Future versions of Google Chrome will feature built-in support for lazy loading, a mechanism to defer the loading of images and iframes if they are not visible on the user's screen at load time.

This system will first ship with Chrome for Android and Google doesn't rule out adding it to desktop versions if tests go as planned.

The feature is called Blink LazyLoad, and as the name hints, it will implement the principle of "lazy loading" inside Chrome itself.

How lazy loading has helped improve page loading speed

By default, all browsers will load the entire web page when the user is accessing an URL. If the page is large, it takes more time to load, and as a side-effect of this longer page load time, the site may be downranked in Google search results.

For the past decade, website developers have implemented image lazy loading with the help of third-party JavaScript libraries loaded on their site.

These scripts work by loading only images seen at the top of the site, in the visible section of a page named "above the fold." Lazy loading scripts will delay loading images shown "below the fold" and only load them if the user scrolls down and the photos enter the user-visible area.

Now, according to a design document seen by Bleeping Computer, Google plans to add a lazy loading mechanism inside Chrome itself, which will work the same way.

The only difference is that it will defer both images and iframes, unlike most JS-based lazy loading scripts that only target "below the fold" images.

Tests show 18%-35% page load speed improvements

The obvious advantage is that pages will load faster and save bandwidth for users, especially on mobile connections.

Google engineers reported page load speed improvements varying from 18% to 35%, depending on the underlying network.

Other browser makers have been notified of the Chrome team's plan, but none have provided input if they plan to implement a similar feature.

Google also plans to add a mechanism to turn off built-in lazy loading if users choose to. This could be done via a new browser setting, or via a Chrome flag.

Some problems ahead

The downside is that Google will also have to re-do some existing Chrome features, like "Print" or "Save Page As," to load deferred images before executing their predefined actions (printing or saving a fully-rendered copy of the page).

Another potential issue may arise with users on intermittent connections, where images may fail to load when scrolling down the page, and the user may have no idea that there were supposed to be images on the page.

Google engineers will also have to take into account how their own system will interact with pre-existing JS-based lazy loading scripts, and avoid affecting site layouts after they roll out the feature.

Image credits: PACE, Bleeping Computer, Google