var myGlobalHandlers = {
  onCreate: function(){
    Element.show('systemWorking');
  },

  onComplete: function() {
    if(Ajax.activeRequestCount == 0){
      Element.hide('systemWorking');
    }
  }
};

Ajax.Responders.register(myGlobalHandlers);

function reportError(t) {
    alert('Error ' + request.status + ' -- ' + request.statusText);
}

function salvaEmail() {
  var operation = 'salvaEmail';
  var url = 'ajax_operations.php';
  var params = 'operation='+operation+
               '&Newsletter__email='+$F('Newsletter__email');
  var ajax = new Ajax.Request(
                        url,
                        {
                          method: 'post',
                          parameters: params,
                          onFailure: reportError,
                          onComplete: function (transport) {
                            alert(transport.responseText);
                          }
                        });
}