[javascript] How to fix div on scroll

I made a mix of the answers here, took the code of @Julian and ideas from the others, seems clearer to me, this is what's left:

fiddle http://jsfiddle.net/wq2Ej/

jquery

//store the element
var $cache = $('.my-sticky-element');

//store the initial position of the element
var vTop = $cache.offset().top - parseFloat($cache.css('marginTop').replace(/auto/, 0));
  $(window).scroll(function (event) {
    // what the y position of the scroll is
    var y = $(this).scrollTop();

    // whether that's below the form
    if (y >= vTop) {
      // if so, ad the fixed class
      $cache.addClass('stuck');
    } else {
      // otherwise remove it
      $cache.removeClass('stuck');
    }
  });

css:

.my-sticky-element.stuck {
    position:fixed;
    top:0;
    box-shadow:0 2px 4px rgba(0, 0, 0, .3);
}