[jQuery] Is array empty?

Hello,
I have the folllowing:
var levels = [];
$levels = $('input[name="Levels"]:checked +
label');
levels = $levels.map(function() { return $
(this).text(); }).get();
How can I check if levels array is empty?
I tried levels, levels.val(), etc but I was not able to make this
work.
Thanks,
Miguel