[WebMethod]
    public static JsonResult GetMaintZone(string ddlState)
    {
        DataTable dt = new DataTable();
        try
        {
            CommonDB ObjCommon = new CommonDB();
            dt = ObjCommon.GetMZONE(ddlState);
        }
        catch (Exception)
        {

            throw;
        }
        return JsonResult(dt);

    }

function getMZONEWithState(evt) {

        var ddlState = $('#ContentPlaceHolder1_ddlState').val();

        var ddlMaintenanceZone = $("#ddlMaintenanceZone");

        ddlMaintenanceZone.empty().append('<option selected="selected" value="0" disabled = "disabled">State Loading...</option>');

        $.ajax({
            type: "POST",
            url: "Dashboard.aspx/GetMaintZone",
            data: JSON.stringify({ ddlState: ddlState }),
            contentType: "application/json; charset=utf-8",
            dataType: "json",
            success: function (response) {
                //fill ddl
            },
            error: function (response) {
                alert('Something went wrong..!!');
            }
        });
    }