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import { debounce, throttle } from 'lodash';
export const placeholderImage =
'data:image/gif;base64,R0lGODlhAQABAAAAACH5BAEKAAEALAAAAAABAAEAAAICTAEAOw==';
const SCROLL_THRESHOLD = 500;
export default class LazyLoader {
constructor(options = {}) {
this.intersectionObserver = null;
this.lazyImages = [];
this.observerNode = options.observerNode || '#content-body';
const scrollContainer = options.scrollContainer || window;
scrollContainer.addEventListener('load', () => this.register());
}
static supportsNativeLazyLoading() {
return 'loading' in HTMLImageElement.prototype;
}
static supportsIntersectionObserver() {
return Boolean(window.IntersectionObserver);
}
searchLazyImages() {
window.requestIdleCallback(
() => {
const lazyImages = [].slice.call(document.querySelectorAll('.lazy'));
if (LazyLoader.supportsNativeLazyLoading()) {
lazyImages.forEach((img) => LazyLoader.loadImage(img));
} else if (LazyLoader.supportsIntersectionObserver()) {
if (this.intersectionObserver) {
lazyImages.forEach((img) => this.intersectionObserver.observe(img));
}
} else if (lazyImages.length) {
this.lazyImages = lazyImages;
this.checkElementsInView();
}
},
{ timeout: 500 },
);
}
startContentObserver() {
const contentNode = document.querySelector(this.observerNode) || document.querySelector('body');
if (contentNode && !this.mutationObserver) {
this.mutationObserver = new MutationObserver(() => this.searchLazyImages());
this.mutationObserver.observe(contentNode, {
childList: true,
subtree: true,
});
}
}
stopContentObserver() {
if (this.mutationObserver) {
this.mutationObserver.takeRecords();
this.mutationObserver.disconnect();
this.mutationObserver = null;
}
}
unregister() {
this.stopContentObserver();
if (this.intersectionObserver) {
this.intersectionObserver.takeRecords();
this.intersectionObserver.disconnect();
this.intersectionObserver = null;
}
if (this.throttledScrollCheck) {
window.removeEventListener('scroll', this.throttledScrollCheck);
}
if (this.debouncedElementsInView) {
window.removeEventListener('resize', this.debouncedElementsInView);
}
}
register() {
if (!LazyLoader.supportsNativeLazyLoading()) {
if (LazyLoader.supportsIntersectionObserver()) {
this.startIntersectionObserver();
} else {
this.startLegacyObserver();
}
}
this.startContentObserver();
this.searchLazyImages();
}
startIntersectionObserver = () => {
this.throttledElementsInView = throttle(() => this.checkElementsInView(), 300);
this.intersectionObserver = new IntersectionObserver(this.onIntersection, {
rootMargin: `${SCROLL_THRESHOLD}px 0px`,
thresholds: 0.1,
});
};
onIntersection = (entries) => {
entries.forEach((entry) => {
// We are using `intersectionRatio > 0` over `isIntersecting`, as some browsers did not ship the latter
// See: https://gitlab.com/gitlab-org/gitlab-foss/issues/54407
if (entry.intersectionRatio > 0) {
this.intersectionObserver.unobserve(entry.target);
this.lazyImages.push(entry.target);
}
});
this.throttledElementsInView();
};
startLegacyObserver() {
this.throttledScrollCheck = throttle(() => this.scrollCheck(), 300);
this.debouncedElementsInView = debounce(() => this.checkElementsInView(), 300);
window.addEventListener('scroll', this.throttledScrollCheck);
window.addEventListener('resize', this.debouncedElementsInView);
}
scrollCheck() {
window.requestAnimationFrame(() => this.checkElementsInView());
}
checkElementsInView() {
const scrollTop = window.pageYOffset;
const visHeight = scrollTop + window.innerHeight + SCROLL_THRESHOLD;
// Loading Images which are in the current viewport or close to them
this.lazyImages = this.lazyImages.filter((selectedImage) => {
if (selectedImage.getAttribute('data-src')) {
const imgBoundRect = selectedImage.getBoundingClientRect();
const imgTop = scrollTop + imgBoundRect.top;
const imgBound = imgTop + imgBoundRect.height;
if (scrollTop <= imgBound && visHeight >= imgTop) {
window.requestAnimationFrame(() => {
LazyLoader.loadImage(selectedImage);
});
return false;
}
/*
If we are scrolling fast, the img we watched intersecting could have left the view port.
So we are going watch for new intersections.
*/
if (LazyLoader.supportsIntersectionObserver()) {
if (this.intersectionObserver) {
this.intersectionObserver.observe(selectedImage);
}
return false;
}
return true;
}
return false;
});
}
static loadImage(img) {
if (img.getAttribute('data-src')) {
img.setAttribute('loading', 'lazy');
let imgUrl = img.getAttribute('data-src');
// Only adding width + height for avatars for now
if (imgUrl.indexOf('/avatar/') > -1 && imgUrl.indexOf('?') === -1) {
const targetWidth = img.getAttribute('width') || img.width;
imgUrl += `?width=${targetWidth}`;
}
img.setAttribute('src', imgUrl);
img.removeAttribute('data-src');
img.classList.remove('lazy');
img.classList.add('js-lazy-loaded');
img.classList.add('qa-js-lazy-loaded');
}
}
}
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