通过索引检索JSON对象的属性？ [英] Retrieving a property of a JSON object by index?

问题描述

假设这个JSON对象：

Assuming this JSON object:

var obj = {
    "set1": [1, 2, 3],
    "set2": [4, 5, 6, 7, 8],
    "set3": [9, 10, 11, 12]
};

可以像这样检索set2属性：

The "set2" property may be retrieved like so:

obj["set2"]

是有没有办法通过索引检索set2属性？它是JSON对象的第二个属性。这当然不起作用：

Is there a way to retrieve the "set2" property by index? It is the second property of the JSON object. This does not work (of course):

obj[1]  

所以，我想说我想要检索JSON对象的第二个属性，但我不知道它的名字 - 那我该怎么做呢？

So, let's say that I want to retrieve the second property of the JSON object, but I don't know its name - how would I do it then?

更新： 是的，我知道对象是无序属性的集合。但我不认为浏览器会混淆JSON文字/字符串定义的原始顺序。

Update: Yes, I understand that objects are collections of unordered properties. But I don't think that the browsers mess with the "original" order defined by the JSON literal / string.

推荐答案

对象在JavaScript中是无序属性的集合。对象是哈希表。

Objects in JavaScript are collections of unordered properties. Objects are hashtables.

如果您希望属性按字母顺序排列，一种可能的解决方案是在单独的数组中为属性创建索引。就在几个小时前，我回答了一个关于Stack Overflow的问题你可能想看看：

If you want your properties to be in alphabetical order, one possible solution would be to create an index for your properties in a separate array. Just a few hours ago, I answered a question on Stack Overflow which you may want to check out:

• 在排序中对JavaScript对象进行迭代基于子对象的特定键值的顺序

• Iterating over a JavaScript object in sort order based on particular key value of a child object

这是一个快速适应你的对象 ¹ ：

Here's a quick adaptation for your object¹:

var obj = {
    "set1": [1, 2, 3],
    "set2": [4, 5, 6, 7, 8],
    "set3": [9, 10, 11, 12]
};

var index = [];

// build the index
for (var x in obj) {
   index.push(x);
}

// sort the index
index.sort(function (a, b) {    
   return a == b ? 0 : (a > b ? 1 : -1); 
}); 

然后你可以做到以下几点：

Then you would be able to do the following:

console.log(obj[index[1]]);

我引用的答案早先提出了一个可重用的解决方案来迭代这样的对象。除非您可以将JSON更改为 @Jacob Relkin在另一个答案中建议，这可能会更容易。

The answer I cited earlier proposes a reusable solution to iterate over such an object. That is unless you can change your JSON to as @Jacob Relkin suggested in the other answer, which could be easier.

¹ 您可能想使用 hasOwnProperty（） 方法，以确保属性属于您的对象，并且不从 Object.prototype 继承。

¹ You may want to use the hasOwnProperty() method to ensure that the properties belong to your object and are not inherited from Object.prototype.

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