Question

我有一个Json对象，基本上是一个数组，在每个数组中我想迭代属性，所以我做了这样的事情：

for(var x = 0;x<dados.feeds.length;x++){
        for(var y in dados.feeds[x]){
            console.log(dados.feeds[x][y]);
            /*if(data == dataInicial){
                console.log("a");
            }*/
        }
    }

console.log（dados.feeds[x][0]）给了我undefined，我只想要每个x行的第一个元素，我怎么能得到它？

json object dados

{
  "channel":
  {
    "id": 9,
    "name": "my_house",
    "description": "Netduino Plus connected to sensors around the house",
    "latitude": "40.44",
    "longitude": "-79.996",
    "field1": "Light",
    "field2": "Outside Temperature",
    "created_at": "2010-12-13T20:20:06-05:00",
    "updated_at": "2014-02-26T12:43:04-05:00",
    "last_entry_id": 6060625
  },
  "feeds":
  [
    {
      "created_at": "2014-02-26T12:42:49-05:00",
      "entry_id": 6060624,
      "field1": "188",
      "field2": "25.902335456475583"
    },
    {
      "created_at": "2014-02-26T12:43:04-05:00",
      "entry_id": 6060625,
      "field1": "164",
      "field2": "25.222929936305732"
    }
  ]
}

Answer 1

您的数据如何？如果它与

类似

var dados = {
  feeds: [ {a: 'aa'}, {b: 'bb'} ]
}

然后你可以试试这个：

dados.feeds.forEach(feed => {
  Object.keys(feed).forEach((key, index) => {
    if(index === 0) { console.log(feed[key]) } // aa bb...
  })
})

HTH

Answer 2

应为console.log(dados.feeds[x].created_at);。

Answer 3

虽然you shouldn't rely on Javascript object key order，但这是一个解决方案，它将返回feeds数组中每个条目中第一个键的值;

var dados = {
  "channel":
  {
    "id": 9,
    "name": "my_house",
    "description": "Netduino Plus connected to sensors around the house",
    "latitude": "40.44",
    "longitude": "-79.996",
    "field1": "Light",
    "field2": "Outside Temperature",
    "created_at": "2010-12-13T20:20:06-05:00",
    "updated_at": "2014-02-26T12:43:04-05:00",
    "last_entry_id": 6060625
  },
  "feeds":
  [
    {
      "created_at": "2014-02-26T12:42:49-05:00",
      "entry_id": 6060624,
      "field1": "188",
      "field2": "25.902335456475583"
    },
    {
      "created_at": "2014-02-26T12:43:04-05:00",
      "entry_id": 6060625,
      "field1": "164",
      "field2": "25.222929936305732"
    }
  ]
};

var con = document.getElementById('console');
for (var i = 0; i < dados.feeds.length; i++) {
    var firstKey = Object.keys(dados.feeds[i])[0];
    con.innerHTML += '<p>' + dados.feeds[i][firstKey] + '</p>';
}

/*
Prints;

2014-02-26T12:42:49-05:00

2014-02-26T12:43:04-05:00

*/

Here是工作代码的小提琴。

Answer 4

你拥有它的代码运行良好，一切都没有出现，没有任何未定义（我试过）。

但是，console.log [x] [0]将跟踪undefined，因为：

var x = 0;
var obj = feeds[x]; // this will be the first object from the feeds array.
console.log ( obj [ 0 ] );

你现在可能已经看到了;将跟踪undefined，因为该obj没有0属性。它是具有键/值的对象。

所以这会奏效：

var each = 'created_at';
console.log ( obj [ each ] );

而且：

for ( var each in obj ) {
   console.log ( each, obj [ each ] );
}

获取for..in二维中的第一个元素

4 个答案: