HouYunFei
fb79a15508
- 添加 sections 定义文件，包含性能优化各领域分类 - 添加规则模板文件，规范文档结构和标签定义 - 添加异步操作优化规则，包括防止瀑布流、并行化、延迟等待等 - 添加包大小优化规则，包括避免桶式导入、动态导入、预加载等 - 添加服务端性能优化规则，包括 API 路
1.8 KiB
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