52 lines
1.4 KiB
JavaScript
52 lines
1.4 KiB
JavaScript
// @flow
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import type { ElementRef } from 'react';
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import { useEffect } from 'react';
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/**
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* Helper React hook for lazy loading images
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* @param elementRef - A React useRef instance to the element to lazy load.
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* @param {Number} [threshold=0.5] - The percent visible in order for loading to begin.
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* @param {Array<>} [deps=[]] - The dependencies this lazy-load is reliant on.
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*/
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export default function useLazyLoading(
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elementRef: { current: ?ElementRef<any> },
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threshold: number = 0.25,
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deps: Array<any> = []
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) {
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useEffect(() => {
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if (!elementRef.current) {
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return;
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}
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const lazyLoadingObserver = new IntersectionObserver(
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(entries, observer) => {
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entries.forEach((entry) => {
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if (entry.intersectionRatio >= threshold) {
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const { target } = entry;
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observer.unobserve(target);
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// useful for lazy loading img tags
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if (target.dataset.src) {
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// $FlowFixMe
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target.src = target.dataset.src;
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return;
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}
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// useful for lazy loading background images on divs
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if (target.dataset.backgroundImage) {
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target.style.backgroundImage = `url(${target.dataset.backgroundImage})`;
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}
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}
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});
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},
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{
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root: null,
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rootMargin: '0px',
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threshold,
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}
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);
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lazyLoadingObserver.observe(elementRef.current);
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}, deps);
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}
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