Next.js is a popular framework for building web applications with React. It offers many features that make development easier and faster, such as server-side rendering, code splitting, routing, and more. In this article, we will explore some of the most common Next.js interview questions and how to answer them. Whether you are a beginner or a senior developer, these questions will help you prepare for your next Next.js job interview.


1. What is Next.js?

Next.js is a React framework developed by Vercel. It enables features such as server-side rendering and generating static websites for React-based web applications.

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

Next.js offers features like server-side rendering, static site generation, automatic code splitting, file-system based routing, and built-in CSS and Sass support.

3. How does Server Side Rendering (SSR) work in Next.js?

In Next.js, any file inside the `pages` directory will be treated as a page. If you export an async function called `getServerSideProps` from a page, Next.js will pre-render this page on each request using the data returned by `getServerSideProps`.

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

Static Site Generation is the process of rendering a website or application at build time, resulting in static HTML, CSS, and JavaScript files. In Next.js, by exporting an async function called `getStaticProps` from a page, you can generate a static page.

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

ISR allows you to create a static page at build time but update it incrementally at runtime as traffic comes in, ensuring that your users always see the most up-to-date information.

6. How does file-system routing work in Next.js?

In Next.js, the file system is the main API. Every `.js` file becomes a route that gets automatically processed and rendered.

7. How do you create dynamic routes in Next.js?

Dynamic routes can be created in Next.js by adding brackets `[]` to a page `[].js` inside the `pages` directory.

8. How do you handle API routes in Next.js?

API routes can be created by creating a `js` file inside the `pages/api` directory. These will be server-side routes and won't be accessible on the client side.

9. How do you handle CSS in Next.js?

Next.js has built-in support for CSS and Sass which allows you to import `.css` and `.scss` files. Using `styled-jsx` for CSS-in-JS styling is also supported out of the box.

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

You can use environment variables in Next.js by creating a `.env.local` file in the root directory and prefixing the variable with `NEXT_PUBLIC_` to expose it to the browser.


11. How do you handle error pages in Next.js?

You can create a custom error page by creating a `_error.js` file inside `pages` directory.

12. What is `next/link` in Next.js?

`next/link` is a component built-in to Next.js for enabling client-side transitions between routes.

13. How do you prefetch pages in Next.js?

In Next.js, all `` tags automatically prefetch pages in the background.

14. What is `next/image` in Next.js?

`next/image` is a component built-in to Next.js for optimizing images.

15. How do you deploy a Next.js application?

Next.js can be deployed on any hosting provider that supports Node.js. However, the easiest way to deploy Next.js is to use the Vercel platform developed by the creators of Next.js.

16. How do you use middleware in Next.js?

Middleware in Next.js allows you to run code before your request is completed. You can use it for tasks like manipulating the request/response objects and handling session authentication.

17. How do you use Next.js with TypeScript?

To start a new Next.js project with TypeScript, run `npx create-next-app@latest --typescript`. To add TypeScript to an existing Next.js project, add a `tsconfig.json` file to your project and run `npm install --save typescript @types/react @types/node`.

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

Next.js provides several ways to optimize performance, including automatic code splitting, prefetching, image optimization with `next/image`, and more.

19. How do you handle authentication in Next.js?

Authentication in Next.js can be handled in various ways, including traditional session authentication, JWT authentication, and third-party OAuth.

20. How do you test Next.js applications?

Next.js can be tested using any JavaScript testing framework. Jest and React Testing Library are often used for unit and integration tests, while Cypress can be used for end-to-end tests.

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