f7cf21b661
## Issue #6332 <Thumbnail lazy-loader is too slow || Use browser-level lazy-loading> ## Change Switch from "threshold-based check" to "viewport distance comparison" using the `rootMargin` parameter. The root is the viewport. This change makes it closer to the native `loading="lazy"` behavior, where it starts to load when approaching the viewport. Chrome I believe uses 3000px distance -- I think 500px is a good compromise for now. Can adjust further. ## Future - We are currently creating N instances of IntersectionObserver. - https://developers.google.com/web/updates/2016/04/intersectionobserver - "If you need to observe multiple elements, it is both possible and advised to observe multiple elements using the same IntersectionObserver instance by calling observe() multiple times." This would probably need a refactor to make ClaimList (or something higher) own the IntersectionObserver.
67 lines
1.9 KiB
JavaScript
67 lines
1.9 KiB
JavaScript
// @flow
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import type { ElementRef } from 'react';
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import React, { 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 yOffsetPx - Number of pixels from the viewport to start loading.
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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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yOffsetPx: number = 500,
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deps: Array<any> = []
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) {
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const [srcLoaded, setSrcLoaded] = React.useState(false);
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const threshold = 0.01;
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function calcRootMargin(value) {
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const devicePixelRatio = window.devicePixelRatio || 1.0;
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if (devicePixelRatio < 1.0) {
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return Math.ceil(value / devicePixelRatio);
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}
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return Math.ceil(value * devicePixelRatio);
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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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// $FlowFixMe
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target.src = target.dataset.src;
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setSrcLoaded(true);
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return;
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}
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// useful for lazy loading background images on divs
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if (target.dataset.backgroundImage) {
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target.style.backgroundImage = `url(${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 0px ${calcRootMargin(yOffsetPx)}px 0px`,
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threshold: [threshold],
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}
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);
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// $FlowFixMe
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lazyLoadingObserver.observe(elementRef.current);
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}, deps);
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return srcLoaded;
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}
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