Detect scroll distance from top and/or bottom and scroll up and down.

detect-scroll.js

/**
 * Detect Scroll.
 *
 * Detect scroll distance from top and/or bottom and scroll up and down.
 */
( function( $ ) {

	var lastScrollTop = 0, delta = 20;

	$(window).scroll(function(){

		// Distance from top.
		if ( $( this ).scrollTop() > 500 ) {
			$( "#top-bar" ).addClass( "foo" );
		} else {
			$( "#top-bar" ).removeClass( "foo" );
		}

		// Distance from top and distance from bottom.
		if ( $( this ).scrollTop() > 500 && $( this ).scrollTop() + $( this ).height() < $(document).height() - 500 ) {
			$( "#top-bar" ).addClass( "bar" );
		} else {
			$( "#top-bar" ).removeClass( "bar" );
		}

		// Detect scroll up and down.
		var nowScrollTop = $(this).scrollTop();

		if ( Math.abs( lastScrollTop - nowScrollTop ) >= delta ) {
			if ( nowScrollTop > lastScrollTop ) {
				$( "#top-bar" ).addClass( "flob" );
			} else {
				$( "#top-bar" ).removeClass( "flob" );
			}
			lastScrollTop = nowScrollTop;
		}
	});

})( jQuery );