Issue with AJAX Add to Cart Button in Magento 1.9

So I came up with a solution that works just awesome. I added another controller action and a model to do the Magento Interactions during my ajax calls. So let me show you how it's done, I hope somebody can profit from this sooner or later :)

My new Action:

public function updateAction ()
   {

      //Instantiate Product Model
      $productModel = Mage::getModel('doorconfig/product');

      //Get Updated Values from the Model
      $currentProduct = $productModel->getProduct($_POST);
      $currentProductId = $currentProduct->getId();
      $currentProductUrl = $currentProduct->getProductUrl();
      $currentPrice = $productModel->getPrice($currentProductId);
      $currentType = $this->getRequest()->getPost('doorconfig_type');
      $currentSize = $this->getRequest()->getPost('doorconfig_size');
      $currentProductBaseImgUrl = $productModel->getDoorBaseImgUrl($currentType,$currentSize);

      //Populate Resultarray
      $result = array("currentProductId"=>$currentProductId,"currentPrice"=>$currentPrice,"currentProductUrl"=>$currentProductUrl,"currentProductBaseImgUrl"=>$currentProductBaseImgUrl);

      //Encode Result in JSON
      $this->getResponse()->setBody(Mage::helper('core')->jsonEncode($result));

      return $result;
   }

My model just got most of the business logic from my block, so nothing special to point out about that.

And finally the updated Ajax section which now triggers my new controller action, receives the result as a JSON encode and changes the values in the DOM:

<script type="text/javascript">

   var $price = "";
   var $baseImgUrl = "";
   var $productUrl = "";
   var $productId = "";
   var $f = $j("#attributeform");
    var $formData;
    var $currentStoreUrl = "<?php echo $currentStoreUrl ?>";

   function ajaxUpdate()
   {

      $j.ajax({
         url: "/doorconfig/index/update",
         type: "POST",
         data: $formData,
         dataType: "json",
         success: function(data) 
                {
                  $productId = data.currentProductId;
                  $price = data.currentPrice;
                  $baseImgUrl = data.currentProductBaseImgUrl;
                  $productUrl = data.currentProductUrl;
                     $j("#result").text($price);

                     $j("#addtocart").attr('href',  $currentStoreUrl + "checkout/cart/add?product=" + $productId + "&qty=1");
                     $j("#productimg").attr('src', $baseImgUrl);

                     console.log(data);

                   },
            error: function(error)
                  {
                     console.log("Error:");
                     console.log(error);
                     alert("ERROR");
                  }
        });
    };

   $j(document).ready(function() 
   {

      $j("#result").text('<?php echo $defaultProductPrice; ?>');
      $j("#addtocart").attr('href', '<?php  echo $currentStoreUrl . "checkout/cart/add?product=" . $defaultProductId . "&qty=1" ?>');
      $j("#moreinfo").attr('href', '<?php echo $defaultProductUrl; ?>');
      $j("#productimg").attr('src', '<?php echo $defaultProductImgUrl; ?>');
      $j("#attributeform")[0].reset();

      $j("form[name=attributeform]").change(function () 
      {

         $formData = $f.serialize();
         ajaxUpdate();
      })
   });   

</script>

If you need any further explanation or wanna improve something please comment :)

I've not had chance to test the code, but I'd guess the issue with not adding products to the basket (i.e. empty cart) is due to Magento 1.8 introducing the FORMKEY element. (see https://stackoverflow.com/questions/19153691/magento-add-a-product-to-the-cart-via-query-string-without-form-key-parameter). Looks like you can get the form key from the session:

Mage::getSingleton('core/session')->getFormKey();