function Catalog()
{
}
Catalog.categoryID = null;
Catalog.subcategoryID = null;
Catalog.productID = null;

Catalog.setup = function ()
{
    var elems = document.getElementsByTagName("select");
    for (var i = 0; i < elems.length; i++)
    {
        if (elems[i].className.match(/\bsendonchange\b/))
            elems[i].onchange = Catalog.select_onchange;

        Catalog.updateValues(elems[i]);
    }
}

Catalog.select_onchange = function ()
{
    Catalog.updateValues(this);
    Catalog.updateLocation();
}

Catalog.updateValues = function (control)
{
    if (control == null)
        return;
        
    if (control.className.match(/\bcategory\b/))
        Catalog.categoryID = control.value;
    if (control.className.match(/\bsubcategory\b/))
        Catalog.subcategoryID = control.value;
    if (control.className.match(/\bproduct\b/))
        Catalog.productID = control.value;
}

Catalog.updateLocation = function ()
{
    var prefix = "mypage.aspx?pageid=123";
    var params = new Array();
}

$(document).ready(Catalog.setup);