session value is undefined in javascript

Solved
I am using mysession.value but it solve using .tostring()

 window.onload = function () {


        var mySessionVar = '<%#Session("lnUserID")%>';
     
        alert(mySessionVar.toString());

    }

Thanks for reply

HI khargesh rajput,
as i think "The session is a server side thing.  you cannot access it using java scripts directly. You can write an Http handler (that will share the sessionid if any) and return the value from there using $.ajax or java scripts"
so what u r doing is only correct.

whenever i try <%=ffdsf%>  means = instead of #
it gives
The Controls collection cannot be modified because the control contains code blocks (i.e. <% ... %>).

error