Vanilla JS: Scrolling up or down

js_scrolling_direction_detection.js

let scrollPos = 0;
const Elem = document.querySelector('.element');

function checkPosition() {
	let windowY = window.scrollY;
	if (windowY < scrollPos) {
		// Scrolling UP
		Elem.classList.add('is-visible');
		Elem.classList.remove('is-hidden');
	} else {
		// Scrolling DOWN
		Elem.classList.add('is-hidden');
		Elem.classList.remove('is-visible');
	}
	scrollPos = windowY;
}

function debounce(func, wait = 10, immediate = true) {
  let timeout;
  return function() {
	let context = this, args = arguments;
	let later = function() {
	  timeout = null;
	  if (!immediate) func.apply(context, args);
	};
	let callNow = immediate && !timeout;
	clearTimeout(timeout);
	timeout = setTimeout(later, wait);
	if (callNow) func.apply(context, args);
  };
};

window.addEventListener('scroll', debounce(checkPosition));