WebPageTest Homepage WebPageTest, by Catchpoint Documentation

Lazy Loaded Images in Viewport

Return an array containing the sources of all images that have loading=lazy applied, but are visible within the initial viewport.

[lazy-in-viewport]
return new Promise(function (resolve) {
let lazyImages = document.querySelectorAll("img[loading=lazy]");
if (lazyImages.length == 0) {
return resolve([]);
}

let observer = new IntersectionObserver(function (entries, observer) {
observer.disconnect();
const eagerLoadingCandidates = entries
.filter(e => e.isIntersecting)
.map(e => e.target.src);
return resolve(JSON.stringify(eagerLoadingCandidates));
});
for (let img of lazyImages) {
observer.observe(img);
}
});