How to capture cmd + enter event in jquery

I need to determine when a user presses cmd+enter after typing a text into a textarea. I'm using jquery.

Here's what I tried:

<textarea id="checkMetaKey"></textarea>
<div id="display"></div>

$( "#checkMetaKey" ).keyup(function( event ) {
  $( "#display" ).text(event.metaKey + " " + event.keyCode);
});

JSFiddle: http://jsfiddle.net/WQG2b/

I would expect that to display "true 13" when cmd+enter is clicked. It's not the case however.

The only way I can get metaKey to be true is when I click CMD only or CMD+ALT or CMD+CTRL.

How do I capture a CMD+ENTER event?

Similar functionality seems to be working when I try it on Facebook, I'm able to submit message text using CMD+ENTER.