code: function() {
          var me = this,
              valid = !me.hasInvalidField();
          if (valid !== me.wasValid) {
              me.onValidityChange(valid);
              me.fireEvent('validitychange', me, valid);
              me.wasValid = valid;
          }
      }
docs: Check whether the validity of the entire form has changed since it was last checked, and
  if so fire the {@link #validitychange validitychange} event. This is automatically invoked
  when an individual field's validity changes.