JavaScript - 检查JSON中是否有特定的密钥

I am retrieving JSON from a live streaming data. For the first call I am getting dataset array with time and value. But in the second JSON dataset array is empty. I want to check if dataset array contains time key.

我正在从实时流数据中检索JSON。对于第一次调用，我将获得具有时间和值的数据集数组。但是在第二个JSON数据集数组中是空的。我想检查数据集数组是否包含时间密钥。

Retrieved JSON after first call:

首次调用后检索到JSON：

 {
  "activities-heart-intraday": {
    "dataset": [{
        "time": "00:00:00",
        "value": 91
    }, {
        "time": "00:01:00",
        "value": 92
    }, {
        "time": "00:02:00",
        "value": 92
    }],
    "datasetInterval": 1,
    "datasetType": "second"
  }
}

Retrieved JSON after second call:

第二次调用后检索JSON：

{
  "activities-heart-intraday": {
    "dataset": [],
    "datasetInterval": 1,
    "datasetType": "second"
  }
}

I am doing

我在做

var value = JSON.parse(data);

if (value.hasOwnProperty('time')) {
   console.log("here");
}

to check if time key exists in the JSON, but it's not working.

检查JSON中是否存在时间密钥，但它不起作用。

How can I check if a particular key exists in the array in json?

如何检查json中数组中是否存在特定键？

3 个解决方案

#1

Firstly you have to check that dataset is not an empty array. Then check that time is defined.

首先，您必须检查数据集是否为空数组。然后检查时间是否已定义。

This can be solved with:

这可以通过以下方式解决：

if (dataset[0] !== undefined && dataset[0].time !== undefined)

or just:

要不就：

if (dataset[0] && dataset[0].time)

If you want to iterate through the array:

如果要遍历数组：

dataset.forEach(function (data) {
   if (data.time) {
       // your code
   } 
});

#2

the data has a dataset array so we need to first check if the array is there and then if one of the arrays members has the time property

数据有一个数据集数组，所以我们需要首先检查数组是否存在，然后如果其中一个数组成员有时间属性

if( data.hasOwnProperty('dataset') && data.dataset.length != 0){    
  if( data.dataset[0].hasOwnProperty('time')){
    console.log('true');    
  }
}

#3

Since in JS you can not natively set and access object properties those with a "-" character in it by dot notation you have define them as strings and use bracket notation instead to set and access them. So you can make a check like this

因为在JS中你不能原生地设置和访问那些带有“ - ”字符的对象属性，用点符号将它们定义为字符串并使用括号表示法来设置和访问它们。所以你可以这样检查一下

data["activities-heart-intraday"].dataset.length > 0 && data["activities-heart-intraday"].dataset.every(e => !!e.time);

#1