2nd/10_Wiki/Topics/AI_and_ML/Lazy-Loading-Strategies.md

id, title, category, status, canonical_id, aliases, duplicate_of, source_trust_level, confidence_score, verification_status, tags, raw_sources, last_reinforced, github_commit, tech_stack

id	title	category	status	canonical_id	aliases	duplicate_of	source_trust_level	confidence_score	verification_status	tags	raw_sources	last_reinforced	github_commit	tech_stack
wiki-2026-0508-lazy-loading-strategies	Lazy Loading Strategies	10_Wiki/Topics	verified	self	Lazy Load Deferred Loading On-Demand Loading	none	A	0.9	applied	frontend performance web react intersection-observer		2026-05-10	pending	language framework typescript react

Lazy Loading Strategies

매 한 줄

"매 필요한 순간에만 로드". 초기 bundle/네트워크 비용을 줄여 LCP, TTI 개선. Image, route, component, data 모두 적용 가능.

매 핵심

매 4가지 layer

1. Image lazy loading: loading="lazy", IntersectionObserver, blur placeholder.
2. Code splitting: dynamic import(), route-based, component-based.
3. Data lazy loading: virtual scroll, infinite scroll, pagination.
4. Resource hints: prefetch, preload, priority hints.

매 트리거

• viewport 진입 (IntersectionObserver).
• user interaction (click, hover).
• idle (requestIdleCallback).
• route navigation.

매 측정

• LCP: Largest Contentful Paint < 2.5s.
• CLS: lazy image 로 인한 layout shift 방지 (width/height 명시).
• JS bundle size: route 별 < 200KB gzip 권장.

💻 패턴

Native image lazy

<img src="hero.jpg" loading="lazy" decoding="async"
     width="1200" height="630" alt="..." />

IntersectionObserver (커스텀)

const io = new IntersectionObserver((entries) => {
  entries.forEach(e => {
    if (e.isIntersecting) {
      const img = e.target as HTMLImageElement;
      img.src = img.dataset.src!;
      io.unobserve(img);
    }
  });
}, { rootMargin: "200px" });

document.querySelectorAll("img[data-src]").forEach(img => io.observe(img));

React.lazy + Suspense (route)

import { lazy, Suspense } from "react";
const Settings = lazy(() => import("./pages/Settings"));

<Suspense fallback={<Spinner />}>
  <Routes>
    <Route path="/settings" element={<Settings />} />
  </Routes>
</Suspense>

Dynamic import on interaction

function ChartButton() {
  const [Chart, setChart] = useState<React.FC | null>(null);
  return (
    <>
      <button onClick={async () => {
        const m = await import("./HeavyChart");
        setChart(() => m.default);
      }}>Show chart</button>
      {Chart && <Chart />}
    </>
  );
}

Virtual scrolling (TanStack Virtual)

import { useVirtualizer } from "@tanstack/react-virtual";

const v = useVirtualizer({
  count: items.length,
  getScrollElement: () => parentRef.current,
  estimateSize: () => 48,
  overscan: 5,
});
return v.getVirtualItems().map(vi => (
  <div key={vi.key} style={{ transform: `translateY(${vi.start}px)` }}>
    {items[vi.index].name}
  </div>
));

React Query infinite scroll

const q = useInfiniteQuery({
  queryKey: ["posts"],
  queryFn: ({ pageParam = 0 }) => fetch(`/api?cursor=${pageParam}`).then(r => r.json()),
  getNextPageParam: (last) => last.nextCursor,
});

Idle-time prefetch

if ("requestIdleCallback" in window) {
  requestIdleCallback(() => import("./LikelyNextRoute"));
}

Next.js dynamic

import dynamic from "next/dynamic";
const Map = dynamic(() => import("./Map"), { ssr: false, loading: () => <p>...</p> });

매 결정 기준

자원	전략
Above-the-fold image	eager + preload
Below-the-fold image	loading="lazy"
큰 third-party (chart, map)	dynamic import on demand
Route component	route-based code split
1만+ list rows	virtual scroll
다음에 갈 가능성 큰 route	idle prefetch

기본값: native loading="lazy" for img, React.lazy for routes, virtual scroll > 200 rows.

🔗 Graph

• 부모: Web-Performance
• 변형: Code Splitting, Infinite-Scroll
• Adjacent: IntersectionObserver, Suspense

🤖 LLM 활용

언제: 페이지에 heavy component 가 conditional 로 필요, 큰 list, 이미지 많은 페이지. 언제 X: above-the-fold critical content, SEO-critical content (SSR 으로 처리).

❌ 안티패턴

• 모든 것을 lazy: critical hero image 까지 lazy → LCP 악화.
• width/height 누락: lazy image 로딩 후 layout shift (CLS↑).
• Suspense fallback 부재: blank flash.
• Interaction-block lazy: 클릭하면 1초 fetch → ux 나쁨, idle prefetch 병행.
• Spinner 남발: skeleton/blur placeholder 가 체감 좋음.

🧪 검증 / 중복

• web.dev "Lazy loading", MDN IntersectionObserver, React docs (lazy/Suspense).
• TanStack Virtual, Next.js dynamic 공식 문서.
• 신뢰도 A.

🕓 Changelog

날짜	변경
2026-05-08	Phase 1
2026-05-10	Manual cleanup — image/route/data 4 layer, IntersectionObserver/React.lazy/virtual 패턴