1.4 Rendering & JavaScript ✦MediumInferred
Render-blocking JS delaying paint
Scripts that block rendering push back when content paints, which hurts both users and the render budget Google allocates. I defer or async non-critical JavaScript.
What it is
Synchronous JS delays content rendering.
Why it matters
Slows render and can hurt page experience metrics.
How to fix it
Defer/async non-critical JS.
How to find it on your site
- Run Lighthouse or PageSpeed Insights and read the render-blocking resources list.
- Identify scripts loaded synchronously in the head.
- Add defer or async, or move them lower, where it is safe.
- Re-test paint timing after the change.
Cross-reference to ranking and citation factors
Faster paint helps Core Web Vitals and leaves more of the render budget for content. Render-blocking scripts work against both.
Impact
Low-medium; performance. Inferred.
Evidence
Avoid render-blocking resources for better page experience. Google Search Central, Understanding page experience in Google Search results; web.dev, Core Web Vitals (Google)
Sources