$("#item").removeClass();
Calling removeClass
with no parameters will remove all of the item's classes.
You can also use (but it is not necessarily recommended. The correct way is the one above):
$("#item").removeAttr('class');
$("#item").attr('class', '');
$('#item')[0].className = '';
If you didn't have jQuery, then this would be pretty much your only option:
document.getElementById('item').className = '';
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