获取json中对象的长度

Question

我正在构建一个 Web 应用程序，用于显示某个站点的下一班车。

它使用 TransportAPI，从那里我得到一个 JSON 文件：https://transportapi.com/v3/uk/bus/stop/450023470/live.json?app_id=221cce2f&app_key=d209929236fc97196775650c2bdb639e&group=route&limit=2&nextbuses=yes

JSON 在一个数组中，我无法访问 29 内的数据

{
  "atcocode": "450023470",
  "smscode": "45023470",
  "request_time": "2017-05-11T11:57:51Z",
  "name": "Headingley Campus",
  "stop_name": "Headingley Campus",
  "bearing": "N",
  "indicator": "",
  "locality": "Beckett Park, Leeds",
  "departures": {
    "29": [
      {
        "mode": "bus",
        "line": "29",
        "line_name": "29",
        "direction": "Student Village",
        "operator": "FL",
        "date": "2017-05-11",
        "expected_departure_date": "2017-05-11",
        "aimed_departure_time": "13:05",
        "expected_departure_time": "13:05",
        "best_departure_estimate": "13:05",
        "source": "NextBuses",
        "dir": "inbound",
        "id": "https:\/\/transportapi.com\/v3\/uk\/bus\/route\/FL\/29\/inbound\/450023470\/2017-05-11\/13:05\/timetable.json?app_id=221cce2f&app_key=d209929236fc97196775650c2bdb639e",
        "operator_name": "First Leeds"
      }

以下内容有效，但我并不总是知道 [29] 的值是什么。

alert(obj['departures'][29].length);

如何在不知道值的情况下获得长度？

完整代码如下

$.ajax({
    type:"GET",
    dataType: 'JSONP',
    jsonpCallback: 'callback',
    url: "https://transportapi.com/v3/uk/bus/stop/450023470/live.json?app_id=221cce2f&app_key=d209929236fc97196775650c2bdb639e&group=route&limit=2&nextbuses=yes", 
    success: function(data) {
        var obj = jQuery.parseJSON(JSON.stringify(data));

alert(obj['departures'][29].length);

            //$("body").append(JSON.stringify(data['departures'][29][0]['line_name']));
            //alert(obj.departures.length);
        }, 
    error: function(jqXHR, textStatus, errorThrown) {
            alert(jqXHR.status);
        },

});

Answer 1

Object.keys(obj.departures) 将返回 obj.departures 的密钥。根据您的上下文，我假设只有一个键，在您的示例中是“29”。

所以只需将“29”替换为Object.keys(obj.departures)：

obj.departures[Object.keys(obj.departures)].length

请注意，您发布的代码显示的是常规对象，而不是 JSON。 JSON 是对象的字符串表示形式。

片段：

var obj = {
  //...
  "departures": {
    "randomkey": [
      {
        "mode": "bus",
  //...        
      },
      {
        "mode": "automobile",
  //...        
      },
      {
        "mode": "train"
  //...        
      }
    ]
  }
}
console.log(obj.departures[Object.keys(obj.departures)].length);  //3

Answer 2

只需迭代对象的属性：

var obj = JSON.parse(data); // Using native browser JSON parsing instead

if (obj.hasOwnProperty('departures')) { // Should validate just to be sure
    for (var i in obj['departures']) {
        console.log(i, obj['departures'][i], obj['departures'][i].length); // Or anything
    }
}

Answer 3

如果您对实际的键名不感兴趣，而只想将返回的总线线路作为数组获取，您可以将 departures-object 转换为数组

var depArr=Object.values(dataObj.departures);

var n=depArr.length 将为您提供所提供的不同公交线路的数量，depArr[i].length 将为您提供每条公交线路的次数 (i = 0...(n-1))。

Answer 4

尝试 Object.keys() ， Array.map() 与 ES6 箭头分配。

var jsonObj = {
"atcocode": "450023470",
"smscode": "45023470",
"request_time": "2017-05-13T18:42:12+01:00",
"bearing": "N",
"indicator": "",
"name": "Headingley Campus",
"locality": "Beckett Park, Leeds",
"stop_name": "Headingley Campus",
"departures": {
 "29": [
      {
        "mode": "bus",
        "line": "29",
        "line_name": "29",
        "direction": "Student Village",
        "operator": "FL",
        "date": "2017-05-11",
        "expected_departure_date": "2017-05-11",
        "aimed_departure_time": "13:05",
        "expected_departure_time": "13:05",
        "best_departure_estimate": "13:05",
        "source": "NextBuses",
        "dir": "inbound",
        "id": "https:\/\/transportapi.com\/v3\/uk\/bus\/route\/FL\/29\/inbound\/450023470\/2017-05-11\/13:05\/timetable.json?app_id=221cce2f&app_key=d209929236fc97196775650c2bdb639e",
        "operator_name": "First Leeds"
      }]
}
};

var res = Object.keys(jsonObj.departures).map(item => {return jsonObj.departures[item].length});

console.log(res);