Using JQuery to check if no radio button in a group has been checked

I'm using

$("input:radio[name='html_radio']").is(":checked")

And will return FALSE if all the items in the radiogroup are unchecked and TRUE if an item is checked.

if (!$("input[name='html_elements']:checked").val()) {
   alert('Nothing is checked!');
}
else {
  alert('One of the radio buttons is checked!');
}

if ($("input[name='html_elements']:checked").size()==0) {
   alert('Nothing is checked!');
}
else {
  alert('One of the radio buttons is checked!');
}

You could do something like this:

var radio_buttons = $("input[name='html_elements']");
if( radio_buttons.filter(':checked').length == 0){
  // None checked
} else {
  // If you need to use the result you can do so without
  // another (costly) jQuery selector call:
  var val = radio_buttons.val();
}