Lighthouse Tool - JavaScript Insights

Lighthouse Tool Practice

Lighthouse is an open-source automated tool for improving the quality of web pages. It can audit performance, accessibility, progressive web apps, SEO, and more.

How to Access Lighthouse

Open Chrome DevTools by pressing F12 or Ctrl+Shift+I (or Cmd+Option+I on Mac)
Click on the "Lighthouse" tab in the DevTools panel
Alternatively, you can access it through Chrome's menu: More Tools → Developer Tools → Lighthouse

Exercises

Click the buttons in each section below to add elements that will negatively impact Lighthouse scores
Run a Lighthouse audit by selecting either "Timespan" mode (for user interactions) or "Snapshot" mode (for current state)
Review your report and note which specific metrics were affected by the elements you added
Use the "Reset" buttons to fix the issues, then run another Lighthouse audit to compare the improved scores
Pay attention to which categories (Performance, Accessibility, Best Practices, SEO) are most affected by each change

Lighthouse Demo Elements

Performance Test Elements

Performance test area - click buttons above to load test elements

Accessibility Test Elements

Accessibility test area - click buttons above to load test elements

Best Practices Test Elements

Best practices test area - click buttons above to load test elements

SEO Test Elements

SEO test area - click buttons above to load test elements

Pro Tips for Lighthouse

Performance: Focus on Largest Contentful Paint (LCP), First Input Delay (FID), and Cumulative Layout Shift (CLS) - the Core Web Vitals
Throttling: Use the "Applied throttling" dropdown to simulate different network conditions
CI Integration: Consider running Lighthouse in your CI/CD pipeline using Lighthouse CI
Extensions: Disable browser extensions when running audits as they can affect performance measurements
Multiple runs: Run the audit multiple times and average the results for more accurate scoring
Incognito mode: For the most reliable results, run Lighthouse in incognito mode to avoid browser extensions interference

Expert Advice

Understanding Lighthouse Scores

Lighthouse scores are calculated based on a set of audits for each category:

0-49 (Red): Poor - significant improvements needed
50-89 (Orange): Needs improvement - addressing these issues will enhance user experience
90-100 (Green): Good - your page is performing well

Remember that scores can vary between runs due to network conditions and device performance. Focus on the specific recommendations rather than just the overall score.

Common Lighthouse Issues and Fixes

Eliminate render-blocking resources: Use async or defer for non-critical JavaScript and CSS
Properly size images: Serve images in proper dimensions and formats (WebP, AVIF)
Minimize main-thread work: Reduce JavaScript execution time and break up long tasks
Reduce unused JavaScript/CSS: Implement code splitting and tree shaking
Use accessible names for buttons/links: Ensure all interactive elements have descriptive labels

Lighthouse Hands-On 1