onchange event for html.dropdownlist

If you don’t want jquery then you can do it with javascript :-

@Html.DropDownList("Sortby", new SelectListItem[] 
{ 
     new SelectListItem() { Text = "Newest to Oldest", Value = "0" }, 
     new SelectListItem() { Text = "Oldest to Newest", Value = "1" },
     new { @onchange="callChangefunc(this.value)" } 
});

<script>
    function callChangefunc(val){
        window.location.href = "/Controller/ActionMethod?value=" + val;
    }
</script>