Affix is not working in Bootstrap 4 (alpha)

Question

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

Answer 1

simple use class fixed-top in bootstrap 4 and use addClass and removeClass

$(window).on('scroll', function(event) {
    var scrollValue = $(window).scrollTop();
    if ( scrollValue > 70) {
         $('.navbar-sticky').addClass('fixed-top');
    }else{
       $('.navbar-sticky').removeClass('fixed-top');
    }
});