Modern websites often have lots of images, videos, and scripts. Loading everything at once can make pages slow and frustrating. Luckily, there are easy ways to control what loads when: preload speeds up important stuff, prefetch gets ready for users’ next steps, and lazy loading waits until something is really needed. Knowing how and when to use each keeps your site fast and your visitors happy.
What Is Preload?
Preload is a way to prioritise critical resources by telling the browser to fetch them as soon as possible, ahead of when it normally would discover them in the HTML or CSS. This is essential for resources like fonts, hero images, or critical CSS/JS.
Example:
Use preload only for critical assets needed immediately for the first screen to show faster. Excessive preloading can hurt performance.
What Is Prefetch?
Prefetch prepares resources for future navigation, but keeps their priority low so they don’t slow the current page load. It lets browsers download assets the user might need next while respecting network bandwidth.
Example:
Prefetch is perfect for loading next-page scripts, styles, or images in the background to speed up navigation later.
What Is Lazy Loading?
Lazy loading means delaying the loading of non-critical resources until they are actually needed—like images or videos below the fold, scripts needed only after user interaction, or additional page content.
Modern browsers support native lazy loading:
Lazy loading reduces initial page weight and speeds up first load. Check out our blog post Lazy Loading in React.js to know more about how lazy loading works in React.js.
How <link rel="preload"> Can Improve Your Page Speed
Preloading critical fonts or images can drastically reduce Largest Contentful Paint (LCP), improving user perception and SEO ranking. Avoid preloading too many assets, which can overwhelm slow connections.
Using Prefetch to Speed Up Future Navigation
By prefetching resources like JavaScript chunks or entire HTML pages before the user requests them, you can make page transitions almost instant on repeat visits. Combine with lazy loading for the best user experience.
Advanced frameworks like Next.js and Gatsby automatically prefetch when links become visible in the viewport.
Lazy Loading Images & Videos: Best Practices for Web Performance
- Use native loading="lazy" where supported.
- For wide browser support, use Intersection Observer polyfills.
- Prioritise loading of above-the-fold assets.
- Resize images for responsive lazy loading.
- Monitor LCP to ensure important assets load quickly.
SEO Considerations when Lazy Loading Content
- Ensure lazy content is within HTML or accessible via JavaScript for search engines.
- Provide fallback content with <noscript> tags for old browsers and bots.
- Test lazy-loaded content with Google’s Mobile-Friendly and Rich Results test tools.
Lazy Loading Fallbacks & SEO: Making Sure Search Engines See Your Content
Common Mistakes with Preload / Prefetch and How to Avoid Them
- Preloading too many resources
- Forgetting to add an attribute with preload, causing double downloads
- Using prefetch indiscriminately, wasting bandwidth
- Lazy loading critical above-the-fold content
- No fallback for lazy-loaded content is hurting SEO