Top 50 Next.js Interview Questions & Answers [2024]

Next.js is an advanced, powerful React framework that improvises web development by using server-side rendering, static site generation, and other key features. As it continues to gain popularity, any developer needs to truly understand the core concepts and best practices. Learning Next.js is a must for developers looking to build highly optimized and performant web applications.

In this regard, we have compiled a set of Next.js interview questions useful for conducting an interview. These questions range from the fundamentals, such as basic concepts and core principles, to advanced techniques that actually help to prepare someone enough for a forthcoming interview. Be it a new developer or an expert developer in this technology; it will help to keep you a step ahead in the competitive job market.

Next.js Interview Questions For Freshers

1. What is Next JS?

Next.js is Vercel's open-source web development React-based framework, famous because of its special features, which are server-side rendering and improved SEO. Further extended features include data fetching utilities, dynamic API routes, optimized builds, and many more. It is a framework built on top of React, Webpack, and Babel.

2. How does NextJS differ from other JavaScript frameworks?

Next.js is a JavaScript framework primarily used for building React applications. Some of the key aspects in which Next JS differs significantly from the other available JavaScript frameworks are:

• Server-Side Rendering: It is one of the significant features that can be called an improvement on many other similar frameworks; Next JS has the inbuilt option to support server-side rendering, meaning rendering pages on the server rather than on the client, which brings out some other advantages, such as better SEO or faster first page loads.
• Automatic Code Splitting: Next.js does it natively. It efficiently enables the splitting of code into smaller chunks of JavaScript, which loads only the part related to the user's current page.
• API Routes: Make API routes inside the same project easily for easy backend functionality in concurrence with the front end.
• Built-In Image Optimization: Next.js is supposed to have an in-built image optimization through its next/image component. It's going to manage lazy loading along with responsive images by itself. No extra configuration will be needed.
• Easy Deployment: Next.js makes deployment very easy with a lot of diverse options. They range from static site hosting to serverless deployment and many others. This ease of deployment is not always as straightforward in other frameworks.

3. What is the process of installing Next JS?

Below is the step-by-step process of installing the Next JS:

Steps to Install the Next JS:

Step 1: Node JS should be already installed in the system.

Step 2: Now create the next js app using the below command:

npx create-next-app myapp

Step 3: Now switch to the project directory:

cd myapp

Step 4: Next JS app is initialized by updating the package.json:

{
“scripts”: {
“dev”: “next”,
“build”: “next build”,
“start”: “next start”
}
}

4. How to Create a New Next.js App?

Setting up a new application with Next.js can be done with the help of the command create-next-app. For example, you can execute something like this in the terminal: npx create-next-app my-app. This will install the Next.js setup for a new application and name it—in the above case—as my-app.

5. What is server-side rendering, and why do we need it?

SSR is a process whereby every web page is first rendered in the server before being sent to the client's browser. Had to define SSR with just one word, important would be it, since it will let search engines like Google crawl and index your website content, hence probably improving the SEO of the website. More importantly, SSR can further improve the page load time at the beginning and enhance user experience.

6. What is client-side rendering, and how is it different from server-side rendering?

CSR is a process of rendering a web page in a client's browser using JavaScript. This happens immediately after receiving the first response of HTML, CSS, and JavaScript from the server. An important difference between SSR and CSR is that SSR sends an already rendered HTML page to the client's browser, whereas CSR sends out a lightly loaded or empty HTML page, which becomes populated with JavaScript.

7. Mostly for which type of websites is Next JS used?

Several types of websites and applications can be built. But the most popular are-

• Desktop websites
• Static websites
• Server rendered applications
• SEO friendly websites
• Progressive Web Applications (PWA)

8. Mention the three main ways to split code.

Three main ways to split code are given below-

1. Entry Points- In this method, configurations need to be entered manually.
2. Prevent Duplication- SplitChinksPlugin or Entry dependencies are used here for splitting chunks.
3. Dynamic Imports- The code is split using inline function calls within the modules.

9. Explain how data fetching works in Next.js and mention the key methods.

Data fetching in Next.js can be done during server-side rendering or client-side rendering. Two key methods for data fetching are:

- getServerSideProps: This method is used for server-side rendering. It fetches data on every request and returns it to the page component as props.

- getStaticProps: This method is used for static generation. It fetches data at build time and is useful for content that doesn't change frequently.

10. How do you pass data between pages in a Next.js application?

Next.js provides a few ways of data sharing between different pages of your Next.js app: by URL query parameters, using the Router API, or state management libraries such as Redux or React Context. You can also fetch it on the server with getServerSideProps and pass it as props to the page component.

11. What are some of the major companies that use Next JS?

Some of the major companies that use Next JS are given below-

• TikTok
• Nike
• Netflix Jobs
• GitHub Copilot
• Target
• Twitch

12. What is the _app.js file used for in Next.js?

The `_app.js` file wraps the entire application and is used to add global styles, layout components, and context providers. The file is called for every page request. This is where common functionality to applications can be added.

13. How do you handle Authentication in a Next.js application?

Authentication in Next.js can be done using multiple available options, including JSON Web Tokens-based, OAuth-based, and third-party libraries like NextAuth.js. You could also do server-side authentication using server-side rendering and session management.

14. How do you configure and use CSS modules in Next.js while styling your application?

You simply create a file with a .module.css extension for a CSS file and import it into your components. You will then be able to use these styles as an object in your JSX.

For example:

import styles from './styles.module.css';
function MyComponent() {
return <div className={styles.myStyle}>Styled content</div>;
}

15. Handling errors in a Next.js application?

Next.js provides several ways to handle errors: through custom error pages, getInitialProps error handling at the server side, and React error boundaries at the client side. It further enables one to use a third-party library such as Sentry or Rollbar for error monitoring and reporting.

16. What is the difference between a container component and a presentational component?

In contrast, a container component is responsible for handling state and logic; a presentational component cares only about returning the UI with props passed down from a higher-order container component.

17. What is the purpose of the useEffect hook in React, and how does this apply in Next.js?

One of the major means through which side effects are treated in functional components is the useEffect hook. For example, fetching data from an API or updating the document title. In Next.js, many kinds of client-side data fetching can be carried out with the fetch API or libraries like Axios or SWR with the useEffect hook.

18. How do you internationalize a Next.js application to support multiple languages?

You can implement i18n in Next.js by using third-party libraries such as Next-i18next, amongst others. This will involve handling translation of text and content, language-based routing, and the switching mechanism between languages for users. Proper i18n will give your application the ability to be used globally.

19. What are the _app.js and _document.js?

The file _app.js can be used to make the top-level component of your Next.js application customizable by adding global CSS styles, layout components, or shared context providers. The _document.js file is used for customizing the HTML and body elements of the application and is often used for adding third-party scripts or metadata.

20. What are Environment Variables in Next JS?

Next.js is equipped with native support for managing environment variables, providing the following capabilities:

• Utilize .env.local for loading environment variables.
• Expose environment variables to the browser by prefixing them with NEXT_PUBLIC_.
• Default Environment Variables: Typically, only one .env.local file is required. However, there may be instances where you want to establish defaults specifically for the development (next dev) or production (next start) environment.
• Next JS enables you to define defaults in .env (applicable to all environments), .env.development (specific to the development environment), and .env.production (specific to the production environment).
• It’s important to note that .env.local always takes precedence over any defaults that are set.

21. What is Docker Image in Next JS?

Next JS is deployable on hosting providers that offer support for Docker containers. This approach is applicable when deploying to container orchestrators like Kubernetes or HashiCorp Nomad, or when operating within a single node on any cloud provider.

To implement this deployment method:

• Install Docker on your machine.
• Clone the example named with-docker.
• Build your container using the command: docker build -t nextjs-docker.
• Run your container with the command: docker run -p 3000:3000 nextjs-docker

22. What is "Prefetching" in Next JS, and how does it affect performance?

Prefetching in Next.js is a mechanism through which the framework makes an automated initiation to start downloading JavaScript and assets for linked pages in the background. In doing this proactively, the navigation time could be significantly reduced; hence, providing seamless interaction to the end-user by fast transitioning among pages.

23. How do you internationalize a Next JS app for multiple languages?

Next.js supports internationalization either through libraries like next-i18next or by writing a custom solution. This typically involves the translation of text and content, handling routes based on languages, and probably adding a mechanism that enables a user to switch between languages easily. Proper i18n techniques make sure users from all around the world are catered to in your application.

24. What is the purpose of the component next/head in Next.js?

The next/head component enables editing of the <head> section of your HTML document. It adds dynamic elements like meta tags, title, and link tags.

25. How is a custom 404 page created in Next.js?

Answer: Next.js allows the creation of custom 404 pages by simply adding a 404.js to the pages directory. The content of this page will then be shown when a route doesn't match any existing page.

Next.js Interview Questions For Experienced

1. Which method does Next JS recommend for fetching data?

Next JS provides several methods for fetching data. But the one that it recommends is getInitialProps. It is an async function using which data can be retrieved from anywhere.

2. What are the properties available in a context object that arises on using getInitialProps?

The following properties are there-

1. Pathname- The path section of the URL is specified.
2. asPath- A string of the actual path that is shown in the browser is specified.
3. Query- It specifies the query string section that is parsed as an object.
4. Req- It specifies the HTTP request object (server only).
5. Res- It specifies the HTTP response object (only server)
6. Err- It specifies the error object in case any error is found while rendering.

3. How do you ensure that a Next.js application runs with high performance?

There are quite a few ways to achieve performance optimization for a Next.js application. This is realized through code splitting, lazy loading, image optimization, server-side caching, and CDN caching. You can also use Lighthouse or WebPageTest performance monitoring tools at places where improvement is required.

4. How do you run serverless functions using a Next.js application?

Many people use Next.js in combination with a headless CMS for a straightforward and strong way to manage and utilize their content. Next.js supports serverless functions out of the box via the API Routes feature. You can then create a serverless function by making a file in pages/api within the name of the endpoint you want to hit and putting in the server-side logic.

5. How do you implement a headless CMS with Next.js?

Headless CMS can be implemented with Next.js through a third-party CMS like Contentful, Strapi, or Sanity. All these CMSs provide APIs to fetch and update content you can use in your Next.js pages with getStaticProps or getServerSideProps.

6. Differentiate between Next JS and Create-React-App.

7. Which key features are provided by Next JS in terms of SEO?

The following perks are there-

1. Jamstack compatibility
2. Increased flexibility in designing the UX of our website
3. Automatic static optimization
4. Improved data security
5. Fast static websites
6. Responsiveness and adaptability

8. How can build-id be configured in Next JS?

For configuring build-id in Next JS, a static ID must be configured between our build. Therefore, the ‘generateBuildId’ function must be provided with the given configuration -

// next.config.js
module.exports = {
generateBuildId: async () =>{
//For instance get the latest git commit hash
return ‘my-build-id’;
}
};

9. Explain the concept of "Serverless" deployment in the context of Next.js. How does it work, and what are the advantages?

Serverless deployment involves hosting your Next.js application on serverless platforms like Vercel or Netlify, where you don't manage any kind of traditional server infrastructure. These platforms automatically scale and handle server-side rendering, routing, and other aspects. The advantages include ease of scaling, cost efficiency, and simplified deployment.

10. How do you handle environment variables in Next.js?

Environment variables in Next.js are managed using .env files. You can create a .env.local file for local development, and use the NEXT_PUBLIC_ prefix to expose variables to the browser. Next.js automatically loads these variables into the process.env object.

11. How do you implement real-time updates in a Next.js application?

Next.js does not inherently support real-time updates. It could be realized with server-sent events, web sockets, or third-party libraries such as Socket.io to establish a live link between the client and the server for real-time notification of data updates in a Next.js application. You can leverage libraries such as react-use or redux to maintain real-time updates of data in the application.

12. How would you set up testing and configure continuous integration in a Next.js Project?

Testing and continuous integration directly in a Next.js application can be carried out using testing libraries/channels such as Jest or Cypress for writing and running tests. You may also use continuous integration services like CircleCI or Travis CI, which are automated testing and deployment services. Tools for code quality can be used to guarantee consistency and maintainability in the code through ESlint or Prettier.

13. How can different digital products be built using Next JS?

Several digital products can be built, such as:

• Jamstack websites
• Single web pages
• Minimum Viable Product (MVP)
• SaaS products
• Web portals
• Dashboards
• Retail and e-commerce websites
• User interfaces
• Complex web applications
• Static websites

14. Explain how you can implement user authentication and authorization in a Next.js application using third-party providers, like Google or Facebook.

You can implement authentication with third-party providers using OAuth2 or OpenID Connect. Libraries like next-auth or passport can simplify the process by handling the authentication flow and providing user data to your application.

15. Can you explain the benefits of using serverless functions with Next.js, and in what scenarios would you choose to implement them in your application?

Serverless functions in Next.js allow you to create lightweight, stateless API endpoints. They are particularly useful for handling dynamic data fetching, processing form submissions, and implementing backend logic in a serverless environment. You might choose to implement them in scenarios where you need server-side functionality without managing a traditional server.

16. What is static site export in Next.js and how do you use it?

Static site export generates a fully static version of your application. Use the next export command to create a out directory with static files, suitable for hosting on static servers.

17. How do you configure Webpack in a Next.js project?

Customize Webpack by modifying the webpack property in next.config.js, allowing you to add custom loaders, plugins, and other configurations.

18. How do you handle forms and form validation in a Next.js application?

Use libraries like Formik or React Hook Form for form handling and Yup or other validation libraries for schema-based validation.

19. How can you handle cross-origin requests (CORS) in a Next JS application when making API requests to a different domain?

To enable CORS, configure the server or API endpoint receiving your requests. CORS headers may need to be established to permit requests from the domain of your Next.js application. Another option is utilizing serverless functions as proxy endpoints to manage CORS headers effectively.

20. Describe scenarios where you would choose to use getStaticProps over getServerSideProps, and vice versa.

Choosing between getStaticProps and getServerSideProps depends on several factors in your Next.js application. Here’s a breakdown of scenarios where each method shines:

Choose getStaticProps when:

• Content is static and rarely changes: Pre-rendering pages at build time with getStaticProps delivers lightning-fast performance and optimal SEO, as search engines can readily crawl and index the content.
• Scalability and cost-effectiveness: Since page generation happens at build time, no server requests are needed on every visit, improving server performance and reducing costs.
• Improved user experience: Pages load instantly as they’re already pre-rendered, leading to a smooth and responsive user experience, especially for initial visits.

Choose getServerSideProps when:

• Dynamic content that frequently updates: Use getServerSideProps to fetch data and pre-render pages at request time when content changes frequently, like news articles, stock prices, or personalized user data.
• User authentication and personalization: Access user-specific data like shopping carts or logged-in states, personalize UI elements, and implement authentication logic dynamically based on user requests.
• API data integration: For real-time data from external APIs or databases, getServerSideProps allows fetching and integrating data directly into page responses during server-side rendering.

21. Explain the purpose of the next export command. When would you use it, and what are its limitations?

In the next version of Next.js, 12.2, the next export command has become deprecated and removed in favor of configuring static exports within next.config.js. However, understanding its previous purpose and limitations can still be relevant for older projects or migrating to the new approach.

Purpose:

• next export used to generate a static version of your Next.js application, meaning all pages and their corresponding HTML, CSS, and JavaScript files were pre-rendered and saved to a static folder (/out).
• This static directory could then be hosted on any web server that serves static assets, eliminating the need for a Node.js server to run Next.js at runtime.

Use cases:

• Offering faster deployment times and lower server costs compared to server-side rendering.
• Improved search engine optimization (SEO)
• Faster initial page load

Limitations:

• Dynamic content limitations
• Higher build times
• Limited flexibility

Current approach:

With the next export command gone, static site generation is now configured within the next.config.js file through the output: export option. This option offers more flexibility and control over static exports, allowing you to fine-tune which pages or routes to pre-render and define custom configurations.

22. How do you implement middleware in a Next.js application?

Middleware can be implemented using API routes, custom server logic, or integrating libraries like next-connect for handling middleware in API routes.

23. How do you optimize the performance of a Next.js application?

Optimized Next.js application with code splitting, lazy loading, image optimization, server-side caching, and CDN caching. You could also run performance monitoring using profiling tools like Lighthouse or WebPageTest to find places for improvement.

24. How do you handle data fetching from multiple sources in a single Next.js page?

Use Promise.all in getStaticProps or getServerSideProps to fetch data from multiple sources concurrently. Aggregate the data and pass it as props to the page component for rendering.

25. How would you set up Next.js to work with GraphQL, and what are some of the advantages?

Configure Next.js with GraphQL by setting up a GraphQL client, defining GraphQL queries and mutations, and using these hooks, such as useQuery and useMutation, in your components. All this brings about target advantages: it fetches data efficiently, has strong typing with TypeScript, and is able to fetch only that data that is required.

Conclusion

Next.js is a very important package to be mastered by any developer aspiring to greatness in modern web development. This set of questions thus guides in the preparation for every bit concerning Next.js, from the simplest understanding to the most advanced application. Take some time to get familiar with these questions and their answers, and you are set to ensure confidence in your Next.js interview. Keep learning. Stay updated on the most recent trends and new ways of practicing Next.js to stay relevant as demand increases in job pipelines.

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