Top 10 Next.js Interview Questions for Full Stack Developers

Next.js has rapidly become the go-to framework for building modern web applications, providing developers with both exceptional performance and a strong developer experience. For Full Stack Developers, mastering Next.js can unlock opportunities to build highly scalable and SEO-friendly web applications.

This post covers the Top 10 Next.js Interview Questions to help you prepare for technical discussions and demonstrate your expertise.

Table of Contents

1. What is the Difference Between Next.js and React?
2. SSR vs SSG vs ISR in Next.js
3. API Routes in Next.js
4. Image Optimization in Next.js
5. Dynamic Routing and Catch-All Routes
6. App Directory vs Pages Directory (Next.js 13+)
7. Server Actions and Mutations (Next.js 14+)
8. SEO in Next.js Apps
9. Deployment Strategies (Vercel, Docker)
10. Authentication with NextAuth.js
11. FAQs

1. What is the Difference Between Next.js and React?

While React is a library focused solely on building user interfaces, Next.js is a full-fledged framework built on top of React that provides a set of tools to enhance application performance, scalability, and developer productivity.

Key Differences:

• Server-Side Rendering (SSR):

Next.js provides built-in SSR capabilities, rendering pages on the server for improved SEO and faster load times. React, on its own, requires additional libraries like react-dom/server or frameworks like Next.js to enable SSR.

• File-Based Routing:

Unlike React, which requires developers to configure routes manually using React Router, Next.js uses a file-based routing system. Simply place a file in the pages/ directory, and the URL is automatically mapped to it.

• Full Stack Capabilities:

Next.js includes support for API routes, turning the framework into a complete full stack solution. React alone doesn’t provide backend capabilities.

Example:

A React setup requires routing and state management libraries like React Router and Redux, whereas Next.js simplifies these with built-in solutions.

2. SSR vs SSG vs ISR in Next.js

Next.js provides developers with three main rendering strategies, each suited for specific use cases.

Server-Side Rendering (SSR)

Pages are generated dynamically on each request:

• Pros: Ensures up-to-date content and works well with user-specific data.
• Use Case: Dashboards or admin pages.
• Example Code:

   export async function getServerSideProps() {
     const data = await fetchData();
     return { props: { data } };
   }

   export async function getServerSideProps() {
     const data = await fetchData();
     return { props: { data } };
   }

Static Site Generation (SSG)

Pages are pre-rendered at build time:

• Pros: Extremely fast as pages are cached and served as static files.
• Use Case: Marketing pages or blogs.
• Example Code:

   export async function getStaticProps() {
     const posts = await fetchPosts();
     return { props: { posts } };
   }

   export async function getStaticProps() {
     const posts = await fetchPosts();
     return { props: { posts } };
   }

Incremental Static Regeneration (ISR)

A hybrid approach that updates static pages at regular intervals.

• Pros: Combines the performance of SSG with fresh content updates.
• Use Case: E-commerce product pages.
• Example Code:

   export async function getStaticProps() {
     return { props: {}, revalidate: 10 };
   }

   export async function getStaticProps() {
     return { props: {}, revalidate: 10 };
   }

3. API Routes in Next.js

API routes allow you to build backend functionality directly in Next.js without relying on external servers.

Example:

1. Create an API endpoint in the pages/api directory:

   export default function handler(req, res) {
     res.status(200).json({ message: 'Hello from Next.js API route!' });
   }

   export default function handler(req, res) {
     res.status(200).json({ message: 'Hello from Next.js API route!' });
   }

2. Access the API via /api/hello.

Use Case: Build custom endpoints for authentication, handling forms, or fetching third-party data.

4. Image Optimization in Next.js

Next.js provides a built-in <Image> component to optimize images automatically for performance and responsiveness.

Key Features:

• Lazy Loading: Loads images only when visible on the viewport.
• Automatic Resizing: Serves appropriately sized images for different screen resolutions.

Example Code:

   import Image from 'next/image';

   function HomePage() {
     return <Image src="/example.jpg" width={600} height={400} alt="Example Image" />;
   }

   import Image from 'next/image';

   function HomePage() {
     return <Image src="/example.jpg" width={600} height={400} alt="Example Image" />;
   }

Pro Tip: Use the loader property to integrate external image hosting services.

5. Dynamic Routing and Catch-All Routes

Next.js supports dynamic and catch-all routing via square brackets in file names.

Dynamic Routes:

Create pages/product/[id].js for product details by ID.

Example URL pattern: /product/123

Catch-All Routes:

Create pages/docs/[...slug].js for nested routes.

Example URL patterns:

• /docs/getting-started
• /docs/api/introduction

Use Case: Build dynamic pages for blogs, products, or documentation.

6. App Directory vs Pages Directory (Next.js 13+)

Pages Directory

• Legacy routing system.
• Includes getServerSideProps, getStaticProps.

App Directory

Introduced in Next.js 13 with React Server Components:

• Enables app/ architecture for improved server-rendering efficiency.
• Modular layouts and parallel data fetching.

Best Practice: Use app/ for new projects, as it’s the default in Next.js 13+.

7. Server Actions and Mutations (Next.js 14+)

Server Actions allow developers to handle server-side mutations directly in React components.

Example:

   'use server';

   async function updateData(formData) {
     // Mutate server-side data
   }

   'use server';

   async function updateData(formData) {
     // Mutate server-side data
   }

Use Case: Simplify mutation handling for use cases like form submissions.

8. SEO in Next.js Apps

SEO Features:

• Meta Tags: Set <title> and <meta> tags dynamically using the Head component.

   import Head from 'next/head';
   function Page() {
     return (
       <Head>
         <title>My SEO Page</title>
         <meta name="description" content="This is an SEO-optimized page." />
       </Head>
     );
   }

   import Head from 'next/head';
   function Page() {
     return (
       <Head>
         <title>My SEO Page</title>
         <meta name="description" content="This is an SEO-optimized page." />
       </Head>
     );
   }

• Performance Optimizations: Built-in image optimization and static generation improve Core Web Vitals.

9. Deployment Strategies (Vercel, Docker)

Vercel:

The official hosting platform for Next.js, offering serverless deployment with built-in CI/CD.

Docker:

Deploy Next.js applications in containerized environments for scalability.

Example Dockerfile:

   FROM node:16
   COPY . .
   RUN npm install
   RUN npm run build
   CMD ["npm", "start"]

   FROM node:16
   COPY . .
   RUN npm install
   RUN npm run build
   CMD ["npm", "start"]

10. Authentication with NextAuth.js

Next.js apps can use NextAuth.js for fully managed authentication.

Example:

1. Install the package:

   npm install next-auth

   npm install next-auth

2. Create /pages/api/auth/[...nextauth].js:

   import NextAuth from 'next-auth';
   import Providers from 'next-auth/providers';

   export default NextAuth({
     providers: [
       Providers.Google({
         clientId: process.env.GOOGLE_CLIENT_ID,
         clientSecret: process.env.GOOGLE_CLIENT_SECRET
       })
     ]
   });

   import NextAuth from 'next-auth';
   import Providers from 'next-auth/providers';

   export default NextAuth({
     providers: [
       Providers.Google({
         clientId: process.env.GOOGLE_CLIENT_ID,
         clientSecret: process.env.GOOGLE_CLIENT_SECRET
       })
     ]
   });

Use Case: Add login functionality for social and email authentication.

FAQs

Does Next.js work only with React?

Yes, Next.js is a framework specifically built on top of React.

What makes ISR better than traditional SSG or SSR?

ISR combines speed with flexibility by updating static pages at runtime without rebuilding the app.

Can I deploy a Next.js app without Vercel?

Yes, Next.js apps can also be deployed with Docker, AWS, Render, or other server hosting platforms.

Summary

Next.js empowers Full Stack Developers by providing cutting-edge features like server-side rendering, API routing, and automated image optimization. Whether you’re troubleshooting Catch-All Routes or optimizing performance with static generation, understanding these core concepts will undoubtedly boost your expertise.

Prepare for your next technical interview with these common Next.js questions, and experiment with its innovative features to stay ahead in web development!