Доступ isvalid свойство блоков проверки допустимости ASP.NET в JavaScript

I don't think the isvalid works on a validator control directly as this is a server side validation function. You can fire a validator check for the current page or validation group using the client side javascript function Page_ClientValidate. You can optionally specify a validation group name a parameter. This will return true if all the validation passes.

You can also look at more available client-side functions and how they map to the server side functions on MSDN at:

http://msdn.microsoft.com/en-us/library/yb52a4x0.aspx