如何访问嵌套数组？答案

【问题标题】：How to access nested arrays?如何访问嵌套数组？
【发布时间】：2018-12-19 07:55:57
【问题描述】：

我正在尝试从天气应用返回的 JSON 访问 JavaScript 中的嵌套数组。但是，如果控制台不返回cannot return property of 'x' of undefined，我似乎无法访问任何数据。我相当确定问题在于我如何与result 进行交互，但我不确定。有谁知道我如何正确访问嵌套数组中的数据？

这是我目前不工作的代码：

const weather = require('weather-js');

var val;
var temp;
var final;

weather.find({search: 'Oceanside, CA', degreeType: 'F'}, function(err, result){         
  if (err) console.log(err);

  obj = JSON.stringify(result, null, 2);
  temp = result[2].current.temperature;
  console.log(temp);
  final = result[1].location.name;
  console.log(final)
});

这是我尝试与之交互的 JSON：

[
  {
    "location": {
      "name": "Oceanside, CA",
      "lat": "33.197",
      "long": "-117.381",
      "timezone": "-8",
      "alert": "",
      "degreetype": "F",
      "imagerelativeurl": "http://blob.weather.microsoft.com/static/weather4/en-us/"
    },
    "current": {
      "temperature": "55",
      "skycode": "31",
      "skytext": "Mostly Clear",
      "date": "2018-12-18",
      "observationtime": "22:15:00",
      "observationpoint": "Oceanside, CA",
      "feelslike": "55",
      "humidity": "90",
      "winddisplay": "3 mph Southwest",
      "day": "Tuesday",
      "shortday": "Tue",
      "windspeed": "3 mph",
      "imageUrl": "http://blob.weather.microsoft.com/static/weather4/en-us/law/31.gif"
    },
    "forecast": [
      {
        "low": "46",
        "high": "64",
        "skycodeday": "29",
        "skytextday": "Partly Cloudy",
        "date": "2018-12-17",
        "day": "Monday",
        "shortday": "Mon",
        "precip": ""
      },
      {
        "low": "45",
        "high": "65",
        "skycodeday": "34",
        "skytextday": "Mostly Sunny",
        "date": "2018-12-18",
        "day": "Tuesday",
        "shortday": "Tue",
        "precip": "0"
      },
      {
        "low": "44",
        "high": "67",
        "skycodeday": "34",
        "skytextday": "Mostly Sunny",
        "date": "2018-12-19",
        "day": "Wednesday",
        "shortday": "Wed",
        "precip": "0"
      },
      {
        "low": "47",
        "high": "69",
        "skycodeday": "30",
        "skytextday": "Partly Sunny",
        "date": "2018-12-20",
        "day": "Thursday",
        "shortday": "Thu",
        "precip": "0"
      },
      {
        "low": "47",
        "high": "65",
        "skycodeday": "34",
        "skytextday": "Mostly Sunny",
        "date": "2018-12-21",
        "day": "Friday",
        "shortday": "Fri",
        "precip": "0"
      }
    ]
  }
]

这个问题不是 Access / process（嵌套）对象、数组或 JSON 的副本，因为据我所知，该页面上的答案涉及多个元素的数组，而这个问题没有。

【问题讨论】：

cannot return property of 'x' of undefined 您的问题中的代码中没有x，但该错误出现在哪一行？（这听起来像是释义错误，而不是实际错误 - 请发布实际错误）
它实际上并没有说“x”。如果我们要具体，它会显示当前或位置。 X 只是为了简单。
result 中有一个 single 元素数组。这就是您在result[2].* 上收到错误的原因
你的结果数组只有一个元素。这是一个对象，您正在尝试访问索引处不是零的元素。
这个问题与 JSON 本身无关。除了未使用的（！）obj，任何地方都没有 JSON。

标签： javascript arrays json multidimensional-array

【解决方案1】：

//try this its working
var j = [{
  "location": {
    "name": "Oceanside, CA",
    "lat": "33.197",
    "long": "-117.381",
    "timezone": "-8",
    "alert": "",
    "degreetype": "F",
    "imagerelativeurl": "http://blob.weather.microsoft.com/static/weather4/en-us/"
  },
  "current": {
    "temperature": "55",
    "skycode": "31",
    "skytext": "Mostly Clear",
    "date": "2018-12-18",
    "observationtime": "22:15:00",
    "observationpoint": "Oceanside, CA",
    "feelslike": "55",
    "humidity": "90",
    "winddisplay": "3 mph Southwest",
    "day": "Tuesday",
    "shortday": "Tue",
    "windspeed": "3 mph",
    "imageUrl": "http://blob.weather.microsoft.com/static/weather4/en-us/law/31.gif"
  },
  "forecast": [{
      "low": "46",
      "high": "64",
      "skycodeday": "29",
      "skytextday": "Partly Cloudy",
      "date": "2018-12-17",
      "day": "Monday",
      "shortday": "Mon",
      "precip": ""
    },
    {
      "low": "45",
      "high": "65",
      "skycodeday": "34",
      "skytextday": "Mostly Sunny",
      "date": "2018-12-18",
      "day": "Tuesday",
      "shortday": "Tue",
      "precip": "0"
    },
    {
      "low": "44",
      "high": "67",
      "skycodeday": "34",
      "skytextday": "Mostly Sunny",
      "date": "2018-12-19",
      "day": "Wednesday",
      "shortday": "Wed",
      "precip": "0"
    },
    {
      "low": "47",
      "high": "69",
      "skycodeday": "30",
      "skytextday": "Partly Sunny",
      "date": "2018-12-20",
      "day": "Thursday",
      "shortday": "Thu",
      "precip": "0"
    },
    {
      "low": "47",
      "high": "65",
      "skycodeday": "34",
      "skytextday": "Mostly Sunny",
      "date": "2018-12-21",
      "day": "Friday",
      "shortday": "Fri",
      "precip": "0"
    }
  ]
}];
console.log(j[0].current.temperature);
console.log(j[0].location.name);

【讨论】：

【解决方案2】：

这很简单。假设 JavaScript 中的数组定义为 var myArray=[]

您会注意到您的 JSON 有一个外部 []，并且在此您有 1 个外部 {}，这意味着它在数组中的索引 0 处有 1 个元素。

所以，不要做result[2].current.temperature;，而是做result[0].current.temperature；

使用 result[2] 会给你 undefined 因为它不存在！

【讨论】：