Magento Register Form validate with VarienForm function get response

var theForm = new VarienForm('frm_feedback', true);  

Where frm_feedback is your form id

   if (theForm.validator && theForm.validator.validate())   
   {
     // if validation successful pass then
   }
  else
  {
  //magento validation fire
   }

example:

 <form id="co-shipping-method-form" action=""> 

var theForm = new VarienForm('co-shipping-method-form', true); 

   if (theForm.validator && theForm.validator.validate())   
   {
     // if validation successful pass then
   }
  else
  {
  //magento validation fire
   }