indicators: The 'placeholder' property allows for a temporary image or loading indicator while the main image loads. It can be set to "blur" or "empty". When using "blur", you can provide a base64-encoded image as a blurred placeholder.

Example:

<Image 
  src="/example.png" 
  alt="Example" 
  width={600}
  height={450}
  placeholder="blur"
  blurDataURL="data:image/png;base64,..."
/>

• Image Quality: The 'quality' property allows you to set the image quality, with values ranging from 1 to 100. The default is 75.

Example:

<Image 
  src="/example.png" 
  alt="Example" 
  width={500}
  height={550}
  quality={100}
/>

36. What are Cross-Origin Requests (CORS)?

Cross-Origin Resource Sharing (CORS) is a web security feature that controls which origins can access resources on a server. An origin is defined by the combination of protocol, domain, and port in a web request.

CORS is designed to enhance security by preventing unauthorized access to resources across different origins. The process involves an exchange of specific HTTP headers between the browser and the server.

For some cross-origin requests, the browser first sends a "preflight" request using the HTTP OPTIONS method to check if the server allows the request. If the server's CORS headers approve the preflight request, the actual request is sent. If not, the browser blocks the request, leading to a CORS policy error.

Understanding CORS is crucial for Next.js application developers, as it often appears in Next.js interview questions related to managing security and resource access.

37. Why Do You Need CORS With Next.js?

Next.js supports API development out-of-the-box, but by default, its APIs follow a same-origin policy, meaning they don't include CORS (Cross-Origin Resource Sharing) headers. This restricts access to these APIs to requests originating from the same domain.

However, if you need to access these APIs from different origins—such as when your application is hosted on a separate domain—you'll face cross-origin restrictions. To enable cross-origin access, you need to configure CORS by setting up the appropriate headers on your Next.js server.

Once CORS is correctly configured, your APIs can be accessed from approved domains, facilitating more flexible interactions between your Next.js APIs and other applications. Understanding CORS in Next.js is important for handling cross-origin requests, and this topic frequently appears in Next.js interview questions.

The intermediate-level Next.js interview questions listed above are designed to help both beginners and those with some experience prepare effectively for interviews. As you advance, you will encounter more challenging Next.js interview questions that are particularly relevant for experienced developers.

Here, the focus shifts to advanced topics essential for experienced Next.js developers. By exploring these advanced Next.js interview questions, you will gain a comprehensive understanding of complex Next.js features and optimization strategies, equipping you to handle complex development scenarios and build high-performance applications effectively.

38. How Would You Approach Migrating a Traditional React App to Next.js?

To migrate a traditional React app to Next.js:

• Set Up Next.js: Create a new Next.js project using create-next-app.
• Move Components: Transfer your existing React components into the Next.js project, placing them in appropriate directories such as components and pages.
• Adjust Routing: Update routing to fit Next.js’s file-based routing system, where the file structure in the pages directory determines the routes.
• State Management: Continue using your current state management solution like Redux, or explore Next.js’s data fetching methods like SWR for managing state.
• Testing: Test the application thoroughly to ensure all features and functionalities work as expected in the new Next.js environment.

39. What Strategies Do You Use to Ensure a Secure Next.js Application?

Here are some strategies to ensure a secure Next.js application, which are often highlighted in Next.js interview questions:

• Use HTTPS: Ensure all communication is encrypted by configuring SSL/TLS certificates and redirecting HTTP requests to HTTPS, either through server configuration or the next.config.js file.
• Implement Authentication and Authorization: Use secure methods like JWT for authentication, integrate with trusted providers, and apply role-based access control to manage permissions effectively.

Protect Against Common Vulnerabilities:

• Content Security Policy (CSP): Implement CSP headers to mitigate XSS attacks.
• CSRF Protection: Utilize Next.js’s built-in CSRF protection.
• Sanitize User Inputs: Guard against SQL injection and other injection attacks by validating and sanitizing inputs.
• Secure HTTP Headers: Use libraries like helmet.js to set secure HTTP headers.

These practices help to build a robust and secure Next.js application, protecting it from common threats and ensuring data integrity and confidentiality.

40. How Would You Implement Server-Side Rendering (SSR) for a Next.js Page?

To implement Server-Side Rendering (SSR) for a Next.js page:

• Create a Page Component: Define your page in the pages directory.
• Export getServerSideProps: Create an asynchronous function called getServerSideProps in the same file.
• Fetch Data: Inside getServerSideProps, retrieve the necessary data.
• Return Data: Return an object with a props key containing the fetched data.
• Use Props: Utilize the returned props in your page component to render the content.

Example:

  // pages/ssr-page.js
  export async function getServerSideProps(context) {
    const res = await fetch('https://api.example.com/data');
    const data = await res.json();
  
    return {
      props: { data }, // Will be passed to the page component as props
    };
  }
  
  function SSRPage({ data }) {
    return <div>Server-side rendered data: {data}</div>;
  }
  
  export default SSRPage;

41. What is Docker Image in Next.js?

A Docker image for a Next.js application is a self-contained package that includes the application code, runtime environment, libraries, and system tools required to run the app. It provides a consistent, immutable snapshot of your application’s environment, ensuring that it behaves the same way regardless of where it is deployed.

In Docker terminology, if an image is analogous to a class in object-oriented programming, then a container is like an instance of that class. Containers are the live, running instances created from Docker images.

The main purpose of using Docker with Next.js is to facilitate consistent, portable deployments. By building a Docker image of your Next.js application, you ensure that it runs in the same way across different environments. Once the image is created, you can deploy it to various environments, such as development, staging, or production, with confidence that the application will function consistently.

42. How Do You Handle Error Pages in Next.js?

Next.js offers a flexible approach to managing error pages through the creation of a pages/_error.js file. This file serves as a universal error handler for your application.

Here's how you can implement it:

  function Error({ statusCode }) {
    return (
      <p>
        {statusCode
          ? `A ${statusCode} error occurred on the server`
          : 'An error happened on the client'}
      </p>
    );
  }
  
  Error.getInitialProps = ({ res, err }) => {
    const statusCode = res ? res.statusCode : err ? err.statusCode : 404;
    return { statusCode };
  };
  
  export default Error;

This setup allows for dynamic error handling. The component checks whether the error originated on the server (with a status code) or the client and displays an appropriate message. It uses getInitialProps to retrieve the error's status code, defaulting to 404 if no specific code is available.

43. Explain the Importance of Code Splitting in Next.js

Code splitting is important in Next.js because:

• Code splitting allows Next.js to break your application into smaller chunks. Instead of loading the entire application at once, only the necessary code for the current page or component is loaded.
• By splitting the code, your application's overall bundle size is reduced. This is particularly beneficial for users with slower internet connections or mobile devices, as they don't need to download unnecessary code.
• With smaller chunks of code loaded, the browser can parse and execute JavaScript faster, improving overall application performance.
• Smaller, separated chunks of code are easier to cache effectively. When updates are made to specific parts of your application, users need to re-download only those chunks rather than the entire application bundle.
• Code splitting aligns with modern web development practices, using features like lazy loading and dynamic imports to create more efficient applications.

44. How to Setup CDN in Next.js?

To set up and use a Content Delivery Network (CDN) with asset prefixing in Next.js, configure the assetPrefix property in the next.config.js file. This property lets you specify a base URL for all static assets in our application, effectively routing them through our chosen CDN.

Let's consider different scenarios for setting up a CDN:

• Basic CDN setup:

  
        // next.config.js
        module.exports = {
          // Set assetPrefix to the base URL of your CDN
          assetPrefix: 'https://cdn.example.com',
        }
      

• Environment-specific CDN:

  
        // next.config.js
        module.exports = {
          assetPrefix: process.env.NODE_ENV === 'production' 
            ? 'https://prod-cdn.example.com' 
            : '',
        }
      

• CDN with a specific path:

  
        // next.config.js
        module.exports = {
          assetPrefix: 'https://cdn.example.com/my-nextjs-app',
        }
      

Once we have set the assetPrefix property, all asset URLs in our application (including images, JavaScript files, and CSS files) will be automatically prefixed with the specified URL.

For instance, if we have an image file named logo.png in our public directory:

• Without CDN: /_next/static/images/logo.png.
• With CDN: https://cdn.example.com/_next/static/images/logo.png.

This prefixing applies to all static assets managed by Next.js, ensuring they are served from your configured CDN rather than your main server. This can significantly improve load times and reduce the burden on your primary server, especially for users geographically distant from your main server location.

45. What Is Serverless Architecture, and How Does It Relate to Next.js?

Serverless architecture refers to building and running applications without the need to manage the infrastructure. The term "serverless" is somewhat deceptive because servers are still in operation, but the cloud provider manages them, automatically adjusting resources based on demand.

To utilize serverless architecture with Next.js, consider deploying your application on serverless platforms like AWS Lambda or Google Cloud Functions. This approach allows for efficient use of resources and automatic scaling based on varying workloads.

Additionally, to ensure your Next.js application performs optimally in different environments, you can make use of a cloud-based platform that will help you ensure your Next.js application performs optimally across different environments, browsers, and devices.

One such cloud platform is LambdaTest. It is an AI-powered test execution platform that lets you conduct manual and automated Next.js testing at scale on a remote test lab of 3000+ browsers and OS combinations.

LambdaTest helps in identifying and fixing issues related to browser compatibility and responsiveness, ensuring that your Next.js application delivers a consistent and reliable user experience, regardless of where or how it is accessed.

46. Explain How to Internationalize a Next.js Application to Support Multiple Languages

Starting from version 10.0.0, Next.js has introduced native support for internationalized (i18n) routing. It allows you to define locales, set default locale settings, and specify domain-specific locales, with Next.js managing the routing automatically.

When a user visits the root of the application (represented by the '/' path), Next.js employs an intelligent detection mechanism. It analyzes two primary factors to determine the user's preferred locale:

• The Accept-Language header: Indicates the user's language preferences as set in their browser.
• The current domain: From which the user is accessing the application.

Based on this analysis, if Next.js detects that the user's preferred locale differs from the default locale set for the application, an automatic redirection process will be initiated. The redirection behavior varies depending on the routing strategy employed:

• Domain Routing Strategy: Uses different domains or subdomains for different languages. For example, a user accessing "example.com/browse" might be redirected to "example.es/browse" if Spanish is detected as their preferred language.
• Sub-path Routing Strategy: Uses URL path prefixes to differentiate between languages. For example, a user visiting "example.com/browse" might be redirected to "example.com/es/browse" if Spanish is the detected preferred language.

This automated system detects the user's language and redirects them to the right content without any manual effort.

47. Explain the Concept of “Prefetching” in Next.js and How It Impacts Performance

In Next.js, the prefetching mechanism works by automatically downloading JavaScript and assets for linked pages in the background. This proactive measure cuts down navigation time, leading to smoother and faster transitions between pages, enhancing the user experience.

The impact of prefetching on performance is significant:

• When a user clicks a prefetched link, the page transition is nearly instantaneous because the necessary code is already loaded.
• Users experience smoother navigation, giving the impression of a faster, more responsive application.
• By distributing the loading of resources over time, prefetching can help balance server load.
• Next.js is intelligent about prefetching, only doing so for pages in the viewport and during idle times.

48. Explain Next.js Authentication

Authentication is the process of confirming a user's identity by asking for credentials, like a username and password. The concept of authentication is consistent among JavaScript frameworks, including Next.js.

Next.js Authentication process:

Next.js provides various strategies for managing this essential security function. Here's the process:

• Request initiation: Starts when a user tries to access a secure page, potentially redirecting them to a login page if not authenticated.
• Data submission: Users enter their credentials or use third-party authentication methods like Google or Facebook.
• Verification: Next.js verifies credentials with backend services or third-party services like NextAuth.js or Passport.js.
• Session creation: After successful authentication, a session cookie is created, allowing access to protected areas without re-authentication.
• Access or denial: Depending on the credentials, the user is granted or denied access.
• Middleware integration: For more control, middleware like Passport.js can be used to manage authentication flow.

49. What Is the Difference Between Authentication and Authorization?

Authentication verifies the identity of a user or system, answering "Who are you?" Authorization determines what an authenticated user is allowed to do, answering "What can you do?"

Understanding the concepts of Authentication and Authorization is crucial for developers working on Next.js applications, and these topics often appear in Next.js interview questions.

Below are the differences between Authentication and Authorization:

50. Explain Incremental Static Regeneration (ISR) in Next.js

Incremental Static Regeneration (ISR) is a Next.js feature that creates static pages with incremental updates after generation, combining the advantages of SSG and SSR. It permits static content to update gradually over time without needing a total site rebuild, as traditional SSG requires.

This technique is perfect for pages that display somewhat dynamic data but don't require updates with each request. ISR provides the speed of a static site and the flexibility of server-rendered content to users.

ISR (Incremental Static Regeneration) operates in two main scenarios:

• On initial request: The page is created on-the-fly, similar to Server-Side Rendering (SSR). However, this generated page is then stored in the cache for future visitors, mimicking Static Site Generation (SSG). This ensures quick loading for subsequent users.
• On subsequent requests: Users receive the cached version immediately. Meanwhile, Next.js checks if it's time to update the page. If so, it rebuilds the page on the server and replaces the older version in the cache.

The primary benefit of ISR is that users always get a fast-loading page. They either see the cached content right away or the freshly updated version if it's already been regenerated. Understanding ISR is crucial for handling dynamic content in Next.js applications, and is a common topic in Next.js interview questions.

Mastering Next.js is essential for modern web developers, especially those experienced with React. This list of Next.js interview questions spans basic to advanced Next.js concepts. Understanding these principles and applying them to real-world projects will enhance your proficiency. Stay updated on Next.js developments and continuously refine your skills to excel in interviews and practical applications.

Best of luck!