var json_obj =
{
"40": [{ "title": "all", "name": "all promotions", "id": "all" },{}],
"20": { "title": "best_room_rate", "name": "best room rate", "id": "best_room_rate" },
"10": { "title": "summer rate", "name": "summer rate", "id": "30" }
}

for (var item in json_obj) {
alert(item);//10->20->40
}
请问这里输出结果为什么不是40->20->10呢