Affix is not working in Bootstrap 4 (alpha)

Question

According to Bootstrap 3 docs I have added following attributes to a navbar:

Answer 1

For the users who are looking for an answer in pure Javascript, this is how you can do it by using pure Javascript:

window.onscroll = (e) => {
    let scrollValue = window.scrollY;
    if (scrollValue > 120) {
        document.querySelector('.navbar').classList.add('affix');
    } else{
        document.querySelector('.navbar').classList.remove('affix');
    }
}