Add plus and minus buttons to WPForms "Single Item" field quantity selector

wpforms_maybe_insert_single_item_controls.php

<?php
// Insert Plus and Minus buttons on eligible Single Item fields.
function wpforms_maybe_insert_single_item_controls() {
?>
<script type="text/javascript">
  const select = document.querySelector('.wpforms-insert-single-item-controls select');

  function getSelector(direction) {
    return (event) => {
      event.preventDefault();
      event.stopPropagation();
      const min = Number(select[0].value);
      const max = Number(select[select.length - 1].value);
      jQuery(select)
        .val(Math.max(min, Math.min(max, Number(jQuery(select).val()) + direction)))
        .trigger('change');
    };
  }

  const minusButton = document.createElement('button');
  minusButton.classList.add('wpforms-single-item-control', 'wpforms-single-item-control-minus');
  minusButton.textContent = '-';
  minusButton.addEventListener('click', getSelector(-1));
  select.insertAdjacentElement('beforebegin', minusButton);

  const plusButton = document.createElement('button');
  plusButton.classList.add('wpforms-single-item-control', 'wpforms-single-item-control-plus');
  plusButton.textContent = '+';
  plusButton.addEventListener('click', getSelector(1));
  select.insertAdjacentElement('afterend', plusButton);
</script>
<?php
}
add_action('wpforms_wp_footer_end', 'wpforms_maybe_insert_single_item_controls', 30);

I used WPCode to add this PHP snippet as a shortcode. Then I placed the shortcode on the page with the WPForms form that I wanted to apply this to.

You also need to add wpforms-insert-single-item-controls as a custom class on the field you want it to add the controls to.

Note, as written it will only apply this to the first Single Item field with the custom class applied. The code could be modified to just use querySelectorAll, loop over the results, and apply the treatment to all instances.