Throw an error on custom payment checkout

Question

I am writing a custom checkout module to work with the OnePage Checkout and I want a JavaScript alert to tell the user when their card has been declined or there has been an error with the API. Currently, the PHP processing throws an exception via Mage::throwException, but this does not cause a JavaScript error to pop up.

How can I do this? Is JavaScript code required, or do I need to return a specific data structure in the capture or process function?

Answer 1

Hi and welcome to Magento.SE! This is already a feature of the Magento Onepage Checkout.

In checkout any error raised (including those thrown from the gateway) are displayed as a Javascript alert. Take the current in-built Magento Authorize.net module (here shown in Sandbox mode) in the case of a decline:

It responds with a decline in a Javscript alert:

How does it do that?

If you look in the payment module for the error returned we can see that it's the description text on an Exception from Mage_Paygate_Model_Authorizenet::_place

File app/code/core/Mage/Paygate/Model/Authorizenet.php (line 519):

//line 519:
case self::REQUEST_TYPE_AUTH_CAPTURE:
    $newTransactionType = Mage_Sales_Model_Order_Payment_Transaction::TYPE_CAPTURE;
    $defaultExceptionMessage = Mage::helper('paygate')->__('Payment capturing error.');
    break;

//...
//line 576:
Mage::throwException($defaultExceptionMessage);

So - we see that any exception raised during payment place bubbles back up as a JSON response. If you look at the network tab on a failed payment submit you'll see the JSON response from the route checkout/onepage/saveOrder:

{"success":false,"error":true,"error_messages":"Payment capturing error."}

Those three properties are the key to displaying the Javascript alert:

• Success must be false
• Error must be true
• error_messages contains the text from the Mage::throwException message

To tap into this all that would be required is to throw a custom exception from your payment method