Sticky navigation on scrolldown

let navbar = document.getElementById('navbar');
let mainpos = document.getElementById('main');
let navPos = mainpos.getBoundingClientRect().top;
window.addEventListener('scroll', e => {
    let scrollPos = window.scrollY;
    if (scrollPos > navPos) {
      navbar.classList.add('sticky');
    } else {
      navbar.classList.remove('sticky');
    }
  });