Add object routedValue in Confirmation dialog of a Ajax.BeginForm

Question

What I want is to add an object routed value when the user submits the form (ajax.beginform)

Depending on what the user chooses in the ConfirmDone function, i want to add an integer (SaveOption)

But i don't really know how to do it.

The confirmdone function is called but that's it, my controller action is'nt called. I probably need to return something?

Some Code: the start of the form

@using (Ajax.BeginForm("CreateFunctiebeschrijvingPartial", "Functiebeschrijving", new     AjaxOptions { UpdateTargetId = "Functiebeschrijving", OnBegin = "return ConfirmDone()", OnSuccess = "handleSuccess" }, new {@id = frmID}))
{

The confirmdone function

function ConfirmDone() {
    if (confirm("This form saves default as Concept, would you like to save it as completed? 1 = Completed, 2 = Concept")) {
        //option 1: save as completed
        $('#frmID').attr("SaveOption", 1);                        
    }
    else {
        //Option 2: save as concept
    }
}

The start of my controller action

//
// POST: /FunctieBeschrijving/CreateFunctiebeschrijvingPartial
[HttpPost]
public ActionResult CreateFunctiebeschrijvingPartial(NieuweFunctiebeschrijvingViewModel nfvm, int SaveOption)
{

When i don't use the confirm function, everything is posted as it should be!

Answer 1

function addDataToUrl(url, name, value){
    var sep = url.indexOf('?') === -1 ? '?' : '&';
    return url + sep + name + '=' + value;   
}

function ConfirmDone() {
    var form = document.getElementById('frmID');
    if (confirm("This form saves default as Concept, would you like to save it as completed? 1 = Completed, 2 = Concept")) {
        //option 1: save as completed
        form.setAttribute('action', 
        addDataToUrl(form.getAttribute('action'), 'SaveOption', '1'));                   
    }
    else {
        // Option 2: save as concept
    }
}