Add Custom Javascript

I’m trying to add custom JS to my website.
something like:
if (st > lastScrollTop && st > navbarHeight){
// Scroll Down
$(‘header’).removeClass(‘nav-down’).addClass(‘nav-up’);
} else {
// Scroll Up
if(st + $(window).height() < $(document).height()) {
$(‘header’).removeClass(‘nav-up’).addClass(‘nav-down’);

What i want to do is to add a new class to the header and remove it.
But it doesn’t work. Does Elementor block custom JS?