toggleClass Fade effect not working with display:none/block.

toggleClass Fade effect not working with display:none/block.

$('.item a').click(function() {
    $('.mydiv').toggleClass('displayit', 5000);
});

So I've created div with display: none, and jquery that adds display:block (.displayit) when I click on .item a (link). Now, I want to  add fadein and out to toggleClass but it's not working. I added jquery-ui.js and it still does not work.