How does lazy loading work?

When someone adds a resource to a web page, like an image, video, etc., the resource references a small placeholder. As a user browses the web page, the actual resource is cached by the browser and replaces the placeholder when the resource becomes visible on the user's screen.

How do I know if lazy loading is working?

You can check to see that a module is indeed being lazy-loaded with the Chrome developer tools. Open dev tools in Chrome by pressing Cmd+Option+i on Mac or Ctrl+Alt+i on PC and go to Network Tab.

Does lazy loading affect SEO?

Lazy loading images improves the user experience, first saving bandwidth for important content. Properly lazy loading your images does not prevent them from being indexed. And does not affect your website rankings .

How to Lazy Load Images With 4 Easy Ways

Why are lazy load images so good for your website, and what is the most efficient way to do so? Lazy load images not in the viewport can improve the performance and user experience. This is a detailed guide to the lazy loading of images.

Images are essential to all websites and applications today. Whether it's a marketing banner, a product image, or a logo, you can't imagine a website without images. Unfortunately, the image's large size is the number one cause of slow page loading times.

What is Lazy Load Images Means?

A picture is worth a thousand words, so it’s no wonder many websites rely on graphics to convey their messages. It’s not bad since we’re primarily visual types of users.

Still, the number of images used on a website directly impacts the page load speed. To face this challenge, web designers use the lazy load images technique.

Why Do You Need to Use Lazy Load Images?

Lazy loading is a web-design technique that intentionally postpones loading offscreen images until a user scrolls down the page; meanwhile, placeholders are used.

average website speed load time with different web page sizes — Average Website Speed Load Time with Different Page Sizes

There are several reasons why you might want to use lazy-load images on your website:

Improved performance: Lazy loading images can significantly improve the performance of your website by deferring the loading of images until they are actually needed. This can reduce the initial page load time, making your website feel more responsive and improving the user experience.
Reduced bandwidth usage: Lazy loading images can also help reduce bandwidth usage by only loading images visible to the user. This can significantly benefit users with slow internet connections or limited data plans.
Better SEO: Lazy loading images does not affect SEO in any negative way. In fact, some studies have shown that lazy loading can improve SEO by improving the user experience and reducing bounce rates.

Here are some of the benefits of using lazy load images:

Faster page load times: Lazy loading images can significantly improve the loading speed of your website by only loading images that are visible to the user. This can make your website feel more responsive and improve the user experience.
Reduced bandwidth usage: Lazy loading images can also help reduce bandwidth usage by only loading images visible to the user. This can significantly benefit users with slow internet connections or limited data plans.
Better user experience: Lazy loading images can provide a better user experience by ensuring that only the images that are relevant to the user are loaded. This can help to reduce distractions and improve the overall browsing experience.

Here are some of the drawbacks of using lazy load images:

Initial load time: The initial load time of your website may be slightly slower when using lazy-loading images, as the images will not be loaded until they are visible to the user. However, this delay is usually very short and is often imperceptible to the user.
Placeholder images: Lazy loading images often display placeholder images until the actual image is loaded. These placeholder images can be distracting or ugly, so it is crucial to choose them carefully.
Technical complexity: Lazy loading images can be technically complex to implement, especially if you are unfamiliar with JavaScript. However, many libraries and tools can help to make the process easier.

Overall, the benefits of using lazy load images outweigh the drawbacks. If you want to improve your website's performance and user experience, lazy loading images is a great option.

Now you can lazy load images quickly using these simple ways. If you want to fix your site's core web vitals statistics and increase site speed, it becomes vital that you lazy load images. So your site does not load all together in one go, and only those images which need to be loaded above the page fold load first and do not slow down the rest of the page loading speed.

1. Add JS Libraries Scripts

How to Lazy Load Images With 4 Easy Ways — Lazy Load Scripts – How to Lazy Load Images

Сompared to writing code from scratch, grabbing a JS library requires the minimum effort to lazy load images efficiently. If you don’t really care what’s inside as long as it does the job for you, here’s a list of JS libraries recommended by Google to lazy load images:

Add any of the above scripts in the footer of your web pages to lazy load images. First, you need to download it. It will load the script on all your pages.

Here is what typically the code lazy sizes will look like:

<script src="lazysizes.min.js" async=""></script>

You can either upload it on your server or use a CDN. You can also source the latest code from cdnjs and use the power of CDN to deliver the script faster across the world or use your own CDN to lazy load images.

<script src="https://cdnjs.cloudflare.com/ajax/libs/lazysizes/5.2.2/lazysizes.min.js"></script>

Why Lazysizes When There Are Many Scripts?

It is an SEO-friendly lazy loader for images as it does not block images from Googlebot even if they are not scrolled and loaded. And, of course, there are other high-performance features you can read up on their site.

Even Google recommends it in several support pages for Lighthouse and other core vital speed tests to lazy load images.

2. Edit Image Src Codes

The script will only work on those images where the image src has been replaced by image data-src, and this will help the script convert these images to image src when these images are loaded upon page scroll.

<img src="image.jpg" />

You need to change it by adding data- as follows to lazy load images.

<img data-src="image.jpg" />

If you are like us and use srcset to make images sharper on 4K screens, you must replace it with a data-srcset.

<img src="image.jpg" srcset="image2x.jpg 2x" />

will be edited to

<img data-src="image.jpg" data-srcset="image2x.jpg 2x" />

3. Add LazyLoad Class

In this next step, you need to add a specific class to all the images, which will help the script identify that these images need to be lazy-loaded, and then it will work like magic.

The class to be added is lazyload, and you need to add it to whichever images you want to lazy load. Else, the script will not defer the loading of your images to lazy load images.

<img data-src="image.jpg" class="lazyload" />

and the code with srcset will look like this

<img data-src="image.jpg" data-srcset="image2x.jpg 2x" class="lazyload" />

So that’s it.

Now you can quickly scroll your long web page with images and see how images load delayed with page scroll to that area. You can also use site speed tests and see that those images are no longer counted in your page load times as they are not loaded.

What if You Cannot Edit all Image Tags?

If you are using WordPress, it would be better to use a WordPress plugin to automatically change image src codes in bulk. Most site optimization plugins now have the lazyload images script available, and you can load it with a click.

4. Use a Plugin if You Are Using WordPress

There are a couple of options out there that can give you lazy loading. The most popular solutions for lazy load images are:

Lazy Load by WP Rocket
a3 Lazy Load
Optimole

All these plugins will handle the lazy load images for you automatically. Each also comes with some excellent side features to lazy load images.

Lazy Load by WP Rocket

You can lazy load thumbnails, all images in post content, widget text, avatars, smilies, and iframes. No JavaScript library, such as jQuery, is used, and the script weight is less than 10KB.

Lazy Load by WP Rocket also lazy loads of YouTube videos and replaces them with a thumbnail.
How To Lazy Load Images

Here is an example of putting in functions.php files that disable lazyload on posts:

add_action( 'wp', 'deactivate_rocket_lazyload_on_single' );
function deactivate_rocket_lazyload_on_single() {
    if ( is_single() ) {
        add_filter( 'do_rocket_lazyload', '__return_false' );
    }
}

You can also replace YouTube iframes with a preview thumbnail to speed up your website's loading time.

DOWNLOAD LAZY LOAD BY WP-ROCKET

a3 Lazy Load

A3 Lazy Load is a Mobile-Oriented, very simple-to-use plugin that will speed up the site's page load speed. The more content-heavy your site, the better the plugin will perform, and the more you will see performance improvements.

Images are the number one element that slows page load and increases bandwidth use. Turn load images from the a3 Lazy Load admin panel by a3 Lazy Load ON | OFF. For more flexibility when ON, you can choose to ON | OFF lazy load for images in:

Post, Pages, and Custom Post Types (All Content Areas).
Widgets (Sidebar, header, and footer).
Apply to post thumbnails.
Apply to Gravatars.
Fully compatible with WordPress embed posts on any site.
It makes embedding the post load much faster.

DOWNLOAD a3 LAZY LOAD

Optimole

Optimole is the all-in-one solution to all of your image optimization needs. Optimole makes it easy to clean up your heavy images and bloaty pages with lazy load images with full automation and a range of revolutionary features.

What makes Optimole so unique?

Smaller images. Same quality.
Fully automated; set and forget.
Supports all image types.
Supports both Retina and WebP images.
Serves images from a global CDN for free.
Optimizes based on the visitor’s device (no more guesswork and width estimations).
Full support for page builders like Elementor.
Lazy load without jQuery (better).
A fully functional free version.

So, if you have been looking for one plugin that provides lazy loading with a CDN and perfectly sized images, then Optimole is perfect for you.

DOWNLOAD OPTIMOLE

Are There Any Benefits of Native Lazy Loading?

The advent of native lazy loading in modern web browsers provides significant performance, efficiency, and user experience improvements for loading images on the web. Lazy loading refers to deferring the loading of non-critical offscreen images until the user scrolls near them. Doing this natively within the browser provides vital advantages compared to relying on external libraries and polyfills.

Firstly, native lazy loading improves page load speeds and perceived performance by reducing initial bandwidth usage and the number of requests made to the server. Only loading images as they become visible makes the initial page payload lighter, allowing above-the-fold content to render more quickly. Users perceive faster load times when placeholders are displayed instead of blank spaces.

Secondly, lazy loading reduces data usage for the end user. Studies show over 60% of images are never seen by users on long web pages. By avoiding downloading unseen images, users save on data costs and experience faster scrolling due to lighter page weight. Sites also benefit from reduced hosting bandwidth usage.

Additionally, native implementation avoids the need for complex JavaScript libraries and intersections observers for lazy loading. Native support is faster and more efficient, making lazy loading trivial to implement in HTML alone. Browser optimization also ensures maximum performance.

Native lazy loading improves user experience by enabling smooth scrolling and reducing data costs. Faster load times, quicker scrolling response, and seamless image rendering provide a polished experience to website users.

Native lazy loading boosts efficiency, speed, and user experience through delayed loading offscreen images. With native browser support, sites can reap these benefits using a clean, performant implementation of a once-complex technique. The web community embraces native lazy loading as a new best practice for performant image loading.

FAQs About How to Lazy Load Images:

How does lazy loading work?

When someone adds a resource to a web page, like an image, video, etc., the resource references a small placeholder. As a user browses the web page, the actual resource is cached by the browser and replaces the placeholder when the resource becomes visible on the user's screen.
How do I know if lazy loading is working?

You can check to see that a module is indeed being lazy-loaded with the Chrome developer tools. Open dev tools in Chrome by pressing Cmd+Option+i on Mac or Ctrl+Alt+i on PC and go to Network Tab.
Does lazy loading affect SEO?

Lazy loading images improves the user experience, first saving bandwidth for important content. Properly lazy loading your images does not prevent them from being indexed. And does not affect your website rankings.