How to adapt OpenCart 1.X code to OpenCart 2.3?

Question

opencart

The code for the "Show more" button is laid out for version 1.x, you need to adjust it for 2.3
In the file catalog/controller/product/category.php, after $product_total = $this->model_catalog_product->getTotalProducts($filter_data); add: I changed this to $data['ttl'] In catalog/view/theme/default/template/product/category.tpl, before echo $pagination; add:
$this->data['ttl'] = $product_total;

<?php if($ttl > count($products)){ ?>
  <input type="hidden" value="<?php echo $this->config->get('config_catalog_limit') + count($products); ?>" name="limit" id="pagin_limit">
  <?php if(($ttl - count($products)) >= $this->config->get('config_catalog_limit')){ ?>
    <div class="category_load">Показать еще <?php echo $this->config->get('config_catalog_limit'); ?></div>
  <?php }else{ ?>
    <div class="category_load">Показать еще <?php echo $ttl-count($products); ?></div>
  <?php } ?>
  <script>
    $(".category_load").on("click", function(){
      product_div = '.products';
      lim = $("#pagin_limit").val();
      $("." + product_div).load('index.php?route=product/category&path=<?php echo $this->request->get['path']; ?>&limit=' + lim + ' ' + product_div + '>*', function(){
        $("#pagin_limit").val(lim);
      });
    });
  </script>
<?php } ?>

Source:
https://for-opencart.com/utility/button-more
Question:
I changed only $data, but it doesn't work, what else needs to be done?

Answer 1

I haven’t picked up opencart for a long time ((
1) You need to debug (it’s good if x-debug is installed and configured), if not, then the good old var_dump(); die;
2) find out what $product_total comes in (see point 1) there should be the number of products
3) by clicking on the button, an ajax request should be called in the console, you need to make sure that it happens and there are no js errors. Next, you need to check the status of the response, whether there is a corresponding action to which the request is sent.
just as embarrassing

product_div = '.products';
....
      $("." + product_div)

according to the idea, there should be maybe
two points, this is probably overkill
and then look in stages