How to prevent behavior-attached functions from being attached twice? I have a behavior that adds on to some checkboxes.

(function($) { 
  Drupal.behaviors.mymodule = {
    attach: function (context, settings) {

      $('.skip-line', context).on('change', function(){
        // some code
        if ( confirm(Drupal.t('Apply to all languages?')) ) {
          // applying...
        }
      });
    }
  };
})(jQuery);


It works very well, but checkboxes are in AJAX-loaded part. If I reload that part of the form, clicking on them makes confirmation popup twice. Now, I know I can test inside function if it's the first time in a row it's called, but I would prefer to make sure it is added to my element only once, and thus called only once. How can I do that?
The once() function will help with that,e.g.

(function($) { 
   Drupal.behaviors.mymodule = {
    attach: function (context, settings) {

      $('.skip-line', context).once('mymodule').on('change', function(){
        // some code
        if ( confirm(Drupal.t('Apply to all languages?')) ) {
          // applying...
        }
      });
    }
  };
})(jQuery);


One of the many references