我有一个由web方法生成的字符串/对象

[
  {
    "id": 367,
    "location": "Gagra"
  },
  {
    "id": 368,
    "location": "Gudauta"
  },
  {
    "id": 369,
    "location": "Sukhumi"
  },
  {
    "id": 370,
    "location": "Gulripshi"
  },
  {
    "id": 371,
    "location": "Ochamchira"
  },
  {
    "id": 372,
    "location": "Tkvarcheli"
  },
  {
    "id": 373,
    "location": "Gali"
  }
]

Web方法为

<WebMethod()>
Public Function PopulateStates(ByVal idLocation As Integer) As String
    Dim Locations As List(Of LocationData) = New List(Of LocationData)
    Dim JSONString As String
    Dim adp As New StatesTableAdapter
    Dim ds As StatesDataTable = adp.GetStatesByCountry(idLocation)
    If ds.Rows.Count > 0 Then
        For Each row As StatesRow In ds
            Dim ld As LocationData = New LocationData With {
                .id = row.idState,
                .location = row.locName
            }
            Locations.Add(ld)
        Next
    End If
    JSONString = JsonConvert.SerializeObject(Locations, Formatting.Indented)
    Return JSONString
End Function

Public Class LocationData
    Public Property id As Integer
    Public Property location As String
End Class

我 AJAX 调用如下所示

$('#ddlCountry').change(function (e) {
    $.ajax({
        type: "POST",
        url: "/TestWebService.asmx/PopulateStates",
        contentType: "application/json; charset=utf-8",
        data: '{"idLocation":"' + $(this).val() + '"}',
        dataType: "json",
        success: function (result, status, xhr) {
            console.log(result.d);
            $.each(result.d, function (key, value) {
                $("#ddlState").append($("<option></option>").val(value.id).html(value.location));
            });
        },
        error: function (xhr, status, error) {
            alert("Result: " + status + " " + error + " " + xhr.status + " " + xhr.statusText)
        }
    });
});

}）;
当字符串试图绑定到State下拉列表时，我收到一个错误，显示为Uncatch TypeError：无法使用'in'运算符在[中搜索'length'
问题出在Web方法中，还是没有正确处理结果？