JL Kruger
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Homepage (site/index.html): integration-v14 promoted, Writings section integrated with 33 pieces clustered by type (stories/essays/miscellany), Writings welcome lightbox, content frame at 98% opacity. Co-Authored-By: Claude Sonnet 4.6 <noreply@anthropic.com>
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1.8 KiB
title, impact, impactDescription, tags
| title | impact | impactDescription | tags |
|---|---|---|---|
| Use defer or async on Script Tags | HIGH | eliminates render-blocking | rendering, script, defer, async, performance |
Use defer or async on Script Tags
Impact: HIGH (eliminates render-blocking)
Script tags without defer or async block HTML parsing while the script downloads and executes. This delays First Contentful Paint and Time to Interactive.
defer: Downloads in parallel, executes after HTML parsing completes, maintains execution orderasync: Downloads in parallel, executes immediately when ready, no guaranteed order
Use defer for scripts that depend on DOM or other scripts. Use async for independent scripts like analytics.
Incorrect (blocks rendering):
export default function Document() {
return (
<html>
<head>
<script src="https://example.com/analytics.js" />
<script src="/scripts/utils.js" />
</head>
<body>{/* content */}</body>
</html>
)
}
Correct (non-blocking):
export default function Document() {
return (
<html>
<head>
{/* Independent script - use async */}
<script src="https://example.com/analytics.js" async />
{/* DOM-dependent script - use defer */}
<script src="/scripts/utils.js" defer />
</head>
<body>{/* content */}</body>
</html>
)
}
Note: In Next.js, prefer the next/script component with strategy prop instead of raw script tags:
import Script from 'next/script'
export default function Page() {
return (
<>
<Script src="https://example.com/analytics.js" strategy="afterInteractive" />
<Script src="/scripts/utils.js" strategy="beforeInteractive" />
</>
)
}
Reference: MDN - Script element