OpenCart: how to increase the quantity of a product by a multiple of the minimum in the product card?

Question

opencart

Actually, subject. Wholesale store, sold only in boxes, with a clear number of items in each box.
For OpenCart, there is the Simple module, which does an excellent job, but only with a check-out (purchase confirmation: +/- number of products is also possible on this page).

Answer 1

The issue was resolved by the code:
HTML:

<button class="counter counter-minus material-design-horizontal39" href='#'></button>
<input type="text" data-minimum="<?php echo $minimum; ?>" name="quantity" size="3" value="<?php echo $minimum; ?>" />
<input type="hidden" name="product_id" value="<?php echo $product_id; ?>"/>
<button class="counter counter-plus material-design-add186" href='#'></button>

jQuery:

;(function ($) {
    $(document).on('click', '.counter-minus, .counter-plus', function(e) {
        e.preventDefault();
    
        var input = $(this).parent().find('input[name*="quantity"]'),
        value = 1;
    
        var minimum = $(input).data('minimum');
    
        if ($(this).hasClass('counter-minus') && input.val() > minimum) {
            value = parseInt(input.val()) - minimum;
        } else if ($(this).hasClass('counter-plus')) {
            value = parseInt(input.val()) + minimum;
        }
        input.val(value);
    });
})(jQuery);

(When copying, be careful not to capture extra BOM characters)

Answer 2

In simplecheckout.js, see the increaseProductQuantity and decreaseProductQuantity functions.
As far as I can see, it adds / subtracts a multiple of the minimum amount.

Answer 3

Change
input type="text"
to
input type="number" in the code
and add
min="<?php echo $minimum; ?>" step="<?php echo $minimum; ?>"