ASP Controll Values to Javascript

I am new to web design.
I have created a dropdownlist and a readiobuttonlist. The dropdown list gets a list of names from a SQLdatasource. What I want to do is have the user select the option from the radiobuttonlist, then select the dropdownlist item, then click a button to load the appropriate (already created) web page.
I understand that launching a new window is a client side action. Am I able to refer to the server-side asp dropdownlist and get those values? Or do I need to 'pass' those values to the javascript?
I seem to be having trouble referencing the controls from the following java script code:
function fnGetRptUrl() {
        var vSort = RadioButtonList1.SelectedIndex.Value;
        var vLocationchoice = DropDownList1.SelectedItem.Value;
        var vMidValue = vSort & "/" & ...