Introduction:

In the rapidly evolving landscape of web development, Next.js application has emerged as a leading framework for crafting dynamic, server-rendered React applications. At its core, Next.js application is a minimalistic framework that enables developers to build fast web applications with features like server-side rendering (SSR), static site generation (SSG), and file-system-based routing. It streamlines the development process, allowing for rapid prototyping and deployment of feature-rich web applications.

However, as applications scale and complexity increase, build times can become sluggish, affecting both developer productivity and user experience. This blog post will delve into the intricacies of optimizing a slow Next.js application, focusing on strategies to reduce build time and enhance performance. Whether you’re a seasoned developer or just beginning your journey with Next.js, you’ll find valuable insights to help you navigate the challenges of scaling your web applications efficiently.

This blog will explore the practical strategies to optimize performance and deployments in Next.js projects, including caching strategies, reducing build sizes, and troubleshooting common deployment issues.
Also read our other blog: Effortlessly Set Up Automatic SSL Certificate Renewal with Certbot on AWS EC2 (Step-by-Step Guide)

Steps Of Optimizing a slow Next.js Application to reduce build time:

1. Analyze Performance Bottlenecks

Before diving into optimizations, it’s essential to first identify where the performance issues are happening in your Next.js application. By analyzing the performance, you can pinpoint slow areas and prioritize the right optimizations. Here are some tools you can use to analyze your application’s performance:

• Lighthouse: Run a Lighthouse Audit in Chrome DevTools

Lighthouse is an open-source tool, developed by Chrome, that helps web developers assess and improve the quality of their websites. The tool runs an audit on different aspects of a web page and provides scores in the following categories:

1. Performance
Performance measures how quickly a web page loads and becomes interactive. A high performance score indicates that the page loads quickly and provides a smooth, responsive experience for users. Factors that influence performance include page load time, responsiveness, and how well resources like images, scripts, and CSS are optimized.

2. Progressive Web App (PWA)
A Progressive Web App score reflects how well the web page functions as a PWA. PWAs behave like native mobile apps, allowing them to load instantly, work offline, and be installed on a user’s device. A high score in this category means the page is optimized to provide a seamless, app-like experience, including features like offline support and fast loading times.

3. Accessibility
The accessibility score evaluates how accessible the web page is to users with disabilities. This includes considerations like text readability, color contrast, and screen reader compatibility. A higher score means the page is easier to navigate for people with various disabilities, improving inclusivity.

4. Best Practices
The best practices score assesses whether the web page follows industry standards for security, reliability, and general web best practices. This includes things like using HTTPS for secure connections, avoiding deprecated features, and ensuring the site functions correctly across different devices. A higher score means the site adheres to the latest security and usability standards.

5. SEO (Search Engine Optimization)
The SEO score indicates how well the web page is optimized for search engines. A high SEO score means the page follows best practices for search engine ranking, such as proper use of meta tags, structured data, and content optimization. This helps the page rank better on search engines like Google, making it easier for users to find.

How to use it? You can run a Lighthouse audit directly in Chrome DevTools:
1. Open Chrome DevTools.
2. Go to the “Lighthouse” tab.
3. Choose the relevant categories (Performance, Accessibility, SEO, etc.).
4. Click on Generate Report.

What can you learn?
Lighthouse will provide an overall performance score, along with suggestions for improvements. It breaks down your page’s performance in metrics like First Contentful Paint (FCP), Time to Interactive (TTI), and Largest Contentful Paint (LCP). By focusing on the areas where you receive low scores, you can prioritize what to optimize first.

• Next.js Analytics: Monitor Page Load Times and Identify Slow Pages

Next.js application offers built-in analytics that allow you to monitor page load times, performance, and identify which pages are performing poorly. It’s a great way to track your application’s overall performance.

How to use it?
1. Enable Next.js analytics by adding the next/analytics package.
2. After deploying, use Vercel or your hosting platform’s dashboard to get real-time analytics.
3. View metrics like Page Load Time, Time to First Byte (TTFB), and Total Load Time for each page.

What can you learn?
Next.js analytics helps you understand which pages are taking the longest to load. With this information, you can zoom in on problem areas and optimize them accordingly, whether that involves reducing large dependencies or optimizing server-side rendering.

• React DevTools: Profile your React components to identify re-renders and inefficient rendering logic.

React DevTools is a browser extension that provides a set of tools for debugging and profiling your React applications. It’s a profile of your React components to identify re-renders and inefficient rendering logic. The profiling feature helps you track re-renders, and detect inefficient rendering logic.

How to use it?
1. Install React DevTools extension for Chrome or Firefox.
2. Open your app and go to the React tab in DevTools.
3. Click on Profiler and start recording.
4. Interact with your app and React DevTools will record the re-renders.

What can you learn?
The Profiler tab allows you to visualize which components are re-rendering and why. Frequent re-renders are a common bottleneck that can slow down your app. You can pinpoint unnecessary re-renders and fix them by memoizing components, using React.memo, or optimizing the state management logic.

• Webpack Bundle Analyzer: Analyze JavaScript Bundle Size

Webpack Bundle Analyzer is a tool that helps you visualize the size of your JavaScript bundle. Large bundle sizes can significantly slow down your application’s load time, especially if they contain heavy dependencies.
How to use it?
1. Install webpack-bundle-analyzer as a dev dependency:npm install –save-dev webpack-bundle-analyzer
2. Add it to your Webpack config to visualize your bundles after running the build command.
3. Once your project is built, open the analyzer to see a visual map of your JavaScript bundles.

What can you learn?
With Webpack Bundle Analyzer, you can identify which dependencies are the largest and take appropriate action, such as:

• Removing unused dependencies.
• Replacing large dependencies with smaller, more efficient ones.
• Using dynamic imports to load certain parts of your application only when needed.

---

Do: Optimize Re-renders Using React.memo

Why? Reducing unnecessary re-renders is key to improving performance, especially for large applications. React.memo can help avoid re-rendering components that have the same props.

Example:

// Do: Use React.memo to optimize unnecessary re-renders
const MyComponent = React.memo(({ data }) => {
  console.log('Rendering component');
  return <div>{data}</div>;
});

// Usage
<MyComponent data="Optimized Data" />

Explanation:
In the example above, the MyComponent will only re-render if its data prop changes. If the data prop remains the same, React will skip re-rendering the component, improving performance.

---

Don’t: Trigger Re-renders with Inline Functions or Objects

Why? Inline functions or objects in JSX can cause unnecessary re-renders, because they are treated as new references each time the component renders.
Example:

// Don't: Trigger unnecessary re-renders with inline functions or objects
const MyComponent = ({ data }) => {
  return <button onClick={() => alert(data)}>Click Me</button>;
};

Explanation:
In this example, the onClick handler is created inline, which means it’s re-created every time the component re-renders. This triggers unnecessary re-renders for child components, even if the state hasn’t changed.
Better Approach:

// Do: Use a function outside JSX to avoid unnecessary re-renders
const MyComponent = ({ data }) => {
  const handleClick = () => {
    alert(data);
  };

  return <button onClick={handleClick}>Click Me</button>;
};

Explanation:
By moving the function handleClick outside of the JSX, the component avoids re-creating the function on every render, thus preventing unnecessary re-renders.

---

2. Optimize JavaScript Bundles

Large JavaScript bundles can drastically affect the performance of your application, especially when users have slower network connections or less powerful devices. Optimizing JavaScript bundles reduces the size of the files that need to be loaded, leading to faster load times and better overall performance. Below are key strategies to optimize your JavaScript bundles:

• Code Splitting: Use Next.js’s Dynamic Imports to Lazy-Load Components Code splitting allows you to break your JavaScript code into smaller chunks that can be loaded on-demand. Instead of sending the entire application in one large bundle, code splitting ensures that only the code necessary for the current page or view is loaded initially, while the rest is loaded later when needed. This helps reduce the initial load time of your web page.

How to Implement Code Splitting in Next.js application?
Next.js application makes it easy to implement code splitting by using dynamic imports. With dynamic imports, you can lazily load components or libraries that aren’t essential for the first render, improving the speed at which the page becomes interactive.
Example:

import dynamic from 'next/dynamic';

const HeavyComponent = dynamic(() => import('../components/HeavyComponent'), {
  loading: () => <p>Loading...</p>,  // Show a loading message while the component is being loaded
});

Explanation: In the above code:

• We are using next/dynamic to dynamically import HeavyComponent. This means HeavyComponent won’t be included in the main JavaScript bundle but will be loaded only when it is required.
• The loading prop provides a fallback UI (in this case, a simple loading message) while the component is being fetched.

This reduces the size of the initial JavaScript bundle, allowing the page to load faster, while the heavy component is only loaded when it is needed by the user.

• Tree Shaking: Ensure Your Build Process Removes Unused Code Tree shaking is a technique that helps remove unused code from the final JavaScript bundle. It is an optimization that occurs during the build process, and it ensures that only the code that is actually used by your application is included in the final bundle. This can significantly reduce the size of your JavaScript files.

How to Enable Tree Shaking in Next.js application?
This application uses Webpack, which supports tree shaking out of the box. However, to make sure it works properly, you need to ensure that your build process is set up to remove unused code.
In your next.config.js file, you can enable tree shaking as follows:

module.exports = {
  webpack(config) {
    config.optimization.usedExports = true;  // Enable tree shaking
    return config;
  },
};

Explanation:

• The optimization.usedExports option tells Webpack to identify and remove unused exports during the build process. By enabling this in next.config.js, you’re ensuring that only the code that is actually used in your application will be included in the final bundle.
• Tree shaking works best when you use ES6 modules (i.e., import and export syntax), as they allow Webpack to statically analyze which parts of the code are being used and which parts are not.
• Reduce Third-Party Libraries: Minimize the Use of Large External Libraries

What is the Problem with Large Third-Party Libraries?
Third-party libraries can significantly increase your JavaScript bundle size. Many popular libraries, like moment.js or lodash, contain a large amount of code, much of which might not be necessary for your application. This increases the size of the JavaScript bundle, making your web pages slower to load.
How to Minimize the Use of Large Libraries?

• Audit Dependencies: Regularly audit your dependencies to ensure that you’re only using what you really need. Tools like webpack-bundle-analyzer can help identify large libraries in your bundle.
• Use Smaller Alternatives: If you’re only using a small part of a large library, consider using smaller, more focused alternatives. For example, if you only need date manipulation from moment.js, consider using smaller libraries like date-fns or day.js.
• Avoid Overuse of Libraries: Sometimes you may not even need a third-party library to perform a simple task. Native JavaScript can often do the job just as well.

Example:

// Don't: Import the entire lodash library
import lodash from 'lodash';

const result = lodash.cloneDeep([1, 2, 3]);

Better Approach:

// Do: Import only the required function
import cloneDeep from 'lodash/cloneDeep';

const result = cloneDeep([1, 2, 3]);

Explanation:

• Instead of importing the entire lodash library, which would increase your bundle size unnecessarily, you import only the specific function you need (cloneDeep). This keeps your bundle smaller and your app more efficient.

Optimizing your JavaScript bundles is a critical part of improving web performance. By implementing code splitting, enabling tree shaking, and reducing the use of large third-party libraries, you can significantly decrease your bundle size. This results in faster page load times and a more responsive user experience, especially on mobile devices or slower networks.

---

Do: Use Dynamic Imports to Lazy-Load Heavy Components

Why? Lazy-loading components help reduce the initial bundle size by loading non-essential parts of the application only when needed.

Example:

// Do: Use dynamic imports to lazy-load heavy components
import dynamic from 'next/dynamic';

const HeavyComponent = dynamic(() => import('../components/HeavyComponent'), {
  loading: () => <p>Loading...</p>,  // Show a loading indicator until the component is loaded
});

function MyPage() {
  return (
    <div>
      <h1>Welcome to my page</h1>
      <HeavyComponent />
    </div>
  );
}

Explanation:
In this example, the HeavyComponent is not included in the initial JavaScript bundle. Instead, it is loaded only when the component is actually needed. This reduces the initial page load time and improves overall performance.

---

Don’t: Import Large Components or Libraries Globally

Why? Importing large components or libraries globally unnecessarily increases the size of the main JavaScript bundle and can slow down the page load.
Example:

// Don't: Import a large library globally
import lodash from 'lodash';  // This will add the entire lodash library to the bundle

const MyComponent = () => {
  const result = lodash.cloneDeep({ a: 1, b: { c: 2 } });
  return <div>{JSON.stringify(result)}</div>;
};

Explanation:
By importing the entire lodash library, you’re unnecessarily increasing the bundle size. Even if you only need a small part of the library, importing the whole thing leads to bloat. Instead, import only the required functions to keep your bundles smaller.

Better Approach:

// Do: Import only the required function
import cloneDeep from 'lodash/cloneDeep';  // Only the cloneDeep function is included in the bundle

const MyComponent = () => {
  const result = cloneDeep({ a: 1, b: { c: 2 } });
  return <div>{JSON.stringify(result)}</div>;
};

---

Do: Use Tree Shaking to Remove Unused Code

Why? Tree shaking eliminates unused code, reducing the size of the final bundle.
Example:

// Do: Enable tree shaking to remove unused code in the build process
// In next.config.js
module.exports = {
  webpack(config) {
    config.optimization.usedExports = true;  // Enable tree shaking
    return config;
  },
};

Explanation:
Tree shaking will ensure that only the code that is actually used in your application will be included in the final JavaScript bundle, removing any unused code and reducing the overall bundle size.

---

Don’t: Use Unoptimized Third-Party Libraries

Why? Using large third-party libraries unnecessarily increases the size of your bundles.
Example:

// Don't: Import a large utility library when it's not necessary
import moment from 'moment';  // Large library with a lot of functionality you might not need

const MyComponent = () => {
  const currentDate = moment().format('MMMM Do YYYY');
  return <div>{currentDate}</div>;
};

Explanation:
The moment library is large and includes features you may not need. Instead, you can use a smaller alternative library or just native JavaScript methods for simple tasks.

Better Approach:

// Do: Use a smaller alternative like date-fns
import { format } from 'date-fns';

const MyComponent = () => {
  const currentDate = format(new Date(), 'MMMM dd yyyy');
  return <div>{currentDate}</div>;
};

---

3. Enable Server-Side Rendering (SSR) or Static Site Generation (SSG)

When optimizing a Next.js application, choosing the right rendering method plays a crucial role in improving performance, speed, and scalability. It provides two powerful rendering strategies: Server-Side Rendering (SSR) and Static Site Generation (SSG). Enabling these correctly helps reduce build time, improve page load speed, and enhance user experience.

Server-Side Rendering (SSR): Server-Side Rendering (SSR) means that a web page is generated dynamically on the server at the time of each request. When a user accesses a page, the server fetches data, processes it, and sends a fully rendered HTML page to the browser.

How SSR Helps in Optimization?

• Improves SEO: Since the full HTML is rendered on the server, search engines can easily index the content.
• Faster Initial Load: Unlike traditional client-side rendering, where the browser fetches JavaScript first, SSR sends a fully prepared page to the user.
• Good for Dynamic Content: Best suited for pages where content changes frequently (e.g., dashboards, personalized pages, or live updates).

How to Enable SSR in Next.js application?
To enable SSR in a Next.js application, use the getServerSideProps function inside a page component.
Example of SSR in Next.js:

js
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export async function getServerSideProps() {
  const response = await fetch('<https://api.example.com/data>');
  const data = await response.json();

  return { props: { data } };
}

export default function Page({ data }) {
  return <div>Data: {data.message}</div>;
}

Server-Side Rendering (SSR) in App Router: Fetch data on every request to ensure dynamic content updates.

export default async function Page() {
  const dynamicData = await fetch('<https://api.example.com/data>', { cache: 'no-store' });
  // Render your component with dynamicData
}  

Using these modern data-fetching strategies in Next.js 13+ improves performance and aligns with the new App Router approach.

How This Optimizes Build Time?

• Since SSR fetches data at request time, it doesn’t increase the build time like static pages do.
• Pages are dynamically generated only when needed, which helps optimize performance and resource usage.

---

Static Site Generation (SSG):
Static Site Generation (SSG) means that web pages are pre-rendered at build time and stored as static HTML files. These files are then served instantly to users without additional server processing. How SSG Helps in Optimization?

• Extremely Fast Load Times: Since pages are pre-generated, they load almost instantly from the server or CDN.
• Reduced Server Load: No processing is required on each request, improving scalability.
• Best for Static Content: Ideal for blogs, landing pages, documentation, and marketing websites where data doesn’t change frequently.

How to Enable SSG in Next.js Application?

To enable SSG, use the getStaticProps function.
Example of SSG in Next.js:

js
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export async function getStaticProps() {
  const response = await fetch('<https://api.example.com/data>');
  const data = await response.json();

  return { props: { data } };
}

export default function Page({ data }) {
  return <div>Data: {data.message}</div>;
}

How This Optimize Build Time?

• Pages are built once and served to all users, reducing server workload.
• Ideal for reducing build times in Next.js applications when frequent updates are not needed.

Static Site Generation (SSG) in App Router: Fetch data at build time and cache it indefinitely. This is ideal for pages with static content.

export default async function Page() {
  const staticData = await fetch('<https://api.example.com/data>', { cache: 'force-cache' });
  // Render your component with staticData
}  

Using these modern data-fetching strategies in Next.js 13+ improves performance and aligns with the new App Router approach.

---

Do: Use SSG for Static Content That Doesn’t Change Frequently

Why?
Static Site Generation (SSG) is ideal for pages that don’t need frequent updates because it pre-renders pages at build time, making them load faster.

Example:

// Do: Use SSG for pages with static data
export async function getStaticProps() {
  const response = await fetch('<https://api.example.com/static-data>');
  const data = await response.json();

  return {
    props: { data },
    revalidate: 60, // Regenerates the page every 60 seconds
  };
}

Explanation:

• This method pre-renders the page at build time for fast performance.
• The revalidate key allows Incremental Static Regeneration (ISR), meaning the page will update every 60 seconds without requiring a full rebuild.

---

Do: Use SSR for Pages That Require Real-Time Data

Why?
Server-Side Rendering (SSR) is best when you need fresh data on every request, such as for user-specific content or frequently updated listings.

Example:

// Do: Use SSR for dynamic, frequently updated data
export async function getServerSideProps() {
  const response = await fetch('<https://api.example.com/live-prices>');
  const data = await response.json();

  return {
    props: { data },
  };
}

Explanation:

• This ensures that users always get real-time data from the server.
• SSR is useful for dashboards, personalized content, or live pricing pages.

---

4. Optimize Images and Media

Large images and media files are common culprits for slow page loads. Image optimization involves reducing the size of an image file. Because images are one of the biggest assets weighing down your app’s performance, reducing the size of image files can improve performance. Here’s how to optimize them:
Next.js application provides an inbuilt next/image component that we can use in place of the native <img> component.

• Use Next.js Image Component: The next/image component automatically optimizes images for performance.

import Image from 'next/image';

<Image src="/example.jpg" alt="Example" width={500} height={300} />;

• Compress Images: Compress images before uploading using tools like ImageOptim or Squoosh, and prefer the WebP format instead of PNG or JPEG for better performance and reduced file size.
• Lazy Load Images: Load images only when they enter the viewport.

---

Do: Use Next.js Image Component for Optimization

Why?
The next/image component automatically optimizes images by resizing, compressing, and serving them in modern formats (like WebP) based on the user’s device.

Example (Optimized Approach):

import Image from 'next/image';

const OptimizedImage = () => {
  return (
    <Image
      src="/example.jpg"
      alt="Optimized Image"
      width={500}
      height={300}
      priority // Ensures important images load faster
    />
  );
};

export default OptimizedImage;

Explanation:

• Uses next/image for built-in optimization.
• Automatically generates responsive images.
• Prioritizes important images for faster loading.

---

Don’t: Use the Native <img> Tag Without Optimization

Why?
The native <img> tag does not provide built-in optimization, leading to slower page loads and larger file sizes.

Example (Bad Approach):

const UnoptimizedImage = () => {
  return <img src="/example.jpg" alt="Unoptimized Image" width="500" height="300" />;
};

export default UnoptimizedImage;

Problems in this approach:

• No automatic compression or resizing.
• Larger file size increases page load time.
• No lazy loading by default, which can impact performance.

---

Do: Use WebP Format for Better Compression

Why?
WebP images are significantly smaller than PNG or JPEG files while maintaining high quality, improving load times.

Example (Optimized Approach with WebP):

<Image src="/example.webp" alt="Optimized Image" width={500} height={300} />

Explanation:

• Uses WebP format for smaller file sizes.
• Reduces bandwidth usage and improves performance.

---

Don’t: Use Large PNG/JPEG Files Without Compression

Why?
PNG and JPEG images are often larger, leading to unnecessary bandwidth usage and slower loading speeds.

Example (Bad Approach – Large PNG File):

<img src="/example.png" alt="Large PNG Image" width="1000" height="600" />

Problems in this approach:

• Large image size slows down the page.
• No compression results in unnecessary data transfer.
• Not responsive to different screen sizes.

---

5. Leverage Caching

Caching improves response times and reduces bandwidth usage by serving content from a cache instead of the original source. Instead of fetching data from the original source every time, caching allows the application to serve pre-stored content, making it significantly faster. Next.js application provides built-in caching mechanisms that enhance performance, especially for returning users. Next.js application has built-in caching so pages load faster. Caching can drastically reduce load times for returning users: There are two main types of caching used in Next.js application:

1. Client-Side Caching: (Using SWR for Efficient Data Fetching)

Client-side caching stores data directly in the user’s browser or a cache layer so that subsequent requests for the same data don’t need to fetch it from the server again. This improves application speed and responsiveness. One of the best ways to implement client-side caching in Next.js application is by using the SWR (Stale-While-Revalidate) strategy.

Understanding SWR (Stale-While-Revalidate) SWR is a data-fetching library developed by Vercel (the creators of Next.js) that provides automatic caching, revalidation, and background data fetching. It allows the app to show cached (stale) data instantly while fetching the latest data in the background.

How does SWR work?

1. When a request is made, SWR first serves the cached data (if available).
2. At the same time, it sends a request to fetch updated data from the server.
3. Once the new data arrives, SWR updates the cache and re-renders the component.

This approach ensures that the user always sees fast-loading content, even if the latest data is being fetched in the background.

Example: Using SWR for Client-Side Caching

jsx
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import useSWR from 'swr';

// Function to fetch data
const fetcher = (url) => fetch(url).then((res) => res.json());

const UserProfile = () => {
  const { data, error } = useSWR('/api/user', fetcher, {
    revalidateOnFocus: true, // Refresh data when the user revisits the page
    dedupingInterval: 60000, // Avoid duplicate requests within 60 seconds
  });

  if (error) return <div>Failed to load user data</div>;
  if (!data) return <div>Loading...</div>;

  return (
    <div>
      <h2>{data.name}</h2>
      <p>Email: {data.email}</p>
    </div>
  );
};

export default UserProfile;

Explanation:

• useSWR('/api/user', fetcher) fetches data from an API.
• The cached data is shown instantly while the new data is fetched in the background.
• revalidateOnFocus: true ensures that the data is refreshed when the user revisits the page.
• dedupingInterval: 60000 prevents unnecessary API calls within 60 seconds.

2. Server-Side Caching (Using CDNs and API Response Caching)

What is Server-Side Caching?
Server-side caching involves storing precomputed data at the server level, reducing the need to regenerate it every time a request is made. It is used to Implement caching mechanisms on your server or use a CDN to cache static assets. This is useful for API responses, static files, and pre-rendered pages.

There are two primary ways to implement server-side caching in Next.js application:

1. Using a CDN (Content Delivery Network)

• CDNs store and serve static assets (images, stylesheets, JavaScript files) from locations closer to the user.
• This reduces latency and improves page load speed globally.
• Example: Using Vercel Edge Network or Cloudflare for caching static assets.

2. Caching API Responses in Next.js application

• For server-side rendering (SSR), you can cache API responses using getServerSideProps to improve performance.
• Example:

jsx
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export async function getServerSideProps() {
  const res = await fetch('<https://api.example.com/data>', { cache: 'force-cache' });
  const data = await res.json();

  return {
    props: { data },
  };
}

Explanation:

• The cache: ‘force-cache‘ directive tells Next.js application to store and serve the API response from the cache instead of fetching new data each time.
• This reduces API call frequency and speeds up server response times.

---

Do: Use SWR for Efficient Client-Side Caching

Why?
SWR (Stale-While-Revalidate) is a React library for caching, revalidating, and fetching data efficiently. It improves performance by returning cached data instantly while revalidating it in the background.
Example:

import useSWR from 'swr';

// Define a fetcher function
const fetcher = (url) => fetch(url).then((res) => res.json());

export default function Profile() {
  const { data, error } = useSWR('/api/user', fetcher);

  if (error) return <div>Failed to load</div>;
  if (!data) return <div>Loading...</div>;

  return <div>Hello, {data.name}</div>;
}

Explanation:

• The useSWR hook fetches data from /api/user.
• It first returns cached data (if available), then updates it in the background.
• This prevents unnecessary network requests and ensures a faster response for returning users.

---

Do Not: Fetch Data on Every Render Without Caching

Why?
Fetching data on every render without caching leads to unnecessary API requests, increasing load times and server strain.
Example (Bad Practice):

export default function Profile() {
  const [data, setData] = React.useState(null);
  const [loading, setLoading] = React.useState(true);

  React.useEffect(() => {
    fetch('/api/user')
      .then((res) => res.json())
      .then((data) => {
        setData(data);
        setLoading(false);
      });
  }, []);

  if (loading) return <div>Loading...</div>;

  return <div>Hello, {data.name}</div>;
}

What’s Wrong?

• This method fetches data every time the component mounts, even if the data hasn’t changed.
• It does not use any caching mechanism, making the app slower and increasing unnecessary API calls.

---

6. Optimize API Calls

1. Reduce API Requests (Batch Requests & Combine Calls)

API calls play a crucial role in fetching and displaying data in a Next.js application. However, slow API responses can negatively impact page load times, causing delays in rendering and a poor user experience. Optimizing API calls ensures that the application runs efficiently, reducing unnecessary network requests and improving speed. Below are key techniques to optimize API calls in Next.js applications: Slow API responses can delay page rendering. Optimize your API calls with these tips:

Why is this important?
Making multiple API requests separately can be inefficient and slow. Instead of sending numerous requests to retrieve different sets of data, it’s best to combine multiple API calls into a single request whenever possible.

How to do it?

• Use batch processing to group multiple API calls into one request.
• Fetch multiple data points in one API request instead of making separate requests for each piece of data.

Example: Combining Multiple API Calls into One

Not Optimized: Making separate API requests for user details and user posts.

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const user = await fetch('/api/user');
const posts = await fetch('/api/posts');

Optimized: Combining both requests into a single API call.

jsx
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const data = await fetch('/api/user-with-posts');

Explanation:

• In the optimized version, the backend API is designed to return both user details and their posts in a single response, reducing the number of requests made by the client.
• This approach minimizes network overhead and speeds up the application.

2. Use Incremental Static Regeneration (ISR) for Faster Data Updates

Why is this important?
Next.js application offers Incremental Static Regeneration (ISR), which allows developers to update static content in the background without rebuilding the entire site. This is useful when the content changes frequently but doesn’t need real-time updates for every request.

ISR provides the best of both worlds:

• Fast performance like Static Site Generation (SSG) because pages are pre-rendered.
• Up-to-date content like Server-Side Rendering (SSR) because the page regenerates in the background at specified intervals.

How to use ISR?
To enable ISR, set the revalidate property in getStaticProps().

Example: Using ISR for Blog Posts

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

  return {
    props: { data },
    revalidate: 10, // Revalidate every 10 seconds
  };
}

Explanation:

• This code fetches data from an API and stores a static version of the page.
• The page will automatically refresh every 10 seconds, so users get updated content without triggering a full site rebuild.
• ISR reduces API calls by only fetching new data when necessary, rather than making a request for every user visit.

3. Cache API Responses (Client-Side & Server-Side Caching)

Why is caching important?
Fetching fresh data from an API for every request can slow down performance. Caching API responses reduces redundant API requests, ensuring that previously fetched data is stored and reused efficiently.

A. Client-Side Caching (Using SWR)

Next.js application supports SWR (Stale-While-Revalidate), which allows fetching data once and using a cached version while revalidating it in the background.
Optimized: Using SWR for API Caching

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import useSWR from 'swr';

const fetcher = (url) => fetch(url).then((res) => res.json());

const BlogPosts = () => {
  const { data, error } = useSWR('/api/posts', fetcher, {
    revalidateOnFocus: true,
  });

  if (error) return <div>Failed to load posts</div>;
  if (!data) return <div>Loading...</div>;

  return (
    <ul>
      {data.map((post) => (
        <li key={post.id}>{post.title}</li>
      ))}
    </ul>
  );
};

export default BlogPosts;

Explanation:

• SWR serves cached data first, while fetching fresh data in the background.
• Users see the cached version instantly, improving load times.
• The revalidateOnFocus: true setting ensures the data refreshes when the user revisits the page.

B. Server-Side Caching (Caching API Responses in Next.js Server)

For server-side caching, Next.js application allows caching API responses on the backend using headers or a CDN.
Optimized: Caching API Responses in getServerSideProps()

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export async function getServerSideProps() {
  const res = await fetch('<https://api.example.com/data>', {
    cache: 'force-cache', // Force caching the API response
  });
  const data = await res.json();

  return {
    props: { data },
  };
}

Explanation:

• The cache:'force-cache' setting tells Next.js application to store the API response instead of re-fetching it every time.
• This reduces load times and decreases server requests for frequently accessed data.

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Do: Optimize API Calls with Efficient Data Fetching

Why?
Making multiple API calls separately for related data can slow down your application and increase load time. Instead, combine requests when possible to reduce the number of network requests.

Example (Optimized Approach – Combining API Calls):

// Do: Fetch multiple pieces of data in a single API call
export async function getServerSideProps() {
  const response = await fetch('<https://api.example.com/data?include=users,posts,comments>');
  const data = await response.json();

  return {
    props: { data },
  };
}

Explanation:
Instead of making multiple API requests for users, posts, and comments separately, this optimized approach fetches all required data in a single API request, reducing latency and improving performance.

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Don’t: Make Separate API Calls for Each Data Type

Why?
Fetching data separately for different sections of the same page increases the number of API requests, leading to slower load times and increased server load.

Example (Bad Practice – Separate API Calls):

// Don't: Fetch each piece of data separately
export async function getServerSideProps() {
  const usersRes = await fetch('<https://api.example.com/users>');
  const postsRes = await fetch('<https://api.example.com/posts>');
  const commentsRes = await fetch('<https://api.example.com/comments>');

  const users = await usersRes.json();
  const posts = await postsRes.json();
  const comments = await commentsRes.json();

  return {
    props: { users, posts, comments },
  };
}

Explanation:
This approach makes three separate API calls, increasing response time and server load. Combining these calls into one request (as shown in the optimized example) significantly improves efficiency.

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7. Minimize Re-Renders in React

React applications rely on a component-based architecture, where each component can re-render when its state or props change. However, excessive re-renders can slow down your application, making it feel sluggish and unresponsive. Reducing unnecessary re-renders improves efficiency and ensures a smoother user experience.
Below are two key techniques to minimize re-renders in a React-based Next.js application:

1. Use React.memo to Prevent Unnecessary Re-Renders

What is React.memo?

React.memo is a higher-order component (HOC) that helps optimize functional components by memorizing their output. If the component’s props do not change, React will reuse the previously rendered output instead of re-rendering the component.

How does it work?

Normally, React re-renders a component whenever its parent re-renders, even if the props remain the same. This can lead to wasted renders and unnecessary computational load. React.memo prevents this by only re-rendering when the component’s props actually change.

Example: Using React.memo to Prevent Unnecessary Re-Renders

Not Optimized: Component Re-renders Even If Props Haven’t Changed

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const MyComponent = ({ data }) => {
  console.log("Rendering MyComponent...");
  return <div>{data}</div>;
};

• Problem: Every time the parent component re-renders, MyComponent also re-renders, even if data hasn’t changed.

Optimized: Using React.memo to Avoid Unnecessary Re-Renders

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const MyComponent = React.memo(({ data }) => {
  console.log("Rendering MyComponent...");
  return <div>{data}</div>;
});

• Solution: Now, MyComponent only re-renders when data changes.
• Benefit: This optimization significantly improves performance in large applications.

When Should You Use React.memo?

• Ideal for components that receive the same props frequently.
• Useful when re-renders impact performance, such as lists, tables, or frequently updated components.
• Not necessary for components that already change often due to state updates.

2. Optimize State Management to Avoid Unnecessary State Updates

Why is this important?

Managing state efficiently ensures that components only re-render when necessary. Every state update in a React component triggers a re-render, which can slow down performance if not handled properly.

A. Use Local State Wisely

Not Optimized: Updating State Unnecessarily

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const Counter = () => {
  const [count, setCount] = useState(0);

  const increment = () => {
    setCount(count + 1); // Direct state update on every click
  };

  return <button onClick={increment}>Count: {count}</button>;
};

• Problem: Each time the button is clicked, setCount(count + 1) triggers a full re-render, even if the same value is set.

Optimized: Only Update State When Necessary

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const Counter = () => {
  const [count, setCount] = useState(0);

  const increment = () => {
    setCount((prev) => prev + 1); // Using functional updates for efficiency
  };

  return <button onClick={increment}>Count: {count}</button>;
};

• Solution: Using setCount((prev) => prev + 1) ensures React batches state updates, avoiding unnecessary re-renders.

B. Use a State Management Library Efficiently (Redux, Zustand, or Context API)

For larger applications, global state management libraries like Redux or Zustand can help centralize and optimize state updates.
Not Optimized: Directly Updating State Everywhere

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const Profile = () => {
  const [user, setUser] = useState({ name: "John", age: 30 });

  const updateAge = () => {
    setUser({ name: user.name, age: user.age + 1 }); // Triggers full component re-render
  };

  return <button onClick={updateAge}>Increase Age</button>;
};

• Problem: Every update replaces the entire user object, triggering a full re-render.

Optimized: Use Zustand for Efficient State Management

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import create from "zustand";

const useUserStore = create((set) => ({
  user: { name: "John", age: 30 },
  incrementAge: () => set((state) => ({ user: { ...state.user, age: state.user.age + 1 } })),
}));

const Profile = () => {
  const { user, incrementAge } = useUserStore();

  return <button onClick={incrementAge}>Increase Age</button>;
};

• Solution: Zustand efficiently updates only the age field instead of replacing the whole object.
• Benefit: Minimizes re-renders, improving performance in state-heavy applications.

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Do: Use React.memo to Prevent Unnecessary Re-Renders

Why?
React.memo prevents re-rendering of components if their props haven’t changed, improving performance.

// Do: Use React.memo to avoid unnecessary re-renders
const MyComponent = React.memo(({ data }) => {
  console.log("Component rendered");
  return <div>{data}</div>;
});

// Usage
<MyComponent data="Optimized Data" />

Explanation:
In the above example, MyComponent will only re-render when the data prop changes. If the same prop is passed again, React will skip re-rendering, improving performance.

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Don’t: Pass Inline Functions or Objects as Props

Why?

Passing inline functions or objects as props creates a new reference on every render, causing unnecessary re-renders.

// Don't: Passing an inline function causes unnecessary re-renders
const MyComponent = ({ onClick }) => {
  return <button onClick={onClick}>Click Me</button>;
};

// Parent Component
const Parent = () => {
  return <MyComponent onClick={() => console.log("Button Clicked")} />;
};

Better Approach: Use useCallback to Memoize Functions

// Do: Use useCallback to memoize the function and prevent re-renders
const Parent = () => {
  const handleClick = useCallback(() => {
    console.log("Button Clicked");
  }, []);

  return <MyComponent onClick={handleClick} />;
};

Explanation:

• In the “Don’t” example, every time Parent re-renders, a new function reference is created, forcing MyComponent to re-render unnecessarily.
• In the “Do” example, useCallback ensures the function reference remains the same unless dependencies change, preventing unnecessary re-renders.

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8. Why Remove Unnecessary Imports?

In JavaScript and Next.js applications, imports play a crucial role in structuring the code and bringing in necessary modules, components, and dependencies. However, keeping unnecessary or unused imports can negatively impact performance, code quality, and maintainability. Removing unnecessary imports ensures that your application remains lightweight, optimized, and easier to manage.

Here’s why removing unnecessary imports is essential:

1. Reduced Bundle Size (Smaller JavaScript Files = Faster Load Times)

Why does bundle size matter?

• Every imported module adds extra weight to your JavaScript bundle.
• Large bundles take longer to download and process in the browser, leading to slower load times.

How unnecessary imports increase bundle size:
Not Optimized: Importing an entire library when only one function is needed

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import _ from "lodash"; // Imports the entire lodash library (heavy)
const clonedData = _.cloneDeep(data);

Optimized: Import only the required function

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import cloneDeep from "lodash/cloneDeep"; // Import only what's needed
const clonedData = cloneDeep(data);

Explanation:

• The first example imports the entire lodash library, which significantly increases the JavaScript bundle size.
• The optimized version imports only the cloneDeep function, reducing unnecessary code from being included in the bundle.

2. Improved Performance (Faster Parsing & Execution)

Why does performance improve?

• Smaller bundles load faster and execute more efficiently in the browser.
• Unused imports still get processed by bundlers like Webpack, increasing build time.

Example of an unnecessary import slowing execution:
Not Optimized: Importing unnecessary components

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import UnusedComponent from "./UnusedComponent"; // Not used anywhere
import React, { useState, useEffect } from "react";

Optimized: Remove unused imports

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import React, { useState } from "react"; // Removed useEffect since it's not needed

Explanation:

• The first example imports an unused component, which takes up space in the compiled bundle.
• The optimized version removes UnusedComponent and unnecessary hooks, improving execution speed.

3. Cleaner Code (Easier to Read & Maintain)

Why does it matter?

• Large projects often accumulate unnecessary imports over time.
• Removing them keeps the codebase organized, readable, and maintainable.

Not Optimized: Unnecessary and messy imports

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import { useState } from "react";
import { useEffect } from "react"; // Separate import for the same library
import axios from "axios"; // Not used anywhere in the file

Optimized: Clean and structured imports

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import { useState, useEffect } from "react"; // Consolidated import

Explanation:

• The first example has redundant imports (useState and useEffect should be grouped).
• The optimized version improves readability and structure.

4. Fewer Errors (Avoid Unexpected Issues & Conflicts)

Why can unused imports cause errors?

• Some unused imports may reference outdated or deprecated functions.
• Importing unused modules can sometimes lead to conflicts between dependencies.

Not Optimized: Keeping unnecessary imports that cause conflicts

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import axios from "axios";
import fetchData from "./utils"; // fetchData uses `fetch`, causing conflicts with axios

Optimized: Use only one API fetching method

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import fetchData from "./utils"; // Removed axios if not needed

Explanation:

• The first example imports both axios and fetchData, potentially leading to inconsistent API calls.
• The optimized version ensures that only one fetching method is used.

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9. Prefetching Links with next/link

Navigation speed is a crucial factor in user experience, and Next.js application provides a built-in feature to prefetch linked pages, making navigation feel instantaneous. Instead of waiting for a user to click a link and then fetching the page, Next.js application preloads the linked page in the background while it is in the viewport. This improves performance and reduces perceived load times. Next.js application can prefetch linked pages to improve navigation speed. Use the prefetch attribute in the next/link component to prefetch the page when the link is in the viewport.

How Does Prefetching Work in Next.js Application?

Next.js application automatically prefetches pages linked using next/link, provided that the link is visible in the viewport. This means that when a user hovers over or scrolls near a link, the page starts loading before the user even clicks on it.

By the time the user actually clicks the link, most of the page’s data has already been loaded, resulting in instant navigation.

How to Use prefetch in next/link

The next/link component in Next.js application comes with a prefetch attribute that controls whether a linked page should be prefetched in the background.

Example: Enabling Prefetching for Faster Navigation

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import Link from 'next/link';

const Navigation = () => {
  return (
    <nav>
      <ul>
        <li>
          <Link href="/about" prefetch={true}>
            About Us
          </Link>
        </li>
        <li>
          <Link href="/services">
            Services
          </Link> {/* Prefetching is enabled by default */}
        </li>
      </ul>
    </nav>
  );
};

export default Navigation;

Explanation:

• The first link (/about) explicitly enables prefetching with prefetch={true}.
• The second link (/services) automatically prefetches because prefetching is enabled by default in Next.js for all <Link> components.

When a user scrolls near these links, Next.js application starts preloading the respective pages in the background, making navigation faster.

When Should You Disable Prefetching?

While prefetching is beneficial in most cases, there are scenarios where disabling it can be useful, especially when dealing with large applications or limited bandwidth.

Disable prefetching if:

• The linked page is not frequently visited, and preloading it would be unnecessary.
• The page is heavy or dynamic, and you don’t want to load it until the user explicitly requests it.
• The application runs on slow networks or mobile devices, where background preloading might impact performance.

Example: Disabling Prefetching for Rarely Used Links

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import Link from 'next/link';

const Navigation = () => {
  return (
    <nav>
      <ul>
        <li>
          <Link href="/large-report" prefetch={false}>
            View Large Report
          </Link>
        </li>
      </ul>
    </nav>
  );
};

export default Navigation;

Explanation:

• In this example, the /large-report page will not be prefetched until the user actually clicks the link.
• This prevents unnecessary background loading of a large, rarely accessed page.

Benefits of Prefetching Links in Next.js Applications

1. Faster Navigation – Prefetched pages load instantly when clicked.
2. Better User Experience – Reduces waiting time and enhances seamless browsing.
3. Efficient Resource Utilization – Prefetching only loads necessary data, improving performance.
4. Optimized for SEO – Search engines favor fast-loading pages, improving ranking.

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Do: Enable Prefetching for Faster Navigation

Why?
Prefetching allows Next.js applications to load linked pages in the background before the user clicks, making navigation faster.

Example:

import Link from 'next/link';

const Navigation = () => {
  return (
    <nav>
      <ul>
        <li>
          <Link href="/about" prefetch={true}>
            About Us
          </Link>
        </li>
      </ul>
    </nav>
  );
};

export default Navigation;

Explanation:
Here, the prefetch={true} attribute tells Next.js to preload the /about page when it appears in the viewport. This improves user experience by making the navigation feel instant.

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Don’t : Disable Prefetching Unnecessarily

Why?
Disabling prefetching removes the performance advantage and can make navigation slower, especially on frequently visited pages.

Example:

import Link from 'next/link';

const Navigation = () => {
  return (
    <nav>
      <ul>
        <li>
          <Link href="/about" prefetch={false}>
            About Us
          </Link>
        </li>
      </ul>
    </nav>
  );
};

export default Navigation;

Explanation:
Setting prefetch={false} prevents Next.js application from preloading the linked page. This is only recommended if the page is rarely visited or if bandwidth needs to be conserved. Otherwise, it may lead to slower navigation.

After performing all these steps, check the speed and performance of your app using web performance tools like Google PageSpeed. A web performance tool can provide valuable information about application performance, such as:

• The time it takes to get the initial page.
• The time it takes to get the initial resources.
• The number of round trips transmitted.
• The amount of data transferred each trip.

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Conclusion:

According to my opinion, a slow Next.js application build process can be frustrating, but through systematic optimization, developers can drastically improve efficiency. By analyzing build performance, optimizing dependencies, leveraging caching, and refining configurations, applications can achieve faster build times and enhanced scalability. On the other hand, optimizing the performance of your Next.js application is an ongoing process that requires attention to detail and a combination of strategies. By leveraging features like SSG, ISR, SWR, dynamic imports, image optimization, and more, you can ensure your app is fast, efficient, and provides a superior user experience. Similarly, regularly monitoring performance and making data-driven decisions will help you maintain a high-performing Next.js application.

So, implement these strategies today to ensure a seamless and efficient Next.js development experience.

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