jQuery - Sticky header that shrinks when scrolling down

Question

I wonder how to make a sticky header shrink(with animation) when you scroll down the page and goes back to normal state when the page is scrolled up to the top. Here are two

Answer 1

I did an upgraded version of jezzipin's answer (and I'm animating padding top instead of height but you still get the point.

 /**
 * ResizeHeaderOnScroll
 *
 * @constructor
 */
var ResizeHeaderOnScroll = function()
{
    this.protocol           = window.location.protocol;
    this.domain             = window.location.host;
};

ResizeHeaderOnScroll.prototype.init    = function()
{
    if($(document).scrollTop() > 0)
    {
        $('header').data('size','big');
    } else {
        $('header').data('size','small');
    }

    ResizeHeaderOnScroll.prototype.checkScrolling();

    $(window).scroll(function(){
        ResizeHeaderOnScroll.prototype.checkScrolling();
    });
};

ResizeHeaderOnScroll.prototype.checkScrolling    = function()
{
    if($(document).scrollTop() > 0)
    {
        if($('header').data('size') == 'big')
        {
            $('header').data('size','small');
            $('header').stop().animate({
                paddingTop:'1em',
                paddingBottom:'1em'
            },200);
        }
    }
    else
      {
        if($('header').data('size') == 'small')
        {
            $('header').data('size','big');
            $('header').stop().animate({
                paddingTop:'3em'
            },200);
        }  
      }
}

$(document).ready(function(){
    var resizeHeaderOnScroll = new ResizeHeaderOnScroll();
    resizeHeaderOnScroll.init()
})