Should you really ditch JavaScript libraries for native lazy loading solutions?

Why does Google warn against lazy loading libraries?

The main problem with JavaScript libraries for lazy loading lies in their mode of operation. Many rely on scroll events or complex detections that do not always trigger correctly during Googlebot's crawl. The bot does not scroll a page like a human; it simulates an initial viewport and then analyzes the rendered DOM.

As a result: an image configured for lazy loading via a JS library may remain invisible to the crawler if it is not within the initial viewport. Worse still, some libraries block the critical rendering path by injecting heavy JavaScript before essential resources are loaded. Google has said numerous times: anything that delays the First Contentful Paint or LCP is problematic.

What exactly is native lazy loading and Intersection Observer?

Native lazy loading (`loading="lazy"`) is an HTML5 attribute that all modern browsers have understood since 2019-2020. You add it to an `` or `` tag, and the browser automatically handles deferred loading without JavaScript. Zero dependencies, zero overhead, and most importantly: Googlebot understands it perfectly since its migration to the Chromium rendering engine.

The Intersection Observer API is a native JavaScript interface that detects when an element enters the viewport, without listening to scroll events (which are performance-intensive). This method is recommended if you need fine control over timing or trigger thresholds. Unlike old libraries, it does not impact the main thread and remains compatible with Googlebot's rendering pipeline.

Are all libraries really problematic?

No, and this is where Martin Splitt's statement lacks nuance. Some modern libraries like lazysizes (with the unveilhooks plugin) or vanilla-lazyload actually use Intersection Observer under the hood and only add a layer of fallback for older browsers. They only

Is this statement consistent with real-world observations?

Absolutely. Since 2020, there has been an increase in cases where sites lose indexing of their images because a poorly configured lazy loading library prevents Googlebot from seeing the actual `src`. The bot does not always trigger complex JavaScript listeners, and some libraries replace the `src` attribute with a data-attribute that Google ignores if the script does not execute correctly.

In contrast, sites that have migrated to loading="lazy" native or a clean implementation of Intersection Observer notice improved LCP (less blocking JavaScript) and better image indexing in Google Images. This is measurable in the Core Web Vitals and crawl logs. [To verify]: Google has never published quantitative data on the rendering failure rates by library type — we rely on use cases and reports from Search Console.

What are the limitations of this recommendation?

Native lazy loading does not allow customization of trigger thresholds. The browser decides when to load the image based on the distance to the viewport, and this behavior varies from browser to browser. If you need to load an image 500 pixels before it enters the viewport (to avoid a white flash), you’ll need to use Intersection Observer with a custom `rootMargin`.

Another point: some libraries offer advanced functionalities like CSS background-image lazy loading, dynamic responsive images, or LQIP (Low Quality Image Placeholder) placeholders. Native lazy loading only manages `` and ``. If your project requires these features, you won't be able to replace everything with the native attribute — but you can combine both approaches using Intersection Observer for specific cases.

When should you still use a library?

If you need to support older browsers (Internet Explorer, Safari pre-15.4), native lazy loading will not work, and you will need a polyfill or a lib with fallback. But let’s be clear: by 2025, native support will exceed 95% of global traffic. It’s up to you to decide if the maintenance cost of a lib is worth it for the remaining 5%.

Another legitimate case: React/Vue/Angular applications with complex components requiring fine control over the lifecycle. In this context, you can use Intersection Observer via a custom hook (like `react-intersection-observer`) instead of a monolithic lib. The key is to stick to solutions that do not interfere with Googlebot's rendering.

How to effectively migrate to native lazy loading?

Your first reflex: audit your images with a Screaming Frog or Oncrawl crawl in "JavaScript rendering" mode. Compare the source HTML and the rendered DOM to identify images whose `src` only appears after JS execution. These are your priority targets. If they use a data-attribute (like `data-src`), that's a red flag.

Then, replace custom attributes with a simple `loading="lazy"` on the `` tags. Keep standard `src` and `srcset` — no data-attributes. For above-the-fold images (visible without scrolling), do not add `loading="lazy"`, as it would delay the LCP. Reserve lazy loading for images below the fold.

What if I need advanced features?

For CSS background-images or non-`` elements, implement Intersection Observer directly. Create a lightweight script that observes elements with a `.lazy-bg` class, and apply the background via JavaScript only when the element enters the viewport. No need for a 50kb library for that — 20 lines of JS will suffice.

If you are using a modern framework (Next.js, Nuxt), take advantage of their optimized Image components that already manage intelligent lazy loading with Intersection Observer under the hood. Next.js Image, for example, combines lazy loading, modern formats (WebP/AVIF), and responsive sizing. It’s an all-in-one solution that adheres to Google's recommendations.

How to verify that my implementation works for Googlebot?

Use the URL Inspection tool in Google Search Console. Request live indexing and check the rendered screenshot. If your lazy-loaded images appear correctly, that’s a good sign. Also check the rendered HTML code ("More Info" tab > "HTML") to confirm that the `src` attributes are present.

Completing with a PageSpeed Insights or Lighthouse test. Look at the LCP and the audit "Defer offscreen images". If you see warnings about non-deferred images or blocking JavaScript, investigate. Finally, monitor your Core Web Vitals in real-world conditions via Search Console and the CrUX dashboard. A regression in LCP post-migration is a red flag.

• Audit images with a crawler in JS rendering mode to detect data-attributes
• Replace legacy libraries with native `loading="lazy"` on below-the-fold images
• Never apply `loading="lazy"` to above-the-fold images (LCP impact)
• Implement Intersection Observer manually for advanced cases (background-images, custom thresholds)
• Test Googlebot’s rendering via URL Inspection (Search Console) and verify the presence of `src`
• Monitor Core Web Vitals (especially LCP) before and after migration to detect any regression