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Interviews / Frontend Engineering / Your Next.js application is slow. How do you optimize its performance?

Questions

What is the difference between server-side rendering (SSR) and static site generation (SSG) in Next.js?
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What is the `_app.js` file and what is it used for in Next.js?
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What is the `_document.js` file and what is it used for in Next.js?
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How do you do data fetching in Next.js?
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How do you do routing in Next.js?
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What are API routes and how do you use them in Next.js?
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How do you do styling in Next.js?
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Your Next.js application is slow. How do you optimize its performance?
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How do you handle authentication and authorization in Next.js?
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How do you handle environment variables in Next.js?
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How do you deploy a Next.js application?
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What is middleware and how do you use it in Next.js?
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Your Next.js application is slow. How do you optimize its performance?

debugging Performance Optimization Interactive Quiz Code Examples

The Scenario

You are a frontend engineer at an e-commerce company. You are responsible for a Next.js application that is experiencing performance issues. The application is slow to load, and it is not very responsive.

You need to find a way to optimize the performance of the application.

The Challenge

Explain your strategy for optimizing the performance of a Next.js application. What are the key areas that you would focus on, and what tools would you use to help you?

Wrong Approach

A junior engineer might not have a clear strategy for optimizing the performance of a Next.js application. They might try to solve the problem by just making random changes to the code, which would not be very effective.

Right Approach

A senior engineer would have a clear strategy for optimizing the performance of a Next.js application. They would be able to explain the key areas to focus on, and they would have a clear plan for how to use tools like the Next.js Analytics and the webpack-bundle-analyzer to identify and fix performance bottlenecks.

Step 1: Analyze the Performance of the Application

The first step is to analyze the performance of the application. We can use the Next.js Analytics to do this. The Next.js Analytics provides a number of metrics that can be used to measure the performance of the application, such as the Time to First Byte (TTFB) and the First Contentful Paint (FCP).

Step 2: The Key Areas to Focus On

AreaDescription
Bundle SizeA large bundle size can slow down the initial load time of the application.
Render PerformanceA slow render performance can make the application feel unresponsive.
Data FetchingA slow data fetching performance can delay the rendering of the page.

Step 3: Optimize the Bundle Size

Here are some techniques we can use to optimize the bundle size:

  • Code splitting: Split the code into smaller chunks that can be loaded on demand.
  • Tree shaking: Remove unused code from the bundle.
  • Lazy loading: Lazy load components and libraries to improve the initial load time.

We can use the @next/bundle-analyzer to visualize the size of the bundle and to identify any large dependencies.

Step 4: Optimize the Render Performance

Here are some techniques we can use to optimize the render performance:

  • Use React.memo to memoize functional components.
  • Use useMemo and useCallback to memoize values and functions.
  • Use next/image to optimize images.

Step 5: Optimize the Data Fetching Performance

Here are some techniques we can use to optimize the data fetching performance:

  • Use getStaticProps for pages that do not change often.
  • Use getServerSideProps for pages that have personalized data.
  • Use Incremental Static Regeneration (ISR) to re-generate static pages in the background.

Practice Question

You are building a page that displays a list of products. The list of products is the same for all users and does not change often. Which of the following would be the most appropriate?