website-11ty-kogakure.de/src/assets/scripts/modules/scroll-handler.js

export function scrollHandler() {
	const body = document.body;
	const scrollUp = 'scroll-up';
	const scrollDown = 'scroll-down';
	let lastScroll = 0;

	window.addEventListener('scroll', () => {
		const currentScroll = window.pageYOffset;

		if (currentScroll <= 0) {
			body.classList.remove(scrollUp);
			return;
		}

		if (currentScroll > lastScroll && !body.classList.contains(scrollDown)) {
			body.classList.remove(scrollUp);
			body.classList.add(scrollDown);
		} else if (currentScroll < lastScroll && body.classList.contains(scrollDown)) {
			body.classList.remove(scrollDown);
			body.classList.add(scrollUp);
		}
		lastScroll = currentScroll;
	});
}