The trick is that you have to set it as position:fixed, but only after the user has scrolled past it.
This is done with something like this, attaching a handler to the window.scroll event
// Cache selectors outside callback for performance.
var $window = $(window),
$stickyEl = $('#the-sticky-div'),
elTop = $stickyEl.offset().top;
$window.scroll(function() {
$stickyEl.toggleClass('sticky', $window.scrollTop() > elTop);
});
This simply adds a sticky
CSS class when the page has scrolled past it, and removes the class when it’s back up.
And the CSS class looks like this
#the-sticky-div.sticky {
position: fixed;
top: 0;
}
EDIT- Modified code to cache jQuery objects, faster now.