blocks|key|812280|text|我不认为Numbers等有默认的toJSON实现。也许您正在使用Prototype或其他框架？|type|unstyled|depth|inlineStyleRanges|entityRanges|data|812281|http://www.w3schools.com/jsref/jsref_obj_number.asp|offset|length|812282|http://www.w3schools.com/jsref/jsref_obj_array.asp|812283|来自http://www.prototypejs.org/learn/json：|812284|812285|编码|blockquote|812286|812287|Prototype的JSON编码与Crockford的实现略有不同，因为它没有扩展Object.prototype。以下方法可用:+Number#toJSON、String#toJSON、Array#toJSON、Hash#toJSON、Date#toJSON和Object.toJSON。|812288|entityMap|0|LINK|mutability|MUTABLE|url|1|2|http://www.prototypejs.org/learn/json^0|0|0|1F|0|0|0|1E|1|0|2|11|2|0|0|0|0|0^^$0|@$1|2|3|4|5|6|7|10|8|@]|9|@]|A|$]]|$1|B|3|C|5|6|7|11|8|@]|9|@$D|12|E|13|1|14]]|A|$]]|$1|F|3|G|5|6|7|15|8|@]|9|@$D|16|E|17|1|18]]|A|$]]|$1|H|3|I|5|6|7|19|8|@]|9|@$D|1A|E|1B|1|1C]]|A|$]]|$1|J|3|-4|5|6|7|1D|8|@]|9|@]|A|$]]|$1|K|3|L|5|M|7|1E|8|@]|9|@]|A|$]]|$1|N|3|-4|5|6|7|1F|8|@]|9|@]|A|$]]|$1|O|3|P|5|6|7|1G|8|@]|9|@]|A|$]]|$1|Q|3|-4|5|6|7|1H|8|@]|9|@]|A|$]]]|R|$S|$5|T|U|V|A|$W|C]]|X|$5|T|U|V|A|$W|G]]|Y|$5|T|U|V|A|$W|Z]]]]

I don't think its the case that Numbers, etc have default toJSON implementations. Maybe you are using Prototype or some other framework?

<a href="http://www.w3schools.com/jsref/jsref_obj_number.asp" rel="nofollow noreferrer">http://www.w3schools.com/jsref/jsref_obj_number.asp</a>

<a href="http://www.w3schools.com/jsref/jsref_obj_array.asp" rel="nofollow noreferrer">http://www.w3schools.com/jsref/jsref_obj_array.asp</a>

From <a href="http://www.prototypejs.org/learn/json" rel="nofollow noreferrer">http://www.prototypejs.org/learn/json</a> :

<blockquote>
 Encoding 
 
 Prototype’s JSON encoding slightly
 differs from Crockford’s
 implementation as it does not extend
 Object.prototype. The following
 methods are available: Number#toJSON,
 String#toJSON, Array#toJSON,
 Hash#toJSON, Date#toJSON and
 Object.toJSON.
</blockquote>

blocks|key|1972952|text|我怀疑这是一个原因-数组似乎也没有它们。下面是我将如何实现它：|type|unstyled|depth|inlineStyleRanges|entityRanges|data|1972953|Array.prototype.toJSON+=+Object.prototype.toJSON+=+function()+{
++return+JSON.stringify(this);
}|code-block|syntax|javascript|1972954|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 doubt this is a reason - arrays don't seem to have them either. Here's how I'd implement it:

<pre><code>Array.prototype.toJSON = Object.prototype.toJSON = function() {
 return JSON.stringify(this);
}
</code></pre>

blocks|key|2220719|text|这是不在任意对象上实现函数的标准。|type|unstyled|depth|inlineStyleRanges|entityRanges|data|2220720|尝试使用console.log({})，您将什么也看不到。|offset|length|style|CODE|2220721|entityMap^0|0|4|F|0^^$0|@$1|2|3|4|5|6|7|J|8|@]|9|@]|A|$]]|$1|B|3|C|5|6|7|K|8|@$D|L|E|M|F|G]]|9|@]|A|$]]|$1|H|3|-4|5|6|7|N|8|@]|9|@]|A|$]]]|I|$]]

It's a standard to not implement functions on arbitrary objects.

try <code>console.log({})</code> and you'll see nothing.

blocks|key|672021|text|你提到的那些方法是由一些JavaScript引擎添加的(AFAIK，最新版本的V8和Tracemonkey实现了它们)：|type|unstyled|depth|inlineStyleRanges|entityRanges|data|672022|String.prototype.toJSON
Boolean.prototype.toJSON
Number.prototype.toJSON
Date.prototype.toJSON|code-block|syntax|javascript|672023|尽管ECMAScript+5规范唯一标准化的是Date.prototype.toJSON。|offset|length|style|CODE|672024|就我个人而言，我认为这些方法用处不大，来自String、Boolean和Number的结果完全等同于调用valueOf方法，来自Date的结果等同于调用toISOString。|672025|所以问题是:为什么本机对象没有toJSON()方法？|672026|在JSON对象可用的情况下(15.12节)，向Object.prototype添加另一个方法是不值得的，而且我真的认为添加它是一个坏主意……|672027|entityMap|0|LINK|mutability|MUTABLE|url|http://www.ecma-international.org/publications/files/ECMA-ST/ECMA-262.pdf^0|0|0|N|L|2|C|0|0|L|6|S|7|10|6|1G|7|24|B|0|0|1|4|N|G|0^^$0|@$1|2|3|4|5|6|7|10|8|@]|9|@]|A|$]]|$1|B|3|C|5|D|7|11|8|@]|9|@]|A|$E|F]]|$1|G|3|H|5|6|7|12|8|@$I|13|J|14|K|L]]|9|@$I|15|J|16|1|17]]|A|$]]|$1|M|3|N|5|6|7|18|8|@$I|19|J|1A|K|L]|$I|1B|J|1C|K|L]|$I|1D|J|1E|K|L]|$I|1F|J|1G|K|L]|$I|1H|J|1I|K|L]]|9|@]|A|$]]|$1|O|3|P|5|6|7|1J|8|@]|9|@]|A|$]]|$1|Q|3|R|5|6|7|1K|8|@$I|1L|J|1M|K|L]|$I|1N|J|1O|K|L]]|9|@]|A|$]]|$1|S|3|-4|5|6|7|1P|8|@]|9|@]|A|$]]]|T|$U|$5|V|W|X|A|$Y|Z]]]]

Those methods you mention were added by some JavaScript engines (AFAIK the latest versions of V8 and Tracemonkey implement them):

<pre><code>String.prototype.toJSON
Boolean.prototype.toJSON
Number.prototype.toJSON
Date.prototype.toJSON
</code></pre>

Although the only standarized by the <a href="http://www.ecma-international.org/publications/files/ECMA-ST/ECMA-262.pdf" rel="noreferrer">ECMAScript 5</a> Specification is the <code>Date.prototype.toJSON</code>.

Personally I think those methods aren't much useful at all, the results from <code>String</code>, <code>Boolean</code>, and <code>Number</code> are completely equivalent to calling the <code>valueOf</code> method, and the result from Date is equivalent to calling <code>toISOString</code>.

So the question was: Why native objects not have a toJSON() method?

Well, with the <code>JSON</code> Object available (Section 15.12), adding another method to the <code>Object.prototype</code> is not worth, and really I think it would be a bad idea adding it...

blocks|key|672037|text|真正的原因|type|unstyled|depth|inlineStyleRanges|entityRanges|data|672038|虽然@CMS是正确的，但浏览器添加了这些，这一点完全被忽略了。原因是JSON规范为任何对象调用了一个可选的toJSON方法，然后调用该方法来将非标准化结构序列化为标准化结构。|offset|length|style|BOLD|CODE|672039|var+O+=+function+O()+{
++++this.val+=+'value';
++++this.toJSON+=+function+()+{+return+['VALUE!'];+};
};

var+o+=+new+O();
var+s+=+JSON.stringify(o);

console.log(s);++//+>>+["VALUE!"]|code-block|syntax|javascript|672040|一个例子是集合数据结构，它的结构实际上是一个具有values方法的对象。这将允许编写this.toJSON+=+values;来为JSON.stringify方法提供正确的序列化策略。|672041|因此，简而言之，它的目的是为JSON.stringify提供正确的输出替代结构的策略。|672042|希望这能有所帮助。|672043|entityMap^0|0|Y|6|1Y|7|1H|6|0|0|O|6|16|L|1T|E|0|E|E|0|0^^$0|@$1|2|3|4|5|6|7|V|8|@]|9|@]|A|$]]|$1|B|3|C|5|6|7|W|8|@$D|X|E|Y|F|G]|$D|Z|E|10|F|G]|$D|11|E|12|F|H]]|9|@]|A|$]]|$1|I|3|J|5|K|7|13|8|@]|9|@]|A|$L|M]]|$1|N|3|O|5|6|7|14|8|@$D|15|E|16|F|H]|$D|17|E|18|F|H]|$D|19|E|1A|F|H]]|9|@]|A|$]]|$1|P|3|Q|5|6|7|1B|8|@$D|1C|E|1D|F|H]]|9|@]|A|$]]|$1|R|3|S|5|6|7|1E|8|@]|9|@]|A|$]]|$1|T|3|-4|5|6|7|1F|8|@]|9|@]|A|$]]]|U|$]]

<h3>The Real Reason</h3>

While @CMS is correct, the Browser makes have added these, the point was missed entirely. The reason is that the JSON Specification calls for an optional <code>toJSON</code> method for any object which, in turn, gets called to serialize a non-normative structure into a normative one.

<pre><code>var O = function O() {
 this.val = 'value';
 this.toJSON = function () { return ['VALUE!']; };
};

var o = new O();
var s = JSON.stringify(o);

console.log(s); // &gt;&gt; ["VALUE!"]
</code></pre>

An example would be a Set Data-Structure whose structure is actually an object which has a <code>values</code> method. This would allow one to write <code>this.toJSON = values;</code> to provide the <code>JSON.stringify</code> method the right serialization-strategy.

So, in a nutshell, its to provide <code>JSON.stringify</code> the correct strategy for outputting alternative structures.

Hope this helps.

As described at <a href="http://www.json.org/js.html" rel="noreferrer">http://www.json.org/js.html</a>, JavaScript objects can dictate how they are serialized by JSON.stringify() by implementing a toJSON() method. For an arbitrary object, this method is not defined, while numbers and strings seem to implement the method. I'm curious--why do objects not have an implementation?

EDIT: I originally mentioned that arrays have this method--they do not. I apologize for the confusion.

Why do JavaScript objects not have a toJSON() method?

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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正如在中所描述的，JavaScript对象可以通过实现JSON.stringify()方法来指定toJSON()如何序列化它们。对于任意对象，此方法未定义，而数字和字符串似乎实现了此方法。我很好奇--为什么对象没有实现？EDIT:我最初提到数组有这个方法--它们没有。我为造成的混乱道歉。

问为什么JavaScript对象没有toJSON()方法？
EN

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问为什么JavaScript对象没有toJSON()方法？EN