mdbootstrap4-pro/js/modules/vendor/scrolling-navbar.js

MDBootstrap 4 PRO

/* SCROLLING NAVBAR */
const OFFSET_TOP = 50

$(window).scroll(() => {
  if ($('.navbar').offset().top > OFFSET_TOP) {
    $('.scrolling-navbar').addClass('top-nav-collapse')
  } else {
    $('.scrolling-navbar').removeClass('top-nav-collapse')
  }
})