blocks|key|337294|text|问得好。除了在for-in循环中迭代之外，我不知道还有什么方法。不过，您只需要迭代一次。为安全起见，请确保它是已知属性[more+info]。|type|unstyled|depth|inlineStyleRanges|entityRanges|offset|length|data|337295|for+(var+propName+in+jsonObj)+{
++++if+(jsonObj.hasOwnProperty(propName))+{
++++++++return+propName;++++//+or+do+something+with+it+and+break
++++}
}|code-block|syntax|javascript|337296|对进行了编辑，以便更清楚地表明您迭代的是属性名称，而不是它们的值。|style|BOLD|337297|entityMap|0|LINK|mutability|MUTABLE|url|http://javascript.crockford.com/code.html^0|1O|9|0|0|0|0|1|0^^$0|@$1|2|3|4|5|6|7|U|8|@]|9|@$A|V|B|W|1|X]]|C|$]]|$1|D|3|E|5|F|7|Y|8|@]|9|@]|C|$G|H]]|$1|I|3|J|5|6|7|Z|8|@$A|10|B|11|K|L]]|9|@]|C|$]]|$1|M|3|-4|5|6|7|12|8|@]|9|@]|C|$]]]|N|$O|$5|P|Q|R|C|$S|T]]]]

Great question. I don't know of any way besides iterating in a for-in loop. You only need to iterate once though. For safety, ensure it's a known property [<a href="http://javascript.crockford.com/code.html" rel="nofollow noreferrer">more info</a>].

<pre><code>for (var propName in jsonObj) {
 if (jsonObj.hasOwnProperty(propName)) {
 return propName; // or do something with it and break
 }
}
</code></pre>

Edited to be extra clear that you're iterating over the property names, not their values.

blocks|key|3315265|text|没有"first“属性。对象的属性是无序的。|type|unstyled|depth|inlineStyleRanges|entityRanges|data|3315266|您可以获得JS引擎决定首先使用循环提供的任何一个。|3315267|function+maybe_first_in_object(ob)+{
++++for+(var+props+in+ob)+{
++++++++return+prop;
++++}
}|code-block|syntax|javascript|3315268|…但如果顺序很重要，请使用数组而不是对象。|3315269|entityMap^0|0|0|0|0^^$0|@$1|2|3|4|5|6|7|M|8|@]|9|@]|A|$]]|$1|B|3|C|5|6|7|N|8|@]|9|@]|A|$]]|$1|D|3|E|5|F|7|O|8|@]|9|@]|A|$G|H]]|$1|I|3|J|5|6|7|P|8|@]|9|@]|A|$]]|$1|K|3|-4|5|6|7|Q|8|@]|9|@]|A|$]]]|L|$]]

There isn't a "first" property. The properties of an object are unordered.

You can get whatever one the JS engine decides to provide first with a loop.

<pre><code>function maybe_first_in_object(ob) {
 for (var props in ob) {
 return prop;
 }
}
</code></pre>

&hellip; but if the order matters, use an array not an object.

blocks|key|3315313|text|不能保证对象属性的顺序与您放入它们的方式相同。然而，在实践中，所有主流浏览器都会按顺序返回它们。所以如果你不介意的话...|type|unstyled|depth|inlineStyleRanges|entityRanges|data|3315314|var+firstProp;
for(var+key+in+jsonObj)+{
++++if(jsonObj.hasOwnProperty(key))+{
++++++++firstProp+=+jsonObj[key];
++++++++break;
++++}
}|code-block|syntax|javascript|3315315|还要注意的是，有一个关于排序的bug+in+Chrome，在某些边缘情况下，它不会按照提供的方式对它进行排序。至于它在未来的变化，机会实际上是相当小的，因为我相信这将成为标准的一部分，所以如果有什么支持的话，只会成为官方的。|offset|length|3315316|但是，如果你真的、真的、绝对、肯定地想要确保它的顺序是正确的，那么你需要使用一个数组。否则，上面的代码就可以了。|3315317|相关问题：Elements+order+-+for+(…+in+…)+loop+in+javascript|3315318|entityMap|0|LINK|mutability|MUTABLE|url|http://ejohn.org/blog/javascript-in-chrome/|1|https://stackoverflow.com/questions/280713/elements-order-for-in-loop-in-javascript^0|0|0|F|D|0|0|0|5|1C|1|0^^$0|@$1|2|3|4|5|6|7|Y|8|@]|9|@]|A|$]]|$1|B|3|C|5|D|7|Z|8|@]|9|@]|A|$E|F]]|$1|G|3|H|5|6|7|10|8|@]|9|@$I|11|J|12|1|13]]|A|$]]|$1|K|3|L|5|6|7|14|8|@]|9|@]|A|$]]|$1|M|3|N|5|6|7|15|8|@]|9|@$I|16|J|17|1|18]]|A|$]]|$1|O|3|-4|5|6|7|19|8|@]|9|@]|A|$]]]|P|$Q|$5|R|S|T|A|$U|V]]|W|$5|R|S|T|A|$U|X]]]]

The order of the properties of an object are not guaranteed to be the same as the way you put them in. In practice, however, all major browsers do return them in order. So if you're okay with relying on this...

<pre><code>var firstProp;
for(var key in jsonObj) {
 if(jsonObj.hasOwnProperty(key)) {
 firstProp = jsonObj[key];
 break;
 }
}
</code></pre>

Also note that there's a <a href="http://ejohn.org/blog/javascript-in-chrome/" rel="noreferrer">bug in Chrome</a> regarding the ordering, in some edge cases it doesn't order it in the way they were provided. As far as it changing in the future, the chances are actually pretty small as I believe this is becoming part of the standard so if anything support for this will only become official.

All things considered, though, if you really, really, absolutely, positively, want to be sure it's going to be in the right order you need to use an array. Otherwise, the above is fine.

Related question: <a href="https://stackoverflow.com/questions/280713/elements-order-for-in-loop-in-javascript">Elements order - for (… in …) loop in javascript</a>

blocks|key|3315326|text|在使用jQuery时，您还可以使用$.each遍历JSON对象。看起来比使用for-loop更整洁|type|unstyled|depth|inlineStyleRanges|offset|length|style|CODE|entityRanges|data|3315327|var+items+=+{
++++'item1':+'content',
++++'item2':+'content',
++++'item3':+'content'
}

$.each(items,+function()+{+
++++console.log($(this)[0])
})|code-block|syntax|javascript|3315328|entityMap^0|H|6|12|3|0|0^^$0|@$1|2|3|4|5|6|7|M|8|@$9|N|A|O|B|C]|$9|P|A|Q|B|C]]|D|@]|E|$]]|$1|F|3|G|5|H|7|R|8|@]|D|@]|E|$I|J]]|$1|K|3|-4|5|6|7|S|8|@]|D|@]|E|$]]]|L|$]]

When using jQuery, you can also use <code>$.each</code> to iterate over a JSON object. Looks cleaner IMO than using a <code>for</code>-loop

<pre><code>var items = {
 'item1': 'content',
 'item2': 'content',
 'item3': 'content'
}

$.each(items, function() { 
 console.log($(this)[0])
})
</code></pre>

blocks|key|3102437|text|console.log(jsonObj[Object.keys(jsonObj)[0]]);|type|code-block|depth|inlineStyleRanges|entityRanges|data|syntax|javascript|3102438|unstyled|entityMap^0|0^^$0|@$1|2|3|4|5|6|7|G|8|@]|9|@]|A|$B|C]]|$1|D|3|-4|5|E|7|H|8|@]|9|@]|A|$]]]|F|$]]

<pre><code>console.log(jsonObj[Object.keys(jsonObj)[0]]);
</code></pre>

Is there a way to get the name of the first property of a JSON object?
I'd like to do something like this:
<pre><code>var firstProp = jsonObj[0];
</code></pre>
edit: I'm getting a JSON object which hold categories of arrays with image
URLs.
like so:
<pre><code>{
 &quot;category1&quot;:[&quot;image/url/1.jpg&quot;,&quot;image/url/2.jpg&quot;],
 &quot;category2&quot;:[&quot;image/url/3.jpg&quot;,&quot;image/url/4.jpg&quot;]
}
</code></pre>
I am then iterating through the object to insert the images, and all I really wanted was an elegant way to see which category was inserted first. At first I just did
<pre><code>for (var cat in images) {
 if (i==0) firstCat = cat;
 ...
}
</code></pre>
But that some how &quot;felt&quot; ugly... So it was basically just a question of elegance.

Getting first JSON property

jQuery

JSON

有没有办法获得JSON对象的第一个属性的名称？我想做这样的事情：var firstProp = jsonObj[0];JSON edit：我正在获取一个JSON对象，它包含带有图像URL的数组类别。如下所示：{  "category1":["image/url/1.jpg","image/url/2.jpg"],  "...

问获取第一个JSON属性
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