Key Takeaways

• Lazy loading is a technique that delays loading non-essential content until it's needed

• It significantly improves initial page load speed by up to 40-60%

• When implemented correctly, lazy loading can boost ad viewability and revenue

• Modern browsers support native lazy loading using the loading="lazy" attribute

• Proper implementation is crucial to avoid SEO issues with content crawling

What is Lazy Loading and Why Should You Care?

Picture this: a visitor lands on your content-heavy page with 15 images, 3 videos, and 5 ad units. Without lazy loading, their browser attempts to download EVERYTHING at once, creating a traffic jam of requests that slows down the page and might prompt them to bounce before seeing your content or ads.

Lazy loading fixes this by only loading what's immediately visible (above the fold), then gradually loading additional content as the user scrolls down.

It's like a smart waiter who brings your appetizer first, then only delivers the main course when you're ready for it - instead of crowding your table with every dish at once.

How Lazy Loading Actually Works

When a user visits your site, lazy loading follows this process:

1. Initial load: Only critical content appears (text, navigation, above-fold images and ads)

2. Placeholders: Reserved spaces hold position for content that will load later

3. Scroll detection: JavaScript monitors user scrolling behavior

4. Just-in-time loading: As content enters the viewport (visible area), resources are requested

For publishers, this means your site feels lightning-fast to users, even with lots of ads. The technical magic happens thru special JavaScript that monitors the user's scrolling and only triggers ad requests when they're about to enter the viewport.

The Performance Benefits Are Massive

In our tests across publisher sites, implementing lazy loading consistently delivers:

• 30-40% faster initial page load times

• 50-70% reduction in initial HTTP requests

• 25-35% decrease in bounce rates on content-heavy pages

Google's Web Dev team notes that lazy loading can reduce initial page weight by up to 90% on image-heavy pages. For publishers with high ad density, the impact is equally impressive.

One news site we worked with saw Time to Interactive improve from 12.8 seconds to just 3.2 seconds after implementing lazy loading for their ads and images!

Implementing Lazy Loading: Easier Than You Think

The good news? Implementing lazy loading has become much simpler with modern browsers.

Native Lazy Loading

Modern browsers now support native lazy loading using a simple HTML attribute:

<!-- For images -->
<img src="image.jpg" loading="lazy" alt="Description">

<!-- For iframes (like ad containers) -->
<iframe src="ad-code.html" loading="lazy"></iframe>

This built-in browser support means you dont need complex JavaScript for basic lazy loading. However, for more advanced control, especially with ads, custom implementation is still preferable.

Lazy Loading Ads

For ad units, implementation typically involves:

1. Delaying ad requests until they're near the viewport

2. Using intersection observer API to detect when ads are about to be visible

3. Setting appropriate thresholds (e.g., trigger loading when ad is 300px from viewport)

Here's a simplified example of the code pattern:

// Select all ad containers
const adContainers = document.querySelectorAll('.ad-container');

// Create an observer
const observer = new IntersectionObserver((entries) => {
  entries.forEach(entry => {
    // If ad container is near viewport
    if (entry.isIntersecting) {
      // Load the ad
      loadAdInContainer(entry.target);
      // Stop observing this container
      observer.unobserve(entry.target);
    }
  });
}, {
  // Load when ad is 300px from entering viewport
  rootMargin: '300px'
});

// Observe each ad container
adContainers.forEach(container => {
  observer.observe(container);
});

Common Mistakes to Avoid

Lazy loading seems simple, but there are potiential pitfalls:

1. Setting thresholds too tight: If you wait until an element is almost visible to load it, users might percieve lag. Start loading content when it's 200-300px away from the viewport.

2. Ignoring SEO implications: Search engines need to see your content! Ensure your lazy loading approach doesn't hide content from crawlers.

3. Forgetting about Core Web Vitals: Poor implementation can hurt metrics like Cumulative Layout Shift if elements resize upon loading.

4. Inconsistent ad behavior: Some publishers make the mistake of implementing different loading behaviors for content vs. ads, which can create jarring UX.

Impact on Ad Revenue and Viewability

When implemented correctly, lazy loading can actually increase ad revenue by:

1. Improving viewability scores - Ads load just before they're viewable, increasing the likelihood they'll be seen

2. Reducing accidental clicks - No more ads suddenly appearing under a user's finger/cursor

3. Supporting higher ad densities without performance penalties

4. Decreasing abandoned page loads due to slow-loading ad content

Newor Media reports that publishers implementing lazy loading see viewability increases of 15-30% on below-fold ad positions. Since viewability directly impacts CPMs on programmatic ads, this translates to higher revenue.

Is Lazy Loading Right for Your Site?

Lazy loading makes the most sense for:

• Content-heavy pages with multiple images/videos

• Sites with high ad density

• Long-form content where users scroll extensively

• Sites suffering from slow load times

• Mobile-heavy traffic (where bandwidth conservation matters)

For very simple sites with minimal media and few ads, the implementation complexity might outweigh the benefits.

Checking If Your Lazy Loading Works

After implementation, verify everything's working using:

1. Chrome DevTools Network Tab: Watch requests trigger as you scroll

2. Lighthouse Performance Audit: Compare before/after scores

3. Core Web Vitals metrics: Ensure LCP, FID, and CLS improve or stay steady

4. Google Ad Manager reporting: Monitor viewability metrics

If you see ad requests firing for units far below the fold before scrolling, your implementation needs adjustment.

The Takeaway

Lazy loading isn't just a performance trick – it's becoming a standard practice for professional publishers who care about user experience. By implementing it thoughtfully, you can deliver better performance, improved viewability, and ultimately higher ad revenue.

For most publishers, the question isn't whether to implement lazy loading, but rather how to optimize your specific implementation for maximum benefit.

Have questions about implementing lazy loading for your specific ad setup? Drop a comment below or reach out to our team.

This article is part of our Monetization Minis series, designed to help publishers understand key concepts quickly.