Lazy load images with IntersectionObserver

lazyLoadImages.js

if(window.IntersectionObserver){
	const observe = function (entries, observer) {
        entries.forEach(function(entry) {
            if(entry.isIntersecting) {
                const img = entry.target
                const src = img.dataset.src
                const srcset = img.dataset.srcset

                requestIdleCallback(function () {
                    if(srcset) {
                        img.srcset = srcset
                    }
                    img.src = src
                })
                observer.unobserve(img)
            }
        })
    }

    const observer = new IntersectionObserver(observe, {})
    const images = document.querySelectorAll('img.lazy')
    images.forEach(function(img) {
        observer.observe(img)
    })
}
else {
	const images = document.querySelectorAll('img.lazy')
	for(let i=0 ; i < images.length; i++){
		const img = images[i]
		const src = img.dataset.src
		const srcset = img.dataset.srcset

		if(srcset) {
			img.srcset = srcset
		}
		img.src = src
	}
}