debian-mirror-gitlab/app/assets/javascripts/lazy_loader.js

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JavaScript
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import _ from 'underscore';
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export const placeholderImage =
'data:image/gif;base64,R0lGODlhAQABAAAAACH5BAEKAAEALAAAAAABAAEAAAICTAEAOw==';
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const SCROLL_THRESHOLD = 500;
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export default class LazyLoader {
constructor(options = {}) {
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this.intersectionObserver = null;
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this.lazyImages = [];
this.observerNode = options.observerNode || '#content-body';
const scrollContainer = options.scrollContainer || window;
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scrollContainer.addEventListener('load', () => this.register());
}
static supportsIntersectionObserver() {
return 'IntersectionObserver' in window;
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}
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searchLazyImages() {
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window.requestIdleCallback(
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() => {
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const lazyImages = [].slice.call(document.querySelectorAll('.lazy'));
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if (LazyLoader.supportsIntersectionObserver()) {
if (this.intersectionObserver) {
lazyImages.forEach(img => this.intersectionObserver.observe(img));
}
} else if (lazyImages.length) {
this.lazyImages = lazyImages;
this.checkElementsInView();
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}
},
{ timeout: 500 },
);
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}
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startContentObserver() {
const contentNode = document.querySelector(this.observerNode) || document.querySelector('body');
if (contentNode) {
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this.mutationObserver = new MutationObserver(() => this.searchLazyImages());
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this.mutationObserver.observe(contentNode, {
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childList: true,
subtree: true,
});
}
}
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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.supportsIntersectionObserver()) {
this.startIntersectionObserver();
} else {
this.startLegacyObserver();
}
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this.startContentObserver();
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this.searchLazyImages();
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}
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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 => {
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// We are using `intersectionRatio > 0` over `isIntersecting`, as some browsers did not ship the latter
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// See: https://gitlab.com/gitlab-org/gitlab-foss/issues/54407
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if (entry.intersectionRatio > 0) {
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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);
}
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scrollCheck() {
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window.requestAnimationFrame(() => this.checkElementsInView());
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}
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checkElementsInView() {
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const scrollTop = window.pageYOffset;
const visHeight = scrollTop + window.innerHeight + SCROLL_THRESHOLD;
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// Loading Images which are in the current viewport or close to them
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this.lazyImages = this.lazyImages.filter(selectedImage => {
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if (selectedImage.getAttribute('data-src')) {
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const imgBoundRect = selectedImage.getBoundingClientRect();
const imgTop = scrollTop + imgBoundRect.top;
const imgBound = imgTop + imgBoundRect.height;
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if (scrollTop <= imgBound && visHeight >= imgTop) {
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window.requestAnimationFrame(() => {
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LazyLoader.loadImage(selectedImage);
});
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return false;
}
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/*
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;
}
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return true;
}
return false;
});
}
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static loadImage(img) {
if (img.getAttribute('data-src')) {
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let imgUrl = img.getAttribute('data-src');
// Only adding width + height for avatars for now
if (imgUrl.indexOf('/avatar/') > -1 && imgUrl.indexOf('?') === -1) {
let targetWidth = null;
if (img.getAttribute('width')) {
targetWidth = img.getAttribute('width');
} else {
targetWidth = img.width;
}
if (targetWidth) imgUrl += `?width=${targetWidth}`;
}
img.setAttribute('src', imgUrl);
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img.removeAttribute('data-src');
img.classList.remove('lazy');
img.classList.add('js-lazy-loaded');
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img.classList.add('qa-js-lazy-loaded');
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}
}
}