Next.js top 50 interview question answer with solutions in details

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 Here are 50 commonly asked Next.js interview questions with detailed answers. These questions cover a wide range of topics including routing, data fetching, server-side rendering (SSR), static site generation (SSG), and more.

1. What is Next.js?

Answer:
Next.js is a React framework used for building static and server-rendered web applications. It provides features like server-side rendering (SSR), static site generation (SSG), and API routes out of the box. Next.js simplifies the development of production-ready React applications by handling complex configurations and optimizations automatically.

2. What are the key features of Next.js?

Answer:

  • Server-Side Rendering (SSR): Pages are rendered on the server for SEO benefits.
  • Static Site Generation (SSG): Pre-render pages at build time.
  • API Routes: Backend API logic within the same project using simple files.
  • Automatic Code Splitting: Splits the code into smaller bundles, ensuring fast loading.
  • File-based Routing: Simplifies routing with file-based routing instead of manual setup.
  • Optimized Image Handling: next/image automatically optimizes images.
  • Fast Refresh: Quick updates during development with zero configuration.
  • Pre-fetching Links: Automatically pre-fetches linked pages to improve navigation speed.

3. What is SSR (Server-Side Rendering) in Next.js?

Answer:
Server-side rendering (SSR) is a rendering method where HTML is generated on the server for each request. In Next.js, pages can be pre-rendered on the server for each incoming request, making it SEO-friendly and improving load times. You can implement SSR using the getServerSideProps function.

Example:

export async function getServerSideProps() {
  const res = await fetch('https://api.example.com/data');
  const data = await res.json();
  return { props: { data } };
}

4. What is SSG (Static Site Generation) in Next.js?

Answer:
Static Site Generation (SSG) is a method where HTML pages are generated at build time. SSG improves performance as the page is pre-rendered and served from a CDN. In Next.js, you can use the getStaticProps function to generate static pages at build time.

Example:

export async function getStaticProps() {
  const res = await fetch('https://api.example.com/data');
  const data = await res.json();
  return { props: { data } };
}

5. What is the difference between getServerSideProps and getStaticProps?

Answer:

  • getServerSideProps: Fetches data on each request, resulting in server-side rendering (SSR). This is used when data needs to be updated frequently or cannot be fetched at build time.
  • getStaticProps: Fetches data at build time, generating static HTML. It's ideal for data that doesn’t change often (e.g., blog posts, product pages).

6. What is Incremental Static Regeneration (ISR) in Next.js?

Answer:
ISR allows you to update static content after the site has been built and deployed. With ISR, you can define the revalidate time in getStaticProps, so a page is regenerated after a set period.

Example:

export async function getStaticProps() {
  const res = await fetch('https://api.example.com/data');
  const data = await res.json();
  return {
    props: { data },
    revalidate: 60, // Revalidate every 60 seconds
  };
}

7. What is Dynamic Routing in Next.js?

Answer:
Dynamic routing in Next.js allows you to create routes that are based on data. You can create dynamic routes using brackets ([]) in the pages directory.

Example:

  • pages/[id].js will map to any route like /1, /2, etc.
  • You can access the dynamic part in your component using useRouter() or getServerSideProps.

8. How do you handle routing in Next.js?

Answer:
Routing in Next.js is based on the file system. Pages are automatically routed based on the file structure in the pages directory. Dynamic routes can be created using square brackets ([ ]).

Example:

  • A file pages/about.js would map to /about.
  • A dynamic file pages/[id].js maps to /123, /456, etc.

9. What is getStaticPaths and why is it needed?

Answer:
getStaticPaths is used alongside getStaticProps to define a list of paths to pre-render for dynamic routes. It's required when you have dynamic routes and want to generate static pages at build time.

Example:

export async function getStaticPaths() {
  const res = await fetch('https://api.example.com/posts');
  const posts = await res.json();

  const paths = posts.map(post => ({
    params: { id: post.id.toString() }
  }));

  return { paths, fallback: false };
}

10. What is the use of Link component in Next.js?

Answer:
The Link component in Next.js is used to create client-side navigation between pages. It prefetches the linked page in the background for faster navigation.

Example:

import Link from 'next/link';

function HomePage() {
  return (
    <Link href="/about">
      <a>Go to About</a>
    </Link>
  );
}

11. What is the useRouter hook in Next.js?

Answer:
useRouter is a hook provided by Next.js that allows you to access the router object and get information about the current route, such as query parameters, pathname, etc.

Example:

import { useRouter } from 'next/router';

function MyComponent() {
  const router = useRouter();
  const { id } = router.query;

  return <div>Post ID: {id}</div>;
}

12. How do you optimize images in Next.js?

Answer:
Next.js provides the next/image component for automatic image optimization. It supports features like lazy loading, resizing, and serving images in the WebP format.

Example:

import Image from 'next/image';

function MyPage() {
  return (
    <Image
      src="/path/to/image.jpg"
      alt="Example image"
      width={500}
      height={300}
    />
  );
}

13. What is API Routes in Next.js?

Answer:
API routes in Next.js allow you to define backend API endpoints within your Next.js application. You can create API routes by adding JavaScript or TypeScript files inside the pages/api directory.

Example:

// pages/api/hello.js
export default function handler(req, res) {
  res.status(200).json({ message: 'Hello World' });
}

14. How can you deploy a Next.js application?

Answer:
You can deploy a Next.js app on several platforms:

  • Vercel: The platform from the creators of Next.js. It offers seamless deployment and optimizations for Next.js apps.
  • Netlify: Also supports Next.js deployment.
  • AWS, Heroku, or DigitalOcean: You can deploy on these cloud platforms using Docker or Node.js.

Vercel is the easiest option for deploying Next.js projects. You can deploy directly from GitHub, GitLab, or Bitbucket.

15. How does Next.js handle CSS and CSS-in-JS?

Answer:
Next.js supports multiple ways of styling:

  • CSS Modules: Scoped CSS for components.
  • Global CSS: Include global styles in _app.js.
  • CSS-in-JS: You can use libraries like styled-components or @emotion/react.

Example (CSS Module):

import styles from './button.module.css';

function Button() {
  return <button className={styles.btn}>Click me</button>;
}

16. What are the advantages of using Next.js over React alone?

Answer:

  • SEO-friendly: Automatic SSR and SSG make Next.js more SEO-friendly than traditional client-side React apps.
  • Optimized performance: Built-in features like image optimization and automatic code splitting improve performance.
  • Easy deployment: Platforms like Vercel offer seamless deployment for Next.js apps.
  • Hybrid rendering: Next.js allows you to mix SSR, SSG, and client-side rendering in one app.

17. What is next.config.js in Next.js?

Answer:
next.config.js is the configuration file in Next.js where you can define custom settings such as environment variables, Webpack configurations, redirects, and rewrites.

Example:

module.exports = {
  env: {
    customKey: 'my-value',
  },
  webpack: (config, { isServer }) => {
    if (!isServer) {
      config.node = { fs: 'empty' };
    }
    return config;
  },
};

18. What is the difference between getStaticProps and getServerSideProps?
Answer:
  • getStaticProps: Fetches data at build time and generates a static page (SSG).
  • getServerSideProps: Fetches data on every request and renders a new page on the server (SSR).
19. What are "fallback" pages in Next.js?
Answer:
Fallback pages in Next.js are used when getStaticPaths is used with getStaticProps. When fallback is set to true, Next.js will serve a static page while new paths are being generated.
20. How do you handle dynamic imports in Next.js?
Answer:
You can use next/dynamic to dynamically import React components, which can improve performance by splitting the code.
Example:
import dynamic from 'next/dynamic';

const DynamicComponent = dynamic(() => import('../components/DynamicComponent'));

function MyPage() {
  return <DynamicComponent />;
}

21. What is getInitialProps in Next.js?
Answer:
getInitialProps is an older method for fetching data before rendering a page. It’s less commonly used now as getServerSideProps and getStaticProps are preferred.
22. How can you manage authentication in Next.js?
Answer:
You can manage authentication in Next.js using tools like JWT (JSON Web Tokens), NextAuth.js, or Auth0. These tools help with login, session management, and protecting pages from unauthorized access.
23. What are the routing patterns in Next.js?
Answer:
  • Static Routes: Direct mappings to files in the pages directory.
  • Dynamic Routes: Use [param] to handle routes with dynamic parameters.
  • Catch-all Routes: Use [...param] to match multiple parameters.
24. How do you handle environment variables in Next.js?
Answer:
You can manage environment variables in Next.js by adding them to .env.local or next.config.js. To use them in the app, prefix them with NEXT_PUBLIC_ for client-side access.
Example:
// .env.local
NEXT_PUBLIC_API_URL='https://api.example.com'

25. How do you prefetch pages in Next.js?
Answer:
Next.js automatically prefetches linked pages using the Link component when they are visible in the viewport, improving navigation speed.
26. What is the file-based routing system in Next.js?
Answer:
Next.js uses file-based routing where the structure of your files in the pages directory corresponds to the routes in the application. Each file in pages/ becomes a route.
27. What is the default behavior for rendering in Next.js?
Answer:
By default, Next.js will statically render a page if getStaticProps is used, and it will render a page on the server if getServerSideProps is used.
28. How do you create a custom Document (_document.js) in Next.js?
Answer:
To customize the default HTML document structure in Next.js (e.g., adding custom <head> tags), you can create a custom _document.js file.
Example:
// pages/_document.js
import Document, { Html, Head, Main, NextScript } from 'next/document';

class MyDocument extends Document {
  render() {
    return (
      <Html>
        <Head />
        <body>
          <Main />
          <NextScript />
        </body>
      </Html>
    );
  }
}

export default MyDocument;

29. What is the useEffect hook in Next.js?
Answer:
useEffect is a React hook that allows you to perform side effects in function components. It is often used for tasks like data fetching, subscriptions, or manually changing the DOM.
30. How do you optimize performance in Next.js?
Answer:
  • Code Splitting: Next.js automatically splits your code, so only necessary parts are loaded.
  • Image Optimization: Use the next/image component.
  • Lazy Loading: Use next/dynamic to dynamically import components.
  • Static Site Generation (SSG): Pre-render content at build time.
31. What is the next/image component?
Answer:
The next/image component is an optimized image component built into Next.js. It automatically optimizes images for size, format, and delivery.
32. How do you handle 404 pages in Next.js?
Answer:
You can create a custom 404.js page in the pages directory, which will automatically be displayed when a user navigates to a non-existent route.
33. How do you use TypeScript with Next.js?
Answer:
Next.js has built-in support for TypeScript. To use TypeScript, simply create a tsconfig.json file in your project’s root directory, and Next.js will automatically configure it.
34. How can you deploy a Next.js app to Vercel?
Answer:
You can deploy a Next.js app to Vercel by connecting your GitHub or GitLab repository to Vercel. Vercel will automatically detect Next.js and configure everything for you.
35. What is the next/head component?
Answer:
The next/head component allows you to manage the <head> of your HTML document, including adding meta tags, title, and other elements dynamically.
36. How does Next.js handle static assets?
Answer:
Next.js serves static assets from the public/ directory. You can place images, fonts, and other static files in the public folder, and reference them with a relative URL starting from /.
37. How does Next.js handle URL rewriting?
Answer:
Next.js allows URL rewriting through next.config.js. You can define custom URL patterns for redirects and rewrites.
38. What is the getInitialProps function in Next.js?
Answer:
getInitialProps was a data-fetching method used to fetch data before the page loads. It is now replaced by getServerSideProps and getStaticProps in newer versions of Next.js.
39. How do you handle multiple layouts in Next.js?
Answer:
You can handle multiple layouts by wrapping different pages in different layout components. You can use React context to dynamically change layouts.
40. How do you set up global styles in Next.js?
Answer:
You can add global styles in the pages/_app.js file by importing the global CSS file.
Example:
import '../styles/global.css';

41. How does Next.js handle code splitting?
Answer:
Next.js automatically splits the code into smaller bundles, loading only the required code for each page.
42. How do you manage SEO in Next.js?
Answer:
You can manage SEO by using the next/head component to add meta tags, titles, and other SEO elements. Next.js also supports server-side rendering, which is crucial for SEO.
43. How do you handle forms in Next.js?
Answer:
Forms in Next.js can be handled like in any React application. You can use useState for form fields and onSubmit to handle form submission.
44. How do you implement error boundaries in Next.js?
Answer:
You can implement error boundaries in Next.js by using React’s componentDidCatch lifecycle method or the ErrorBoundary component.
45. How do you handle cookies in Next.js?
Answer:
Cookies can be managed in Next.js using libraries like js-cookie or using the cookie package for server-side handling.
46. How do you add analytics (like Google Analytics) in Next.js?
Answer:
You can add Google Analytics by adding the tracking script in the pages/_document.js file or using a third-party package like next-analytics.
47. How do you pre-fetch links in Next.js?
Answer:
Next.js automatically pre-fetches linked pages using the Link component when they are in the viewport, but you can also manually trigger pre-fetching with next/link.
48. What is getStaticProps in a dynamic route?
Answer:
You can use getStaticProps in dynamic routes along with getStaticPaths to generate static pages for dynamic content at build time.
49. What is the fallback property in getStaticPaths?
Answer:
The fallback property controls the behavior when a requested path is not pre-rendered. It can be:
  • false: Returns a 404 for missing paths.
  • true: Shows a static page while generating the missing page in the background.
  • blocking: Waits for the page to be generated before serving.
50. How do you integrate a database in Next.js?
Answer:
You can integrate a database (e.g., MongoDB, PostgreSQL) with Next.js via API routes. The API routes will handle requests to the database, and you can use libraries like mongoose, pg, or mysql2.

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