バンドル分析とパフォーマンス監査

Welcome to Bundle Analysis and Performance Audits! In modern web development, speed is key. Users expect fast loading times, and search engines reward performant sites.

This lesson will equip you with tools and techniques to understand what makes your Next.js application tick, identify bottlenecks, and ultimately make it faster.

When you build a Next.js application for production, all your code (JavaScript, CSS, assets) is processed and combined into one or more files called bundles.

• Faster Loading: Smaller bundles download quicker.
• Better UX: A fast site means happier users.
• SEO Boost: Search engines favor performant websites.
• Cost Savings: Less data transferred can mean lower hosting costs.

The @next/bundle-analyzer is an essential tool that helps you visualize the contents of your Next.js production bundles. It creates an interactive treemap that shows exactly which modules and dependencies contribute to your app's total size.

This visual report makes it easy to spot large libraries or duplicated code that might be slowing down your application.

First, you need to install the package as a development dependency in your Next.js project. Open your terminal in your project's root directory and run:

Next, you'll update your next.config.js file to enable the analyzer. This tells Next.js to generate the bundle reports when you build your application.

Now that it's configured, you can generate the bundle report. You'll typically do this by setting an environment variable before running your build command:

After the build completes, the reports (e.g., .next/analyze/client.html) will be generated. You can then open them in your browser to explore!

The bundle analyzer report is an interactive treemap. Here's what to look for:

• Large Rectangles: Indicate large modules or libraries.
• Red/Yellow Areas: Often highlight areas that contribute significantly to bundle size.
• Duplicates: Sometimes, different versions of the same library can be bundled.
• Unused Code: Can help you identify dependencies you might not need.

Hover over sections to see file sizes and paths.

Once you've identified large parts of your bundle, here are common ways to optimize:

• Dynamic Imports (Code Splitting): Load components or libraries only when needed.
• Tree Shaking: Ensure unused code from imported modules is removed.
• Gzip/Brotli Compression: Server-side compression reduces file transfer size.
• Remove Unused Libraries: Audit your dependencies and remove those not in use.
• Optimize Images: Use next/image and appropriate formats.

Beyond bundle size, Google Lighthouse is a powerful tool built into Chrome DevTools that performs a comprehensive audit of your web page. It checks for:

• Performance: Metrics like First Contentful Paint, Largest Contentful Paint.
• Accessibility: How usable your app is for everyone.
• Best Practices: General web standards.
• SEO: Search engine optimization factors.

Run it on your production build to get actionable insights!

Which of the following are effective strategies for reducing your Next.js application's bundle size or improving its performance?

Great job! You've learned how to analyze and optimize your Next.js application's performance:

• We explored what a bundle is and why its size matters.
• You learned to set up and interpret reports from @next/bundle-analyzer.
• We covered key optimization techniques like dynamic imports and tree shaking.
• Finally, we introduced Google Lighthouse for comprehensive performance audits.

Keep these tools in your arsenal to build faster, more efficient Next.js applications!