Edit in JSFiddle

$(document).ready(function() {
    $('#btnSort').click(function(e) {
        $("#ddlList").html($('#ddlList option').sort(function(x, y) {
            return $(x).text() < $(y).text() ? -1 : 1;
        }))
        $("#ddlList").get(0).selectedIndex = 0;
        e.preventDefault();
    });

    $('#btnSortVal').click(function(e) {
        $("#ddlList").html($('#ddlList option').sort(function(x, y) {
            return $(x).val() < $(y).val() ? -1 : 1;
        }))
        $("#ddlList").get(0).selectedIndex = 0;
        e.preventDefault();
    });
});

<select id="ddlList">
  <option value="3">Three</option>
  <option value="1">One</option>
  <option value="0">Zero</option>
  <option value="2">Two</option>
  <option value="8">Eight</option>
</select>
<br/><br/>
<input type="button" id="btnSort" Value=" Sort Dropdown By Text " />
<input type="button" id="btnSortVal" Value=" Sort Dropdown By Value " />

body
{
    padding: 10px;
    font-family:Calibri;
    font-size: 12pt;
}

input
{
    font-family:Calibri;
    font-size: 12pt;
}

select
{
    font-family:Calibri;
    font-size: 12pt;
    color: Black;
    background-color: Lightblue;
}