mediawiki-skins-Citizen/resources/scripts/lazyload.js

/*
 * Citizen - Lazyload JS
 * https://starcitizen.tools
 *
 * Lazyloading images with Native API or IntersectionObserver
 */

// Native API
if ("loading" in HTMLImageElement.prototype) {
    document.querySelectorAll("img.lazy").forEach(function(img) {
        img.setAttribute("src", img.getAttribute("data-src"));
        if (img.hasAttribute("data-srcset")) {
            img.setAttribute("srcset", img.getAttribute("data-srcset"));
        }
        img.classList.remove("lazy");
    });
} else {
    // IntersectionObserver API
    if (typeof IntersectionObserver !== "undefined" && "forEach" in NodeList.prototype) {
        var observer = new IntersectionObserver(function(changes) {
            if ("connection" in navigator && navigator.connection.saveData === true) {
                return;
            }
            changes.forEach(function(change) {
                if (change.isIntersecting) {
                    change.target.setAttribute("src", change.target.getAttribute("data-src"));
                    if (change.target.hasAttribute("data-srcset")) {
                        change.target.setAttribute("srcset", change.target.getAttribute("data-srcset"));
                    }
                    change.target.classList.remove("lazy");
                    observer.unobserve(change.target);
                }
            });
        });
        document.querySelectorAll("img.lazy").forEach(function(img) {
            observer.observe(img);
        });
    }
}