Detect scroll direction

var lastScrollTop = 0;
$(window).scroll(function(event) {
  var st = $(this).scrollTop();
  if (st > lastScrollTop) {
    //Scroll Down
  }
  else if (st == lastScrollTop) {
    //do nothing 
    //In IE this is an important condition because there seems to be some instances where the last scrollTop is equal to the new one
  }
  else {
    //Scroll Up
  }
  lastScrollTop = st;
});