Navigation dropdown on page scroll

nav-dropdown-on-scroll.js

openDropdownNav = function() {
  return $('header').addClass('dropdown-nav').slideDown();
};
closeDropdownNav = function() {
  return $('header.dropdown-nav').slideUp(function() {
    return $('header').removeClass('dropdown-nav').stop().removeAttr('style');
  });
};
getDocHeight = function() {
  var D;
  D = document;
  return Math.max(D.body.scrollHeight, D.documentElement.scrollHeight, D.body.offsetHeight, D.documentElement.offsetHeight, D.body.clientHeight, D.documentElement.clientHeight);
};
lastScroll = 0;
$(window).bind('scroll', function() {
  var bottom, currentScroll, pastFirstFrame, top;
  currentScroll = $(this).scrollTop();
  pastFirstFrame = currentScroll > $('#front, #about-header, body.services #sanky-divisions, #work-header, .work-sample-header, .blog-header').height();
  top = currentScroll <= 150;
  bottom = currentScroll + window.innerHeight >= getDocHeight() - 100;
  if (bottom) {
    openDropdownNav();
  }
  if (top && $('header.dropdown-nav').is(':visible')) {
    closeDropdownNav();
  }
  if (!bottom) {
    if (currentScroll > lastScroll && $('header.dropdown-nav').is(':visible')) {
      closeDropdownNav();
    }
  }
  if (currentScroll < lastScroll && pastFirstFrame) {
    openDropdownNav();
  }
  return lastScroll = currentScroll;
});