Examples of Performance Debugging with Lighthouse

Explore three practical examples of using Lighthouse for performance debugging to enhance your web applications.
By Jamie

Introduction to Performance Debugging with Lighthouse

Lighthouse is a powerful open-source tool from Google that helps developers optimize web applications. It provides insights into performance, accessibility, SEO, and best practices. This article offers three diverse examples of performance debugging using Lighthouse, illustrating how you can identify and resolve issues to enhance your website’s performance.

Example 1: Identifying Render-Blocking Resources

Context

In web development, render-blocking resources can significantly slow down the loading time of a page. This is particularly crucial for e-commerce websites, where speed can impact conversion rates.

When you run a Lighthouse audit on your site, it can report render-blocking JavaScript and CSS files that prevent the page from displaying quickly. By addressing these issues, you can enhance the user experience and improve SEO rankings.

Example

  1. Open Chrome DevTools (F12 or right-click and select ‘Inspect’).
  2. Navigate to the ‘Lighthouse’ tab.
  3. Select the categories you want to audit, such as Performance.
  4. Click on ‘Generate report’.
  5. In the report, check the ’Opportunities’ section for ‘Eliminate render-blocking resources’.
  6. Click on the suggested items to see specific files and recommendations on how to load them asynchronously or defer their loading.

Notes

  • Consider using async or defer attributes in your script tags to optimize how your JS files are loaded.
  • Ensure that critical CSS is loaded inline to improve the First Contentful Paint (FCP).

Example 2: Improving Largest Contentful Paint (LCP)

Context

Largest Contentful Paint (LCP) measures the time it takes for the largest visible content element to load. It is a critical metric in Google’s Core Web Vitals. Slow LCP can lead to user frustration and a higher bounce rate.

Using Lighthouse, web developers can diagnose issues affecting LCP and implement changes that lead to faster loading of crucial content like images or headers.

Example

  1. Run a Lighthouse audit in Chrome DevTools.
  2. Look for the ‘Performance’ score in the report.
  3. Identify the ‘Metrics’ section, focusing on LCP.
  4. Lighthouse may indicate large images or slow server responses as issues.
  5. Optimize images using formats like WebP, and ensure they are appropriately sized for display.
  6. Consider using a Content Delivery Network (CDN) to serve images faster.

Notes

  • Aim for an LCP of 2.5 seconds or less for optimal user experience.
  • Regularly monitor your LCP metric as part of your website maintenance routine.

Example 3: Addressing Excessive JavaScript Execution Time

Context

Excessive JavaScript execution time can lead to sluggish performance, affecting user interaction and engagement. For dynamic web applications, reducing this execution time is vital for maintaining a responsive user interface.

Lighthouse provides insights into scripts that are taking too long to execute, helping developers pinpoint and optimize these bottlenecks.

Example

  1. Launch Chrome DevTools and run a Lighthouse audit.
  2. Access the ‘Performance’ report.
  3. Look for the ‘JavaScript Execution Time’ metric in the ‘Metrics’ section.
  4. Identify scripts that take up a significant percentage of the execution time.
  5. Optimize these scripts by minimizing their size or using code-splitting techniques to load only necessary scripts.
  6. Use web workers for heavy computations to offload processing from the main thread.

Notes

  • Keep JavaScript bundles as small as possible to enhance loading times.
  • Regularly profile your JavaScript performance to identify new bottlenecks as your application evolves.