jQuery Ajax jSon获取子数组数据

Question

我试图从curl PHP获取jSon数据。

以下是从网站获取的jSon数据。

我试图从子json数据中获取etd，note和value。

我收到错误但我无法在控制台中点击错误。它让我感到空白。

$('#kurir').change(function()
{
    var asal = $('#asal').val();
    var kab = $('#kabupaten').val();
    var kurir = $('#kurir').val();
    var berat = $('#berat').val();

    $.ajax({
        type : 'POST',
        url : 'cek_ongkir.php',
        dataType: "JSON",
        data :  {'kab_id' : kab, 'kurir' : kurir, 'asal' : asal, 'berat' : berat},
        success: function (jsonStr) {
            $.each(jsonStr.rajaongkir.results,function(index,item){
                var len = item.costs.length;

                for(var i=0; i<len; i++)
                {
                    alert(item[i].cost.value);
                }
            });
        }
    });
});

怎么做？

更新。
为了使它更详细，下面我将从网页添加json数据而不是屏幕截图。

请查看以下数据。

{rajaongkir: {query: {origin: "48", destination: "61", weight: 3080, 

courier: "jne"},…}}
rajaongkir
:
{query: {origin: "48", destination: "61", weight: 3080, courier: "jne"},…}
destination_details
:
{city_id: "61", province_id: "12", province: "Kalimantan Barat", type: "Kabupaten",…}
origin_details
:
{city_id: "48", province_id: "17", province: "Kepulauan Riau", type: "Kota", city_name: "Batam",…}
query
:
{origin: "48", destination: "61", weight: 3080, courier: "jne"}
results
:
[{code: "jne", name: "Jalur Nugraha Ekakurir (JNE)", costs: [,…]}]
0
:
{code: "jne", name: "Jalur Nugraha Ekakurir (JNE)", costs: [,…]}
code
:
"jne"
costs
:
[,…]
0
:
{service: "OKE", description: "Ongkos Kirim Ekonomis", cost: [{value: 141000, etd: "5-7", note: ""}]}
cost
:
[{value: 141000, etd: "5-7", note: ""}]
0
:
{value: 141000, etd: "5-7", note: ""}
description
:
"Ongkos Kirim Ekonomis"
service
:
"OKE"
1
:
{service: "REG", description: "Layanan Reguler", cost: [{value: 165000, etd: "3-5", note: ""}]}
cost
:
[{value: 165000, etd: "3-5", note: ""}]
0
:
{value: 165000, etd: "3-5", note: ""}
description
:
"Layanan Reguler"
service
:
"REG"
name
:
"Jalur Nugraha Ekakurir (JNE)"
status
:
{code: 200, description: "OK"}