🎯 Critical Rendering Path: Deep Dive into Browser Rendering Cycle
Category: general
Difficulty: hard
Understanding how browsers render web pages is essential for performance optimization. This guide explains the Critical Rendering Path (CRP), rendering stages, performance metrics, and practical optimization strategies. 💡 What is the Critical Rendering Path? The Critical Rendering Path is the sequence of steps a browser takes to: Parse HTML and CSS Construct the DOM and CSSOM Create the render tree Calculate layout Paint pixels on screen The CRP directly impacts First Contentful Paint (FCP) and Largest Contentful Paint (LCP), which are key Web Vitals metrics. Why it matters: Any resource that blocks the CRP delays when your page becomes visible and interactive. ⚠️ What is Render-Blocking? Render-blocking means the browser pauses or delays rendering while waiting for a resource to be fetched and processed. Critical Render-Blocking Resources: Blocks Rendering Impact ✅ Yes Highest priority JavaScript (default) Can modify DOM/CSSOM/styles ❌ No Ideal for most JavaScript (async) Runs independently ⚠️ Partial Use font-display: swap Images Loaded separately *May execute before rendering completes, but doesn't intentionally block it. Render-Blocking Impact on Performance: [code example]