Understanding Network Performance Analysis
Interactive Network Demo
Loading Strategies Explained
- loading="lazy": Defer loading until near viewport
- loading="eager": Load immediately
- rel="preload": High-priority fetch
- rel="prefetch": Low-priority fetch for future use
- defer: Execute script after HTML parsing
- async: Load and execute script asynchronously
- type="module": Load as ES module
- preload="none"/"metadata"/"auto": Media loading hints
What Are Render-Blocking Resources?
Render-blocking resources are scripts (JavaScript) and stylesheets (CSS) that prevent a web page from rendering until they are downloaded and processed, thus delaying the initial display of content.
Understanding Network Performance in DevTools
Visual Indicators
- 🔴 Red triangle - Render blocking request
- 🎨 Color codes next to Network track show request types
- ➡️ Click request to see dependency arrows
Request Details (Hover to See)
- 📍 Full URL
- ⏱️ Total load time
- ⚡ Priority level
- 🔄 Loading stages
Timeline Components
- |— Left line: Initial connection
- □ Light section: Server wait time
- ■ Dark section: Download time
- —| Right line: Processing time
Pro Tips
- Right-click → "Reveal in Network panel" for details
- Check Summary tab for priority information
- Monitor render-blocking resources
Performance Optimization Tips
- Use async/defer for non-critical scripts
- Implement lazy loading for images
- Prioritize critical resources
- Minimize render-blocking resources