Smart scroll

basic.html

<nav class="navbar smart-scroll navbar-expand-lg navbar-dark bg-primary">
  <a class="navbar-brand" href="#">Brand</a>
  <button class="navbar-toggler" type="button" data-toggle="collapse" data-target="#main_nav" aria-expanded="false" aria-label="Toggle navigation">
    <span class="navbar-toggler-icon"></span>
  </button>
  <div class="collapse navbar-collapse" id="main_nav">
    <ul class="navbar-nav">
      <li class="nav-item active"> <a class="nav-link" href="#">Home </a> </li>
      <li class="nav-item"><a class="nav-link" href="#"> About </a></li>
      <li class="nav-item"><a class="nav-link" href="#"> Services </a></li>
    </ul>
  </div> <!-- navbar-collapse.// -->
</nav>

script.js

// add padding top to show content behind navbar
$('body').css('padding-top', $('.navbar').outerHeight() + 'px')

// detect scroll top or down
if ($('.smart-scroll').length > 0) { // check if element exists
    var last_scroll_top = 0;
    $(window).on('scroll', function() {
        scroll_top = $(this).scrollTop();
        if(scroll_top < last_scroll_top) {
            $('.smart-scroll').removeClass('scrolled-down').addClass('scrolled-up');
        }
        else {
            $('.smart-scroll').removeClass('scrolled-up').addClass('scrolled-down');
        }
        last_scroll_top = scroll_top;
    });
}

style.css

.smart-scroll{
  position: fixed;
  top: 0;
  right: 0;
  left: 0;
  z-index: 1030;
}
.scrolled-down{
   transform:translateY(-100%); transition: all 0.3s ease-in-out;
}
.scrolled-up{
   transform:translateY(0); transition: all 0.3s ease-in-out;
}