Check each element in a nested structure (like a slider) for a specific data attribute and mark these elements visually witha red background (Q&D)

data_attribute_checker.js

$('.my-outer-container').find('.my-element').each(function() {
  if(typeof $(this).data('my-datakey') === 'undefined') {
    $(this).css('background', '#FF0000');
  }
});