Event on scroll

Hi and thanks for your plugin. It works nice.

I would like it to use it only on scroll up so i wrote this code

let scrollPos = 0;
const nav = document.querySelector('.wcbb-bottom-bar');

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

window.addEventListener('scroll', checkPosition);

But it seems to not work.

Do you have any idea of how you could help me with this?
Thanks