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HTML

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CSS

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JavaScript

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Babel includes JSX processing.

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HTML 

              
                .slide.slide--intro
	h1 Intersection Observer Demo
	p (scroll please)

.slide
	.box.box--spin
		span Spin
	
.slide
	.box.box--grow
		span Grow
	
.slide
	.box.box--move-right
		span Move Right
!

CSS 

              
                .slide
	display flex
	align-items center
	justify-content center

	min-height 100vh
	
.slide--intro
	flex-direction column
	
.box
	display flex
	align-items center
	justify-content center
	
	width 150px
	height 150px
	
	color white
	text-align center
	
	background-color DeepPink
	transition transform 1s ease-in
	
.box--spin.box--visible
	transform rotate(1080deg)
	
.box--grow.box--visible
	transform scale(1.5)
	
.box--move-right.box--visible
	transform translateX(50px)
!

JS 

              
                // callback function to do animations
const scrollImations = (entries, observer) => {
	entries.forEach((entry) => {
		// only do animation if the element is fully on screen
		if(entry.isIntersecting && entry.intersectionRatio == 1) {
			entry.target.classList.add('box--visible');
		} else {
			entry.target.classList.remove('box--visible');
		}
	});
}

// create the observer
const options = {
	threshold: 1.0,
};
const observer = new IntersectionObserver(scrollImations, options);

// target the elements to be observed
const boxes = document.querySelectorAll('.box');
boxes.forEach((box) => {
	observer.observe(box);
});
!
999px

Console