onEmptinessChange Callback
The onEmptinessChange( ) callback method is invoked when the hosted field becomes empty or is no longer empty.
Usage
PaymentSession.onEmptinessChange([HostedFieldsRole], function(selector, result), [scope])
Example
PaymentSession.onEmptinessChange(["card.number", "card.nameOnCard"], function(selector, result) {
    //handle change event
    if (result.isEmpty) {
        // field has empty value
        console.log("Element with selector " + selector + " has changed it's emptiness status to empty");
    } else if (!result.isEmpty) {
        // field has non-empty value
        console.log("Element with selector " + selector + " has changed it's emptiness status to non-empty");
    }
});
    Example for emptiness change result object
{
    "isEmpty":boolean
}
Arguments
An array of field roles for the hosted fields where the event occurred. Valid array of field roles:
card.nameOnCard
            card.number
            card.expiryMonth
            card.expiryYear
            card.securityCode
            giftCard.number
            giftCard.pin
            ach.bankAccountNumber
            ach.bankAccountNumberConfirmation
            ach.bankAccountHolder
            ach.routingNumber
            directDebitCanada.bankAccountNumberConfirmation
            directDebitCanada.bankAccountHolder
            directDebitCanada.bankAccountNumber
            directDebitCanada.financialInstitutionNumber
            directDebitCanada.transitNumber
            The callback function invoked with selector and the result when an event is triggered.
Identifier of the HTML element that the merchant has changed the state of emptiness (ex: "#card-number").
Result object which sent as an argument to the function.
It defines whether that particular field is empty or not.
The optional named instance of a card payment data set within a session. See Multiple Hosted Sessions for more information.
Return Value
None