(function(C2C) {

"use strict";

C2C.add_tooltips = function(css_class_to_observe)
{
    document.observe('dom:loaded', function(){
        $$(css_class_to_observe).each(function(obj){
            obj.observe('click', function(e){
            new Ajax.Updater('fields_tooltip',
                                    '/common/getinfo', 
                                    { asynchronous:true, 
                                      postBody: 'elt=' + obj.id,
                                      evalScripts:false, 
                                      method:'post', 
                                      onSuccess:function(request, json){
                                                        Element.hide('indicator');Element.show('fields_tooltip');
                                                        },
                                      onFailure:function(request, json){
                                                        Element.hide('indicator');
                                                        },
                                      onLoading:function(request, json){
                                                        Element.hide('fields_tooltip');Element.show('indicator');}
                                    }
                        );  
            });
        });
    });
};

})(window.C2C = window.C2C || {});

(function(C2C, $) {

  C2C.add_tooltips = function(css_class_to_observe) {
    // once dom loaded, load tooltip info via an ajax request
    // when clicking the field label
    $(function() {
      $(css_class_to_observe).click(function() {

        var indicator = $('#indicator');
        var tooltip = $('#fields_tooltip');

        tooltip.hide();
        indicator.show();

        $.post('/common/getinfo', {
          elt: this.id
        }).done(function(data) {
          indicator.hide();
          tooltip.html(data);
          tooltip.show();
        }).fail(function() {
          indicator.hide();
        });

      });
    });
  };

})(window.C2C = window.C2C || {}, jQuery);

use jquery instead of prototype