[Javascript] IntersectionObserver -- Lazy Load Images on a Website

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When it comes to websites performance is king. How long it takes for a page to load can mean the difference of millions of dollars for large ecommerce sites. In this lesson we‘ll use the IntersectionObserver to check when an image is in the viewport to defer loading the image.

  document.addEventListener(‘DOMContentLoaded‘, () => {      const lazyImages = Array.from(document.querySelectorAll(‘img.lazy‘));      if (‘IntersectionObserver‘ in window && ‘IntersectionObserverEntry‘ in window && ‘intersectionRatio‘ in window.IntersectionObserverEntry.prototype) {          // Define the observer          let lazyImageObserver = new IntersectionObserver((entries, observer) => {              entries.forEach((entry) => {                  // logic for handling interstion                  if (entry.isIntersecting) {                      let lazyImage = entry.target                      lazyImage.src = lazyImage.dataset.src                      lazyImage.srcset = lazyImage.dataset.srcset                      lazyImage.classList.remove(‘lazy‘)                      lazyImageObserver.unobserve(lazyImage)                  }              })          })          // What to observe          lazyImages.forEach(lazyImage => {              lazyImageObserver.observe(lazyImage)          })      } else {      }  })

 

https://developer.mozilla.org/en-US/docs/Web/API/Intersection_Observer_API

https://developer.mozilla.org/en-US/docs/Web/API/Intersection_Observer_API/Timing_element_visibility

 

[Javascript] IntersectionObserver -- Lazy Load Images on a Website