jQuery function that identifies page scrolling direction. Used when it's needed to apply different functionality for different (up/down) scrolling directions.

jquery.scrollDirection.js

// Variable that is going to hold previous 'document' scrollTop
// value (/vertical scrollbars position).
var prevScrollTop;


// Function that returns 'true' (/boolen) if user scrolls the
// page up, 'false' (/boolen) if user scrolls the page down.
function scrollsUp(scrollTop) {
  var before = prevScrollTop;
  
  // Storing current 'document' scrollTop value.
  prevScrollTop = scrollTop;
  
  return scrollTop < before;
}


// Listening to 'window' scroll event.
$(window).on('scroll', function() {
  // Getting current 'document' scrollTop value.
  var scrollTop = $(document).scrollTop();
  
  if (scrollsUp(scrollTop)) {
    // User scrolls the page up.
    
  } else {
    // Otherwise, user scrolls the page down.
  }
});