76 lines
2.3 KiB
JavaScript
76 lines
2.3 KiB
JavaScript
import _ from 'underscore';
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export const placeholderImage = 'data:image/gif;base64,R0lGODlhAQABAAAAACH5BAEKAAEALAAAAAABAAEAAAICTAEAOw==';
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const SCROLL_THRESHOLD = 300;
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export default class LazyLoader {
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constructor(options = {}) {
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this.lazyImages = [];
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this.observerNode = options.observerNode || '#content-body';
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const throttledScrollCheck = _.throttle(() => this.scrollCheck(), 300);
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const debouncedElementsInView = _.debounce(() => this.checkElementsInView(), 300);
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window.addEventListener('scroll', throttledScrollCheck);
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window.addEventListener('resize', debouncedElementsInView);
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const scrollContainer = options.scrollContainer || window;
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scrollContainer.addEventListener('load', () => this.loadCheck());
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}
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searchLazyImages() {
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this.lazyImages = [].slice.call(document.querySelectorAll('.lazy'));
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if (this.lazyImages.length) {
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this.checkElementsInView();
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}
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}
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startContentObserver() {
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const contentNode = document.querySelector(this.observerNode) || document.querySelector('body');
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if (contentNode) {
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const observer = new MutationObserver(() => this.searchLazyImages());
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observer.observe(contentNode, {
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childList: true,
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subtree: true,
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});
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}
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}
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loadCheck() {
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this.searchLazyImages();
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this.startContentObserver();
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}
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scrollCheck() {
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requestAnimationFrame(() => this.checkElementsInView());
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}
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checkElementsInView() {
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const scrollTop = pageYOffset;
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const visHeight = scrollTop + 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();
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const imgTop = scrollTop + imgBoundRect.top;
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const imgBound = imgTop + imgBoundRect.height;
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if (scrollTop < imgBound && visHeight > imgTop) {
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LazyLoader.loadImage(selectedImage);
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return false;
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}
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return true;
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}
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return false;
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});
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}
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static loadImage(img) {
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if (img.getAttribute('data-src')) {
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img.setAttribute('src', img.getAttribute('data-src'));
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img.removeAttribute('data-src');
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img.classList.remove('lazy');
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img.classList.add('js-lazy-loaded');
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}
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}
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}
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