<label id="myLabel">Select a fruit:</label>
<select id="fruitSelector">
    <option val="">None</option>
    <option val="apple">apple</option>
    <option val="orange">orange</option>
    <option val="mango">mango</option>
</select>

$("#fruitSelector").change(function(){
    $("#myLabel").text("Fruit has been selected");
});

@Html.DropDownList("State", ViewBag.StateName as SelectList,
"Select a State",
 new { id = "State" })

<label id="lbl1"></label>

<script type="text/jscript">
    $(function () {
        $('#State').change(function () {
            $('#lbl1').text($('#State').val());
        });
    });
</script>

<label id="item">Selected Item: </label>
<select id="selector">
    <option value="">None</option>
    <option value="JS">JavaScript</option>
    <option value="aspnet">Asp.net</option>
    <option value="mvc">Asp.Net MVC</option>
</select>
<label id="result"></label>

$("#selector").change(function()
{
    $("#result").text($(this).val());
});

<asp:DropDownList AutoPostBack="true" runat="server" ID="myListDropDown"
                CssClass="text" OnSelectedIndexChanged="myListDropDown_Change" />

private void myListDropDown_SelectedIndexChanged(object sender, System.EventArgs e)
        {
                //put your code here
        }

private void dropdownlist_SelectedValueChanged(object sender, EventArgs e)
        {
                dropdownlist.Items["abc"]=label.text;
                dropdownlist.Items["xyz"]=label.text;

        }