Test before save

I don't want to write a server code if I can do the same at the client side.
Here is the test for INN field, that must contain only the numbers.

var re = new RegExp("[^0-9]");
if(crmForm.all.new_inn.DataValue != null){
   if(re.test(crmForm.all.new_inn.DataValue == true){
      alert("ИНН должен содержать только цифры");
      event.returnValue = false;
      return false;
   }
}