blocks|key|1714133|text|您的data变量没有fields属性，这就是data.fields[2]无法工作的原因。我认为你要做的是data[fields[2]]，它适用于一个简单的对象，但你不能索引到一个像那样的复杂对象。|type|unstyled|depth|inlineStyleRanges|offset|length|style|CODE|entityRanges|data|1714134|entityMap^0|2|4|A|6|M|E|1G|F|0^^$0|@$1|2|3|4|5|6|7|H|8|@$9|I|A|J|B|C]|$9|K|A|L|B|C]|$9|M|A|N|B|C]|$9|O|A|P|B|C]]|D|@]|E|$]]|$1|F|3|-4|5|6|7|Q|8|@]|D|@]|E|$]]]|G|$]]

Your <code>data</code> variable doesn't have a <code>fields</code> property, and that's why <code>data.fields[2]</code> doesn't work. I think what you're trying to do there is <code>data[fields[2]]</code>, which would work for a simple object, but you can't index into a complex object like that.

blocks|key|4960469|text|老实说，我不能理解你的问题。JSON已经被结构化了，为什么还需要改变结构呢？|type|unstyled|depth|inlineStyleRanges|entityRanges|data|4960470|在您的情况下，我将访问它，如下所示：|4960471|data.address.streetName;|code-block|syntax|javascript|4960472|如果碰巧你想要遍历数据，你需要：|4960473|function+traverse_it(obj){
++++for(var+prop+in+obj){
++++++++if(typeof+obj[prop]=='object'){
++++++++++++//+object
++++++++++++traverse_it(obj[prop[i]]);
++++++++}else{
++++++++++++//+something+else
++++++++++++alert('The+value+of+'%2Bprop%2B'+is+'%2Bobj[prop]%2B'.');
++++++++}
++++}
}

traverse_it(data);|4960474|4960475|更新|offset|length|style|BOLD|4960476|在阅读下面的内容后，这个用户的需求似乎更明显了。给定字符串形式的属性名称，他/她想要访问对象。|4960477|function+findProp(obj,+prop,+defval){
++++if+(typeof+defval+==+'undefined')+defval+=+null;
++++prop+=+prop.split('.');
++++for+(var+i+=+0;+i+<+prop.length;+i%2B%2B)+{
++++++++if(typeof+obj[prop[i]]+==+'undefined')
++++++++++++return+defval;
++++++++obj+=+obj[prop[i]];
++++}
++++return+obj;
}

var+data+=+{"id":1,"name":"abc","address":{"streetName":"cde","streetId":2}};
var+props+=+'address.streetName';
alert('The+value+of+'+%2B+props+%2B+'+is+'+%2B+findProp(data,+props));|4960478|entityMap^0|0|0|0|0|0|0|0|2|0|0|0^^$0|@$1|2|3|4|5|6|7|Z|8|@]|9|@]|A|$]]|$1|B|3|C|5|6|7|10|8|@]|9|@]|A|$]]|$1|D|3|E|5|F|7|11|8|@]|9|@]|A|$G|H]]|$1|I|3|J|5|6|7|12|8|@]|9|@]|A|$]]|$1|K|3|L|5|F|7|13|8|@]|9|@]|A|$G|H]]|$1|M|3|-4|5|6|7|14|8|@]|9|@]|A|$]]|$1|N|3|O|5|6|7|15|8|@$P|16|Q|17|R|S]]|9|@]|A|$]]|$1|T|3|U|5|6|7|18|8|@]|9|@]|A|$]]|$1|V|3|W|5|F|7|19|8|@]|9|@]|A|$G|H]]|$1|X|3|-4|5|6|7|1A|8|@]|9|@]|A|$]]]|Y|$]]

To be honest, I can't understand your problem. JSON is already structured out, why do you need to change the structure?

In you case, I would access it as follows:

<pre><code>data.address.streetName;
</code></pre>

If, by any chance, what you want is to traverse the data, you would need:

<pre><code>function traverse_it(obj){
 for(var prop in obj){
 if(typeof obj[prop]=='object'){
 // object
 traverse_it(obj[prop[i]]);
 }else{
 // something else
 alert('The value of '+prop+' is '+obj[prop]+'.');
 }
 }
}

traverse_it(data);
</code></pre>

<hr>

Update

After reading below, what this user needs seems more obvious. Given property names as a string, s/he wants to access the object.

<pre><code>function findProp(obj, prop, defval){
 if (typeof defval == 'undefined') defval = null;
 prop = prop.split('.');
 for (var i = 0; i &lt; prop.length; i++) {
 if(typeof obj[prop[i]] == 'undefined')
 return defval;
 obj = obj[prop[i]];
 }
 return obj;
}

var data = {"id":1,"name":"abc","address":{"streetName":"cde","streetId":2}};
var props = 'address.streetName';
alert('The value of ' + props + ' is ' + findProp(data, props));
</code></pre>

blocks|key|923108|text|您可以这样访问它：data.address.streetName|type|unstyled|depth|inlineStyleRanges|offset|length|style|CODE|entityRanges|data|923109|entityMap^0|9|N|0^^$0|@$1|2|3|4|5|6|7|H|8|@$9|I|A|J|B|C]]|D|@]|E|$]]|$1|F|3|-4|5|6|7|K|8|@]|D|@]|E|$]]]|G|$]]

you can access it this way <code>data.address.streetName</code>

blocks|key|693612|text|JavaScript:|type|unstyled|depth|inlineStyleRanges|offset|length|style|BOLD|entityRanges|data|693613|function+getProperty(json,+path)+{
++++var+tokens+=+path.split(".");
++++var+obj+=+json;
++++for+(var+i+=+0;+i+<+tokens.length;+i%2B%2B)+{
++++++++obj+=+obj[tokens[i]];
++++}
++++return+obj;
}

var+data+=+{
++++id:+1,
++++name:+"abc",
++++address:+{
++++++++streetName:+"cde",
++++++++streetId:+2
++++}
};

var+fields+=+["id",+"name",+"address.streetName"];

for+(var+i+=+0;+i+<+fields.length;+i%2B%2B)+{
++++var+value+=+getProperty(data,+fields[i]);
++++console.log(fields[i]+%2B+"="+%2B+value);
}|code-block|syntax|javascript|693614|输出：|693615|id=1
name=abc
address.streetName=cde|693616|entityMap^0|0|B|0|0|0|3|0|0^^$0|@$1|2|3|4|5|6|7|Q|8|@$9|R|A|S|B|C]]|D|@]|E|$]]|$1|F|3|G|5|H|7|T|8|@]|D|@]|E|$I|J]]|$1|K|3|L|5|6|7|U|8|@$9|V|A|W|B|C]]|D|@]|E|$]]|$1|M|3|N|5|H|7|X|8|@]|D|@]|E|$I|J]]|$1|O|3|-4|5|6|7|Y|8|@]|D|@]|E|$]]]|P|$]]

JavaScript:

<pre><code>function getProperty(json, path) {
 var tokens = path.split(".");
 var obj = json;
 for (var i = 0; i &lt; tokens.length; i++) {
 obj = obj[tokens[i]];
 }
 return obj;
}

var data = {
 id: 1,
 name: "abc",
 address: {
 streetName: "cde",
 streetId: 2
 }
};

var fields = ["id", "name", "address.streetName"];

for (var i = 0; i &lt; fields.length; i++) {
 var value = getProperty(data, fields[i]);
 console.log(fields[i] + "=" + value);
}
</code></pre>

Output:

<pre><code>id=1
name=abc
address.streetName=cde
</code></pre>

blocks|key|4960572|text|长话短说，您可以使用数组表示法object[property]而不是object.property；这在键包含特殊字符时特别有用：|type|unstyled|depth|inlineStyleRanges|offset|length|style|CODE|entityRanges|data|4960573|var+data+=+{
++++"id":+1,
++++"name":+"abc",
++++"address":+{
++++++++"streetName":+"cde",
++++++++"streetId":+2
++++}
}

data.address.streetName;++++++++++++++//+(1)+dot+notation
data["address"]["streetName"];++++++++//+(2)+array+notation
var+field+=+"streetName";
data["address"][field];+++++++++++++++//+(3)+variable+inside+array+notation
var+fields+=+"address.streetName".split(".");
data[fields[0]][fields[1]];+++++++++++//+(4)+specific+to+your+question|code-block|syntax|javascript|4960574|在使用属性之前，可以使用typeof运算符检查该属性是否存在：|4960575|typeof+data["address"]["streetName"];+//+returns+"string"
typeof+data["address"]["foobarblah"];+//+returns+"undefined"|4960576|entityMap^0|F|G|Y|F|0|0|C|6|0|0^^$0|@$1|2|3|4|5|6|7|Q|8|@$9|R|A|S|B|C]|$9|T|A|U|B|C]]|D|@]|E|$]]|$1|F|3|G|5|H|7|V|8|@]|D|@]|E|$I|J]]|$1|K|3|L|5|6|7|W|8|@$9|X|A|Y|B|C]]|D|@]|E|$]]|$1|M|3|N|5|H|7|Z|8|@]|D|@]|E|$I|J]]|$1|O|3|-4|5|6|7|10|8|@]|D|@]|E|$]]]|P|$]]

Long story short, you can use the array notation <code>object[property]</code> instead of <code>object.property</code>; this is specially useful when the keys contains special characters:

<pre><code>var data = {
 "id": 1,
 "name": "abc",
 "address": {
 "streetName": "cde",
 "streetId": 2
 }
}

data.address.streetName; // (1) dot notation
data["address"]["streetName"]; // (2) array notation
var field = "streetName";
data["address"][field]; // (3) variable inside array notation
var fields = "address.streetName".split(".");
data[fields[0]][fields[1]]; // (4) specific to your question
</code></pre>

You can use the <code>typeof</code> operator to check whether a property exists or not before using it:

<pre><code>typeof data["address"]["streetName"]; // returns "string"
typeof data["address"]["foobarblah"]; // returns "undefined"
</code></pre>

blocks|key|923271|text|如果您使用lodash(一个非常流行的实用程序库)，则可以使用_.get()。|type|unstyled|depth|inlineStyleRanges|offset|length|style|CODE|entityRanges|data|923272|例如：|923273|var+data+=+{
++"id":1,
++"name":+"abc",
++"address":+{
++++"streetName":+"cde",
++++"streetId":2
++}
}
_.get(data,+'address.streetName');
//+'cde'
_.get(data,+['address',+'streetName']);
//+'cde'|code-block|syntax|javascript|923274|如果它涉及一个数组，你也可以使用像'address[0].streetName'这样的字符串路径。|923275|923276|var+data+=+{
++"id":1,
++"name":+"abc",
++"addresses":+[
++++{
++++++"streetName":+"cde",
++++++"streetId":+2
++++},
++++{
++++++"streetName":+"xyz",
++++++"streetId":+102
++++},
++]
}
_.get(data,+'addresses[0].streetName');
//+cde
_.get(data,+[address,+1,+streetName]);
//+xyz|923277|在内部，它使用toPath()函数将字符串路径(例如address.streetName)转换为数组(例如['address',+'streetName'])，然后使用一个函数访问对象中给定路径的数据。|923278|其他类似的实用函数包括_.set()和_.has()。看看他们。|923279|entityMap|0|LINK|mutability|MUTABLE|url|https://lodash.com/|1|https://lodash.com/docs#get^0|V|7|5|6|0|V|7|1|0|0|0|H|N|0|0|0|7|8|Q|I|1H|P|0|B|7|J|7|0^^$0|@$1|2|3|4|5|6|7|15|8|@$9|16|A|17|B|C]]|D|@$9|18|A|19|1|1A]|$9|1B|A|1C|1|1D]]|E|$]]|$1|F|3|G|5|6|7|1E|8|@]|D|@]|E|$]]|$1|H|3|I|5|J|7|1F|8|@]|D|@]|E|$K|L]]|$1|M|3|N|5|6|7|1G|8|@$9|1H|A|1I|B|C]]|D|@]|E|$]]|$1|O|3|G|5|6|7|1J|8|@]|D|@]|E|$]]|$1|P|3|Q|5|J|7|1K|8|@]|D|@]|E|$K|L]]|$1|R|3|S|5|6|7|1L|8|@$9|1M|A|1N|B|C]|$9|1O|A|1P|B|C]|$9|1Q|A|1R|B|C]]|D|@]|E|$]]|$1|T|3|U|5|6|7|1S|8|@$9|1T|A|1U|B|C]|$9|1V|A|1W|B|C]]|D|@]|E|$]]|$1|V|3|-4|5|6|7|1X|8|@]|D|@]|E|$]]]|W|$X|$5|Y|Z|10|E|$11|12]]|13|$5|Y|Z|10|E|$11|14]]]]

If you use <a href="https://lodash.com">lodash</a>(a very popular utility library), you can use <a href="https://lodash.com/docs#get"><code>_.get()</code></a>.

e.g.

<pre><code>var data = {
 "id":1,
 "name": "abc",
 "address": {
 "streetName": "cde",
 "streetId":2
 }
}
_.get(data, 'address.streetName');
// 'cde'
_.get(data, ['address', 'streetName']);
// 'cde'
</code></pre>

If it involves an array, you can use string path like <code>'address[0].streetName'</code> as well.

e.g.

<pre><code>var data = {
 "id":1,
 "name": "abc",
 "addresses": [
 {
 "streetName": "cde",
 "streetId": 2
 },
 {
 "streetName": "xyz",
 "streetId": 102
 },
 ]
}
_.get(data, 'addresses[0].streetName');
// cde
_.get(data, [address, 1, streetName]);
// xyz
</code></pre>

Internally, it uses <code>toPath()</code> function to convert string path (e.g. <code>address.streetName</code>) into an array (e.g. <code>['address', 'streetName']</code>), and then uses a function to access the data at the given path within the object.

Other similar utility functions include <code>_.set()</code> and <code>_.has()</code>. Check them out.

blocks|key|923307|text|这是我用来在嵌套对象中查找数据的函数：|type|unstyled|depth|inlineStyleRanges|entityRanges|data|923308|Object.prototype.find+=+function()+{
++try+{
++++return+Array.prototype.slice.call(arguments).reduce(function(acc,+key)+{
++++++return+acc[key]
++++},+this)
++}
++catch(e)+{
++++return+
++}
}|code-block|syntax|javascript|923309|数据结构：|923310|data+=+{
++"id":1,
++"name":"abc",
++"address":+{
++++"streetName":"cde",
++++"streetId":2
++}
}|923311|函数调用：|923312|data.find("address","streetName")|923313|返回：|923314|"cde"|923315|entityMap^0|0|0|0|0|0|0|0|0^^$0|@$1|2|3|4|5|6|7|U|8|@]|9|@]|A|$]]|$1|B|3|C|5|D|7|V|8|@]|9|@]|A|$E|F]]|$1|G|3|H|5|6|7|W|8|@]|9|@]|A|$]]|$1|I|3|J|5|D|7|X|8|@]|9|@]|A|$E|F]]|$1|K|3|L|5|6|7|Y|8|@]|9|@]|A|$]]|$1|M|3|N|5|D|7|Z|8|@]|9|@]|A|$E|F]]|$1|O|3|P|5|6|7|10|8|@]|9|@]|A|$]]|$1|Q|3|R|5|D|7|11|8|@]|9|@]|A|$E|F]]|$1|S|3|-4|5|6|7|12|8|@]|9|@]|A|$]]]|T|$]]

This is a function I use to find data in nested objects:

<pre><code>Object.prototype.find = function() {
 try {
 return Array.prototype.slice.call(arguments).reduce(function(acc, key) {
 return acc[key]
 }, this)
 }
 catch(e) {
 return 
 }
}
</code></pre>

Data structure:

<pre><code>data = {
 "id":1,
 "name":"abc",
 "address": {
 "streetName":"cde",
 "streetId":2
 }
}
</code></pre>

Function call:

<pre><code>data.find("address","streetName")
</code></pre>

Returns:

<pre><code>"cde"
</code></pre>

blocks|key|923317|text|我是这样做的：|type|unstyled|depth|inlineStyleRanges|entityRanges|data|923318|var+data+=+{
++++"id":+1,
++++"name":+"abc",
++++"addresses":+[{
++++++++"streetName":+"cde",
++++++++"streetId":+2
++++},+{
++++++++"streetName":+"xyz",
++++++++"streetId":+102
++++},+]
}

data2+=+data["addresses"]
for+(let+i+in+data2)+{
++++console.log(data2[i]["streetName"]);
}|code-block|syntax|javascript|923319|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|$]]

I did it like this:

<pre><code>var data = {
 "id": 1,
 "name": "abc",
 "addresses": [{
 "streetName": "cde",
 "streetId": 2
 }, {
 "streetName": "xyz",
 "streetId": 102
 }, ]
}

data2 = data["addresses"]
for (let i in data2) {
 console.log(data2[i]["streetName"]);
}
</code></pre>

Let say I have json data like 

<pre><code>data = {"id":1,
 "name":"abc",
 "address": {"streetName":"cde",
 "streetId":2
 }
 }
</code></pre>

Now I am getting fields to be accessed from this json data like : <code>fields = ["id", "name", "address.streetName"]</code>

How could I access third field (<code>address.streetName</code>) from given json data in most efficient way?
<code>data.fields[2]</code> doesn't work

One possibility is I construct <code>data[address][streetName]</code> string using a for loop and do eval of that but is there any efficient way of doing this?

How to access nested JSON data

翻译质量差，导致语言生硬或混乱。

没有提供实际的解决方法或示例。

解答不清晰，无法理解或解决问题。

页面排版不美观，阅读体验差。

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假设我有如下的json数据：data = {"id":1,        "name":"abc",        "address": {"streetName":"cde",                    "streetId":2                    }        }现在，我从这个js...

问如何访问嵌套的JSON数据
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问如何访问嵌套的JSON数据EN