Split and defer non-critical JavaScript to improve page interactivity.
- Split and defer non-critical JavaScript to improve page interactivity1 cited source1 category
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Why this matters
Reducing initial JS payload and deferring non-essential scripts accelerates page responsiveness, improving Core Web Vital metrics like INP.
Hypothetical standard operating procedure
Adapt this example to your site, access, tools, and change process. It is our suggested procedure, informed by the sources below.
- Analyze JavaScript bundle sizes and identify critical vs non-critical scripts.
- Implement code splitting to separate route-specific JS bundles.
- Add defer or async attributes on script tags for non-critical JS.
- Test interaction responsiveness and INP metric via PageSpeed Insights or Web Vitals.
- Iterate to further reduce blocking JavaScript and optimize script loading order.
Watch for
Loading large JS bundles upfront blocks main thread, raising interaction latency and hurting SEO and UX.
Definition of done
Non-critical JS scripts use defer or async attributes and code splitting is applied per route.
Sources & attribution
Original checklist wording and example SOP by Best SEO Checklist, using source-grounded AI assistance. Editorial contact: Ted Kubaitis, @tedkubaitis on Teams. Check current source guidance before implementation.