How to do an action after an AJAX call is done?

I try to call a function at different place. That why i return true or false. Problem i got is before hasCreditCard has time to do is call, that go directly to the else...

if (hasCreditCard($('#memberId').val())) {
  ...
}
else{
  ...
}

function hasCreditCard(memberId) {
    var url = getHostName() + "/members/" + memberId + "/creditcard";
    jQuery.ajax({
        type: "head",
        url: url,
        contentType: "application/json",
        headers: {
            "Authorization": "Basic " + $.cookie('authorization')
        },
        success: function (data, status, jqXHR) {
            if (jqXHR.status == 200) {
                return true;
            }
            return false;
        },
        error: function (jqXHR, status) {
            return false;
        }
    });
}