# Performing Callbacks after Form Submits (For Dev)

Occasionally, you will want custom landing page behavior to be triggered after checkout or after an upsell, but before the next page attempts to load.

This can be accomplished by assigning a callback function to a global JavaScript variable named: 'kform\_formSubmitCallback'. The signature of this callback is: 'function(response, success)', where response is the API response or error message, and success is either true for a successful transaction or false otherwise.

For example, placing the following code on your upsell page will automatically redirect the customer to the next page, even if the transaction declined, once they close the error dialog:

```
window.addEventListener('load',function()
{
    kform_formSubmitCallback = function(response, success)
    {
        if (!success)
            document.location.href = <?php echo $ksdk->redirectsTo; ?>;
    }
}
```

Additionally, you can prevent the page from automatically redirecting to the next page after a successful transaction by returning false from this callback:

```
kform_formSubmitCallback = function(response, success)
{
    return !success;
}
```

Returning anything other than false results in the Konnektive SDK continuing with normal behavior after the callback.

(i.e. Automatically redirecting on transaction success, and doing nothing after a transaction decline or error.)


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