How to activate the Bootstrap modal-backdrop?

I want to put up an overlay on my screen while some ajax stuff is running. Building my own overlay div isn't a big deal, but, since I'm already using Bootstrap, I figure I might as well use its .modal-backdrop -- it should already be around, and there's some value to consistency and all that.

The problem is I can't find the right way to do it -- I've tried adding classes to .modal-backdrop, or calling .show() on it, but it's not working.

Note that I don't want to bring up a whole modal dialog, but just reveal and then hide the backdrop.

Any suggestions?

Solution

Just append a div with that class to body, then remove it when you're done:

// Show the backdrop
$('<div class="modal-backdrop"></div>').appendTo(document.body);

// Remove it (later)
$(".modal-backdrop").remove();

Live Example:

$("input").click(function() {
  var bd = $('<div class="modal-backdrop"></div>');
  bd.appendTo(document.body);
  setTimeout(function() {
    bd.remove();
  }, 2000);
});

<link href="//netdna.bootstrapcdn.com/twitter-bootstrap/2.3.2/css/bootstrap-combined.min.css" rel="stylesheet" type="text/css" />
<script src="//code.jquery.com/jquery.min.js"></script>
<script src="//netdna.bootstrapcdn.com/twitter-bootstrap/2.3.2/js/bootstrap.min.js"></script>
<p>Click the button to get the backdrop for two seconds.</p>
<input type="button" value="Click Me">