SO fiddle

Test Fiddle mainly for SO Questions

by Nick Craver

HTML

<link rel="stylesheet" href="http://ajax.googleapis.com/ajax/libs/jqueryui/1.8.4/themes/overcast/jquery-ui.css">
<button>Toggle</button>
<div id="one">Hi! I'm div #one, how ya doin?</div>
<div id="two">I show only when one is gone</div>

CSS

div { height: 100px; bordeR: solid 1px #ddd; }
#one { display: none; }

JavaScript

$("button").toggle(function() {
    $("#two").hide();
    $("#one").slideDown();
}, function() {
    $("#one").slideUp(function() {
       $("#two").show(); 
    });
});