Next.js interview questions asked in FANG companies with solutions

-

 Here are Next.js interview questions that are typically asked by FANG (Facebook, Amazon, Netflix, Google) companies, along with detailed answers and solutions. These questions focus on advanced concepts such as optimization, architecture, SSR/SSG, performance, and scalability — topics that are crucial for large-scale applications, which FANG companies prioritize.

1. What is the difference between Static Site Generation (SSG) and Server-Side Rendering (SSR) in Next.js?

Answer:

  • SSG (Static Site Generation): Pages are pre-rendered at build time. This is suitable for content that doesn’t change frequently (like blog posts, marketing pages, etc.). It provides the best performance because pages are served as static HTML.

  • SSR (Server-Side Rendering): Pages are rendered on the server for each request. SSR is useful when the content is dynamic and needs to be updated on every request (e.g., user profiles, live data). This is slower than SSG but provides fresh data on every request.

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

2. How does Next.js handle code splitting, and why is it beneficial for performance?

Answer:
Next.js automatically splits your JavaScript code into smaller chunks based on the pages that need them. This is done using dynamic imports and Webpack, ensuring that only the necessary code for each page is loaded. Code splitting helps improve performance by reducing the initial JavaScript payload, especially in large applications.

For example, each page in a Next.js app will only load its associated JavaScript bundle, not the entire app, which can reduce the page load time significantly.

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

Answer:
Incremental Static Regeneration (ISR) is a feature that allows you to update static pages after the application has been deployed without needing to rebuild the entire site. ISR combines the benefits of SSG with the flexibility of updating pages at runtime.

With ISR, you can set a revalidation time for your static pages. Once the revalidation time passes, Next.js will regenerate the page in the background for subsequent requests while serving the stale page to the user.

Example:

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

4. How do you optimize performance in Next.js?

Answer:
Next.js provides several built-in features for performance optimization:

  • Automatic Code Splitting: Next.js automatically splits your JavaScript code based on routes, so only the necessary code is loaded for the current page.
  • Image Optimization: The next/image component optimizes images by serving them in modern formats like WebP and automatically resizing them.
  • Static Site Generation (SSG): Pre-render pages at build time, improving performance for static content.
  • Server-Side Rendering (SSR): Dynamically render pages on the server when necessary.
  • Prefetching: Next.js automatically prefetches pages linked with the Link component when they are visible in the viewport.
  • Lazy Loading: Use next/dynamic to lazy load React components only when needed.

Example (dynamic import):

js
import dynamic from 'next/dynamic';

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

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

5. How do you handle dynamic routing in Next.js?

Answer:
Next.js uses file-based routing. To create a dynamic route, use square brackets ([ ]) to define parameters in the file name.

For example:

  • pages/[id].js will match /1, /2, etc., where id is a dynamic parameter.

To access the parameter value inside the component, you can use the useRouter hook from next/router.

js
import { useRouter } from 'next/router';

function Post() {
  const router = useRouter();
  const { id } = router.query;
  return <div>Post ID: {id}</div>;
}

6. What is the role of getServerSideProps in Next.js?

Answer:
getServerSideProps is used for server-side rendering (SSR). This function runs on the server for every request and fetches data before rendering the page. It's ideal when you need to fetch data that changes frequently or depends on the request context (e.g., user authentication).

Example:

js
export async function getServerSideProps(context) {
  const res = await fetch(`https://api.example.com/data?id=${context.params.id}`);
  const data = await res.json();
  return { props: { data } };
}
  • This will fetch data on every request and render the page with up-to-date information.

7. Explain how getStaticProps and getServerSideProps differ in terms of performance and use cases.

Answer:

  • getStaticProps: Runs at build time and is used for Static Site Generation (SSG). It's ideal for pages where the data does not change frequently (e.g., blog posts). The page is pre-rendered, which provides the best performance and SEO.

  • getServerSideProps: Runs at request time and is used for Server-Side Rendering (SSR). It's used for pages that require fresh data on each request (e.g., user dashboards, dynamic data).

Performance:

  • getStaticProps is faster because the page is already generated at build time.
  • getServerSideProps can be slower since it requires fetching data on each request.

8. How do you manage global state in Next.js?

Answer:
Global state in Next.js can be managed using any state management library like Redux, React Context API, MobX, or even Apollo Client (for GraphQL).

  • React Context API: The Context API can be used to pass data globally across components without needing to prop drill.

Example (React Context API):

js
// context.js
import React, { createContext, useState, useContext } from 'react';

const GlobalContext = createContext();

export function GlobalProvider({ children }) {
  const [user, setUser] = useState(null);

  return (
    <GlobalContext.Provider value={{ user, setUser }}>
      {children}
    </GlobalContext.Provider>
  );
}

export function useGlobalContext() {
  return useContext(GlobalContext);
}

// _app.js
import { GlobalProvider } from '../context';

function MyApp({ Component, pageProps }) {
  return (
    <GlobalProvider>
      <Component {...pageProps} />
    </GlobalProvider>
  );
}

export default MyApp;

9. What is next/image and how does it improve performance?

Answer:
next/image is an optimized image component in Next.js that automatically handles image resizing, lazy loading, and serving images in modern formats like WebP. It reduces the image file size, improves load time, and increases performance.

Example usage:

js
import Image from 'next/image';

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

This ensures:

  • Automatic resizing for different screen sizes.
  • Lazy loading of images when they come into the viewport.
  • Image format conversion (e.g., to WebP) for optimized delivery.

10. How does Next.js handle environment variables?

Answer:
Next.js allows you to use environment variables to manage configuration settings such as API keys, environment-specific settings, etc.

  • Use .env.local for local development.
  • Use .env.production for production-specific settings.

To access environment variables in the client-side code, prefix them with NEXT_PUBLIC_. For server-side variables, you can access them directly.

Example:

js
// .env.local
NEXT_PUBLIC_API_URL='https://api.example.com'

You can access the variable in the code like this:

js
const apiUrl = process.env.NEXT_PUBLIC_API_URL;

For server-side access:

js
const dbUrl = process.env.DB_URL; // Without NEXT_PUBLIC_ prefix

11. How does Next.js optimize and pre-fetch pages?

Answer:
Next.js automatically pre-fetches pages linked with the Link component when they come into the viewport. This helps in reducing navigation latency and providing an instant user experience.

Example of pre-fetching:

js
import Link from 'next/link';

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

Next.js will automatically prefetch the /about page in the background when the link comes into view, so navigating to it will be instantaneous.

12. What is next/head and how do you use it for SEO?

Answer:
next/head allows you to modify the <head> section of your pages, which is crucial for SEO. You can add custom meta tags, titles, and other SEO-related tags dynamically.

Example:

js
import Head from 'next/head';

function HomePage() {
  return (
    <div>
      <Head>
        <title>My Awesome Page</title>
        <meta name="description" content="This is my awesome page" />
      </Head>
      <h1>Welcome to my awesome page!</h1>
    </div>
  );
}

By customizing <head>, you can control important SEO factors like title, description, OG tags, etc.

These questions are a mix of basic, advanced, and practical Next.js topics, reflecting the complexity and high expectations in FANG interviews. Focusing on performance optimization, static/dynamic rendering, and best practices will help you succeed in these interviews.

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