41 lines
1.3 KiB
JavaScript
41 lines
1.3 KiB
JavaScript
// credit: https://www.sitepoint.com/five-techniques-lazy-load-images-website-performance/
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// create config object: rootMargin and threshold
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// are two properties exposed by the interface
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// more information: https://developer.mozilla.org/en-US/docs/Web/API/Intersection_Observer_API
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const config = {
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// margin around the root element defaulting to the viewport
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rootMargin: '500px 0px 500px 0px',
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// how much of the image has to be on screen to load the image
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threshold: 0
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};
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// register the config object with an instance
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// of intersectionObserver
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let observer = new IntersectionObserver(onCloseToVisibleArea, config);
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window.addEventListener("load", function () {
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const imgs = document.querySelectorAll('img[data-src]');
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imgs.forEach(img => {
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observer.observe(img);
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});
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})
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function onCloseToVisibleArea(entries, self) {
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// iterate over each entry
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entries.forEach(entry => {
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// process just the images that are intersecting.
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// isIntersecting is a property exposed by the interface
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if (entry.isIntersecting) {
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// custom function that copies the path to the img
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// from data-src to src
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preloadImage(entry.target);
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// the image is now in place, stop watching
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self.unobserve(entry.target);
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}
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});
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}
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function preloadImage(imgTag) {
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imgTag.setAttribute("src", imgTag.getAttribute("data-src"));
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} |