@exadel/esl/modules/esl-image/core/esl-image-iobserver.js

Exadel Smart Library (ESL) is the lightweight custom elements library that provide a set of super-flexible components

import { isMobile } from '../../esl-utils/environment/device-detector';
let iObserver;
/** ESL Image lazy loading IntersectionObserver instance */
export function getIObserver() {
    if (!iObserver) {
        iObserver = new IntersectionObserver(function (entries) {
            entries.forEach(handleViewport);
        }, {
            threshold: [0.01], // 0 + 1 are not correctly handled by all browsers
            rootMargin: isMobile ? '250px' : '500px' // rootMargin value for IntersectionObserver
        });
    }
    return iObserver;
}
function handleViewport(entry) {
    const image = entry.target;
    // Check that entry is going to appear in the viewport area
    if (entry.isIntersecting || entry.intersectionRatio > 0) {
        image.triggerLoad();
    }
}