blocks|key|3164699|text|您的问题是您的phones对象没有length属性(除非您在返回的JSON中的某个地方定义了它)，因为对象与数组不同，即使用作关联数组也是如此。如果phones对象是一个数组，那么它应该有一个长度。你有两个选择(也许更多)。|type|unstyled|depth|inlineStyleRanges|entityRanges|data|3164700|3164701|更改您的JSON结构(假设这是可能的)，这样'phones‘就变成了|ordered-list-item|3164702|3164703|“电话”：{"number":"XXXXXXXXXX","type":"mobile"},{"number":"XXXXXXXXXX","type":"mobile"}。在此响应中，phones.length将是有效的。|offset|length|style|CODE|3164704|遍历您的phones对象中包含的对象，并在执行过程中对它们进行计数，例如|unordered-list-item|3164705|3164706|var+key，count+=+0；for(data.phones+in+key){+if(data.phones.hasOwnProperty(key))+{+count%2B%2B；}+}|3164707|如果您只针对新的浏览器，那么选项2可能类似于this|3164708|entityMap|0|LINK|mutability|MUTABLE|url|note+there+is+no+word-numbered+identifier+for+each+phone+as+they+are+returned+in+a+0-indexed+array|1|https://stackoverflow.com/questions/126100/how-to-efficiently-count-the-number-of-keys-properties-of-an-object-in-javascript/4889658#4889658^0|0|0|0|0|2J|D|5|27|0|0|0|0|0|M|4|1|0^^$0|@$1|2|3|4|5|6|7|14|8|@]|9|@]|A|$]]|$1|B|3|-4|5|6|7|15|8|@]|9|@]|A|$]]|$1|C|3|D|5|E|7|16|8|@]|9|@]|A|$]]|$1|F|3|-4|5|6|7|17|8|@]|9|@]|A|$]]|$1|G|3|H|5|6|7|18|8|@$I|19|J|1A|K|L]]|9|@$I|1B|J|1C|1|1D]]|A|$]]|$1|M|3|N|5|O|7|1E|8|@]|9|@]|A|$]]|$1|P|3|-4|5|6|7|1F|8|@]|9|@]|A|$]]|$1|Q|3|R|5|6|7|1G|8|@]|9|@]|A|$]]|$1|S|3|T|5|6|7|1H|8|@]|9|@$I|1I|J|1J|1|1K]]|A|$]]|$1|U|3|-4|5|6|7|1L|8|@]|9|@]|A|$]]]|V|$W|$5|X|Y|Z|A|$10|11]]|12|$5|X|Y|Z|A|$10|13]]]]

Your problem is that your phones object doesn't have a length property (unless you define it somewhere in the JSON that you return) as objects aren't the same as arrays, even when used as associative arrays. If the phones object was an array it would have a length. You have two options (maybe more).

<ol>
<li>Change your JSON structure (assuming this is possible) so that 'phones' becomes 

<pre><code>"phones":[{"number":"XXXXXXXXXX","type":"mobile"},{"number":"XXXXXXXXXX","type":"mobile"}]
</code></pre>

(note there is no word-numbered identifier for each phone as they are returned in a 0-indexed array). In this response <code>phones.length</code> will be valid.</li>
<li>Iterate through the objects contained within your phones object and count them as you go, e.g.

<pre><code>var key, count = 0;
for(key in data.phones) {
 if(data.phones.hasOwnProperty(key)) {
 count++;
 }
}
</code></pre></li>
</ol>

If you're only targeting new browsers option 2 could look like <a href="https://stackoverflow.com/questions/126100/how-to-efficiently-count-the-number-of-keys-properties-of-an-object-in-javascript/4889658#4889658">this</a>

blocks|key|3164712|text|你可以使用像这样的|type|unstyled|depth|inlineStyleRanges|entityRanges|data|3164713|​|3164714|var+myObject+=+{'name':'Kasun',+'address':'columbo','age':+'29'}

var+count+=+Object.keys(myObject).length;
console.log(count);|code-block|syntax|javascript|3164715|3164716|entityMap^0|0|0|0|0^^$0|@$1|2|3|4|5|6|7|L|8|@]|9|@]|A|$]]|$1|B|3|C|5|6|7|M|8|@]|9|@]|A|$]]|$1|D|3|E|5|F|7|N|8|@]|9|@]|A|$G|H]]|$1|I|3|C|5|6|7|O|8|@]|9|@]|A|$]]|$1|J|3|-4|5|6|7|P|8|@]|9|@]|A|$]]]|K|$]]

You can use something like this
<div class="snippet" data-lang="js" data-hide="false" data-console="true" data-babel="false">
<div class="snippet-code">
<pre class="snippet-code-js lang-js prettyprint-override"><code>var myObject = {'name':'Kasun', 'address':'columbo','age': '29'}

var count = Object.keys(myObject).length;
console.log(count);</code></pre>
</div>
</div>

blocks|key|260821|text|考虑使用underscore.js。它将允许您检查大小，即像这样：|type|unstyled|depth|inlineStyleRanges|entityRanges|offset|length|data|260822|var+data+=+{one+:+1,+two+:+2,+three+:+3};
_.size(data);
//=>+3
_.keys(data);
//=>+["one",+"two",+"three"]
_.keys(data).length;
//=>+3|code-block|syntax|javascript|260823|entityMap|0|LINK|mutability|MUTABLE|url|http://underscorejs.org/^0|4|D|0|0|0^^$0|@$1|2|3|4|5|6|7|Q|8|@]|9|@$A|R|B|S|1|T]]|C|$]]|$1|D|3|E|5|F|7|U|8|@]|9|@]|C|$G|H]]|$1|I|3|-4|5|6|7|V|8|@]|9|@]|C|$]]]|J|$K|$5|L|M|N|C|$O|P]]]]

Consider using <a href="http://underscorejs.org">underscore.js</a>. It will allow you to check the size i.e. like that:

<pre><code>var data = {one : 1, two : 2, three : 3};
_.size(data);
//=&gt; 3
_.keys(data);
//=&gt; ["one", "two", "three"]
_.keys(data).length;
//=&gt; 3
</code></pre>

blocks|key|2950943|text|$(document).ready(function+()+{
++++$('#count_my_data').click(function+()+{
++++++++var+count+=+0;
++++++++while+(true)+{
+++++++++++++try+{
++++++++++++++++var+v1+=+mydata[count].TechnologyId.toString();
++++++++++++++++count+=+count+%2B+1;
++++++++++++}
++++++++++++catch+(e)
++++++++++++{+break;+}
++++++++}
++++++++alert(count);
++++});
});|type|code-block|depth|inlineStyleRanges|entityRanges|data|syntax|javascript|2950944|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>$(document).ready(function () {
 $('#count_my_data').click(function () {
 var count = 0;
 while (true) {
 try {
 var v1 = mydata[count].TechnologyId.toString();
 count = count + 1;
 }
 catch (e)
 { break; }
 }
 alert(count);
 });
});
</code></pre>

blocks|key|260828|text|var+json=[{"id":"431","code":"0.85.PSFR01215","price":"2457.77","volume":"23.0","total":"565.29"},{"id":"430","code":"0.85.PSFR00608","price":"1752.45","volume":"4.0","total":"70.1"},{"id":"429","code":"0.84.SMAB00060","price":"4147.5","volume":"2.0","total":"82.95"},{"id":"428","code":"0.84.SMAB00050","price":"4077.5","volume":"3.0","total":"122.32"}]+
var+obj+=+JSON.parse(json);
var+length+=+Object.keys(obj).length;+//you+get+length+json+result+4|type|code-block|depth|inlineStyleRanges|entityRanges|data|syntax|javascript|260829|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>var json=[{"id":"431","code":"0.85.PSFR01215","price":"2457.77","volume":"23.0","total":"565.29"},{"id":"430","code":"0.85.PSFR00608","price":"1752.45","volume":"4.0","total":"70.1"},{"id":"429","code":"0.84.SMAB00060","price":"4147.5","volume":"2.0","total":"82.95"},{"id":"428","code":"0.84.SMAB00050","price":"4077.5","volume":"3.0","total":"122.32"}] 
var obj = JSON.parse(json);
var length = Object.keys(obj).length; //you get length json result 4
</code></pre>

blocks|key|2950962|text|你不需要改变你的JSON格式。|type|unstyled|depth|inlineStyleRanges|entityRanges|data|2950963|替换：|2950964|console.log(data.phones.length);|code-block|syntax|javascript|2950965|通过以下方式：|2950966|console.log(+Object.keys(+data.phones+).length+)+;|2950967|entityMap^0|0|0|0|0|0^^$0|@$1|2|3|4|5|6|7|O|8|@]|9|@]|A|$]]|$1|B|3|C|5|6|7|P|8|@]|9|@]|A|$]]|$1|D|3|E|5|F|7|Q|8|@]|9|@]|A|$G|H]]|$1|I|3|J|5|6|7|R|8|@]|9|@]|A|$]]|$1|K|3|L|5|F|7|S|8|@]|9|@]|A|$G|H]]|$1|M|3|-4|5|6|7|T|8|@]|9|@]|A|$]]]|N|$]]

you dont need to change your JSON format.

replace:

<pre><code>console.log(data.phones.length);
</code></pre>

with:

<pre><code>console.log( Object.keys( data.phones ).length ) ;
</code></pre>

blocks|key|258573|text|使用这个|type|unstyled|depth|inlineStyleRanges|entityRanges|data|258574|Object.keys(jsonObject).length|258575|entityMap^0|0|0^^$0|@$1|2|3|4|5|6|7|F|8|@]|9|@]|A|$]]|$1|B|3|C|5|6|7|G|8|@]|9|@]|A|$]]|$1|D|3|-4|5|6|7|H|8|@]|9|@]|A|$]]]|E|$]]

use this one
Object.keys(jsonObject).length

blocks|key|264052|text|尝尝这个|type|unstyled|depth|inlineStyleRanges|entityRanges|data|264053|$.parseJSON(data).length|code-block|syntax|javascript|264054|entityMap^0|0|0^^$0|@$1|2|3|4|5|6|7|I|8|@]|9|@]|A|$]]|$1|B|3|C|5|D|7|J|8|@]|9|@]|A|$E|F]]|$1|G|3|-4|5|6|7|K|8|@]|9|@]|A|$]]]|H|$]]

try this

<pre><code>$.parseJSON(data).length
</code></pre>

i have a JSON object that gets returned by an AJAX request and I am having some trouble with the <code>.length</code> because it keeps returning <code>undefined</code>. Just wondering if I'm using it right:
<pre><code>console.log(data.length);
console.log(data.phones.length);
</code></pre>
They both return <code>undefined</code> even though they are valid objects.
Update: 
Sample of the JSON object returned:
<pre><code>{&quot;reqStatus&quot;:true,&quot;phones&quot;:{&quot;one&quot;:{&quot;number&quot;:&quot;XXXXXXXXXX&quot;,&quot;type&quot;:&quot;mobile&quot;},&quot;two&quot;:{&quot;number&quot;:&quot;XXXXXXXXXX&quot;,&quot;type&quot;:&quot;mobile&quot;}}}
</code></pre>

get size of JSON object

JSON

我有一个由AJAX请求返回的JSON对象，但我在使用.length时遇到了一些问题，因为它总是返回undefined。只是想知道我是否用对了：console.log(data.length);console.log(data.phones.length);它们都返回undefined，即使它们是有效的对象。更新：返回的...

问获取JSON对象的大小
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