Notification alert similar to how stackoverflow functions

Question

How does stackoverflow create the slidedown effect to alert a user of a change ?

Answer 1

Stack Overflow uses the jQuery framework, which has a method to show a hidden element using a simple animation, something like:

$('#notification-bar').show('slow');

http://api.jquery.com/show/ (check out the demos).

It is fixed to the top of the page using position:fixed in CSS:

#notification-bar { 
   position:fixed;
   top: 0px; 
   left: 0px;
   width: 100%;
}

Answer 2

I think they use a timed event: jQuery Timed Event

Which sends an AJAX call to the SO severs: http://api.jquery.com/jQuery.ajax/

And then shows it in the div using the effect Andy E mentioned