Lazy Loading
Sitecheck Team
A technique that defers loading of non-critical resources (images, scripts, iframes) until they are needed, typically when they scroll into view.
Lazy loading delays the download of off-screen resources until the user scrolls near them. The native HTML approach uses the loading="lazy" attribute on <img> and <iframe> elements and is supported in all modern browsers.
Why it matters: Images are typically the largest assets on a page. Loading all of them upfront wastes bandwidth for content the user may never see, directly hurting LCP and TTFB for users on slow connections.
Quick tips:
- Never lazy-load the hero/above-the-fold image — it will delay LCP.
- Add explicit
widthandheightattributes to images to prevent CLS. - For JavaScript-heavy SPAs, also consider route-level code splitting as a complementary technique.
See also: Core Web Vitals, LCP, CLS.