accesing all radcombobox in javascript and changing css style

Question

i am writing a Javascript to access all my radcombobox and changing to the default skin .I tried the following script but its not working .

   for (var i in errorControls) {
       var element = errorControls[i];
       if (Telerik.Web.UI.RadComboBox && element instanceof Telerik.Web.UI.RadComboBox) {
            element.className  = "RadComboBox_default";
            }
            else {
             element.className = "ErrorControl";
            }
   }