How to make div follow scrolling smoothly with jQuery?

Question

In my container there are sections/boxes, but the last one of these boxes should follow scrolling when none of the other boxes are visible.

So, when user sc

Answer 1

Since this question is getting a lot of views and the tutorial linked in the most voted answer appears to be offline, I took the time to clean up this script.

See it live here: JSFiddle

JavaScript:

(function($) {
    var element = $('.follow-scroll'),
        originalY = element.offset().top;

    // Space between element and top of screen (when scrolling)
    var topMargin = 20;

    // Should probably be set in CSS; but here just for emphasis
    element.css('position', 'relative');

    $(window).on('scroll', function(event) {
        var scrollTop = $(window).scrollTop();

        element.stop(false, false).animate({
            top: scrollTop < originalY
                    ? 0
                    : scrollTop - originalY + topMargin
        }, 300);
    });
})(jQuery);