Count the number of friends you've selected in a FB inviter

count_friends.js

function updateTotalSelected(form) {
  var totalSelected = getTotalSelected(form);
  var elem = getElementsByClassName(form, 'current_selected', 'span')[0];    
  elem.setTextValue(totalSelected)
}
function getTotalSelected(form) {
  var serializedForm = form.serialize();
  var ids = serializedForm.ids;
  if (!ids) {
    return 0;
  }
  var totalSelected = 0;
  for (var i in ids) {
    totalSelected++;
  }
  return totalSelected;
}

usage.html

  <fb:request-form type="cause" invite="true"
      onclick="updateTotalSelected(this)" ...>