How to put this Javascript function return in a HiddenField c# object?

Question

I need to put the return of the function validarCartao() into that HiddenField value. The alert(response.brand.name) works fine but I cant get this, even if I move the HiddenField to inside the function. I've tried lots of ways but nothing works. I really appreciate any help you can provide. Thanks.

var hiddenBandeiraTemp = document.getElementById('<%=hiddenBandeira.ClientID%>');

hiddenBandeiraTemp.value = validarCartao(tbNumeroCartao.value);

function validarCartao(element) {

            var cardNum = element.replace(/[^\d.]/g, '');
            var card_invalid = 'Número do cartão inválido.';

            if (cardNum.length >= 6) {
                PagSeguroDirectPayment.getBrand({
                    cardBin: cardNum.substr(0, 6),
                    success: function (response) {
                        if (typeof response.brand.name != 'undefined') {
                            alert(response.brand.name); // OK
                            return response.brand.name; // <<--
                        } else {
                            alert(card_invalid);
                        }
                    },
                    error: function (response) {
                        alert(card_invalid);
                    }
                });
            }
        }

Answer 1

The return statement that you put inside the success callback will return a value for the function success() not for the function validarCartao()

success: function (response) {
    if (typeof response.brand.name != 'undefined') {
        alert(response.brand.name); // OK
        return response.brand.name; // <<--
    } else {
        alert(card_invalid);
    }
}

Moreover, as the function PagSeguroDirectPayment.getBrand() seems to be asynchronous, it is impossible to return its value inside validarCartao(). In my opinion, this would be a better solution:

var hiddenCompradorIdTemp = document.getElementById('<%=hiddenCompradorId.ClientID%>');

validarCartao(tbNumeroCartao.value);

function validarCartao(element) {

            var cardNum = element.replace(/[^\d.]/g, '');
            var card_invalid = 'Número do cartão inválido.';

            if (cardNum.length >= 6) {
                PagSeguroDirectPayment.getBrand({
                    cardBin: cardNum.substr(0, 6),
                    success: function (response) {
                        if (typeof response.brand.name != 'undefined') {
                            alert(response.brand.name); // OK
                            hiddenBandeiraTemp.value = response.brand.name;
                        } else {
                            alert(card_invalid);
                        }
                    },
                    error: function (response) {
                        alert(card_invalid);
                    }
                });
            }
        }