Sticky

sticky.js

$(window)
  .on('scroll', onScroll);

function onScroll() {
  var sticky = $('.js-sticky-nav').filter(':visible');

  if (sticky.length) {
    toggleSticky(sticky);
  }
}

function toggleSticky($nav) {
  if (!$nav.hasClass('is-fixed')) {
    navOffset = $nav.offset().top;
  }

  var isFixed = $(window).scrollTop() > navOffset;

  $nav.toggleClass('is-fixed', isFixed);
}