Sticky panel with Intersection Observer and position fixed. Add class if parent is offscreen

sticky.js

const sticky = function (panelsClass, elementsClass) {
	const panels = document.querySelectorAll('.' + panelsClass);

	const config = {
		rootMargin: '150px 20px 75px 30px',
		threshold: [0, 0.25, 0.75, 1]
	};

	const observer = new IntersectionObserver((entries) => {
		entries.forEach(entry => {
			let element = entry.target.querySelector('.' + elementsClass);
			let nextSibling = entry.target.nextSibling.nextElementSibling;
			let elHeight = element.clientHeight;
			console.log(nextSibling);

			if (entry.intersectionRatio > 0) {
				element.classList.remove('is-sticky');
				nextSibling.style.marginTop = '0';
			} else {
				element.classList.add('is-sticky');
				nextSibling.style.marginTop = elHeight + 'px'; // prevent jumping
			}
		});
	});

	panels.forEach(panel => {
		observer.observe(panel);
	}, config);
};

export default sticky