blocks|key|4770768|text|您可以对对象的属性进行计数，并查看与上次检查时是否发生了更改：|type|unstyled|depth|inlineStyleRanges|entityRanges|data|4770769|How+to+efficiently+count+the+number+of+keys/properties+of+an+object+in+JavaScript?|offset|length|4770770|这是一个粗略的解决方法，用于在语言中找不到适当的功能支持的情况下使用。|4770771|entityMap|0|LINK|mutability|MUTABLE|url|https://stackoverflow.com/questions/126100/how-to-efficiently-count-the-number-of-keys-properties-of-an-object-in-javascrip^0|0|0|2A|0|0|0^^$0|@$1|2|3|4|5|6|7|P|8|@]|9|@]|A|$]]|$1|B|3|C|5|6|7|Q|8|@]|9|@$D|R|E|S|1|T]]|A|$]]|$1|F|3|G|5|6|7|U|8|@]|9|@]|A|$]]|$1|H|3|-4|5|6|7|V|8|@]|9|@]|A|$]]]|I|$J|$5|K|L|M|A|$N|O]]]]

You could count the properties on the object and see if has changed from when you last checked: 

<a href="https://stackoverflow.com/questions/126100/how-to-efficiently-count-the-number-of-keys-properties-of-an-object-in-javascrip">How to efficiently count the number of keys/properties of an object in JavaScript?</a>

this is a crude workaround, to use in case you can't find a proper support for the feature in the language.

blocks|key|4857050|text|从技术上讲，这是可能的，但因为我所知道的所有当前JS实现都是单线程的，所以它不会很优雅。我唯一能想到的就是暴力间隔：|type|unstyled|depth|inlineStyleRanges|entityRanges|data|4857051|var+checkObj+=+(function(watchObj)
{
++++var+initialMap+=+{},allProps+=+[],prop;
++++for+(prop+in+watchObj)
++++{
++++++++if+(watchObj.hasOwnProperty(prop))
++++++++{//make+tracer+object:+basically+clone+it
++++++++++++initialMap[prop]+=+watchObj[prop];
++++++++++++allProps.push(prop);//keep+an+array+mapper
++++++++}
++++}
++++return+function()
++++{
++++++++var+currentProps+=+[];
++++++++for+(prop+in+watchObj)
++++++++{
++++++++++++if+(watchObj.hasOwnProperty(prop))
++++++++++++{//iterate+the+object+again,+compare
++++++++++++++++if+(watchObj[prop]+!==+initialMap[prop])
++++++++++++++++{//type+andvalue+check!
++++++++++++++++++++console.log(initialMap[prop]+%2B+'+=>+'+watchObj[prop]);
++++++++++++++++++++//diff+found,+deal+with+it+whichever+way+you+see+fit
++++++++++++++++}
++++++++++++++++currentProps.push(prop);
++++++++++++}
++++++++}
++++++++//we're+not+done+yet!
++++++++if+(currentProps.length+<+allProps.length)
++++++++{
++++++++++++console.log('some+prop+was+deleted');
++++++++++++//loop+through+arrays+to+find+out+which+one
++++++++}
++++};
})(someObjectToTrack);
var+watchInterval+=+setInterval(checkObj,100);//check+every+.1+seconds?|code-block|syntax|javascript|4857052|这允许你在某种程度上跟踪一个物体，但同样，要做到10/秒是相当多的工作。谁知道呢，也许物体在两个间隔之间也会发生几次变化。|4857053|总而言之，我觉得这是一个不太理想的方法……也许比较JSON.stringify对象的字符串常量会更容易，但这确实意味着遗漏了函数和原型属性(尽管我在本例中将它们过滤掉了)。|offset|length|style|CODE|4857054|我曾经考虑过做一些类似的事情，但最终只是使用我的事件处理程序更改了有问题的对象来检查是否有任何更改。|4857055|或者，您也可以尝试创建一个DOMElement，并将onchange侦听器附加到该侦听器...不幸的是，同样，函数/方法可能很难跟踪，但至少它不会像上面的代码那样减慢脚本的速度。|4857056|entityMap^0|0|0|0|P|E|0|0|Q|8|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]]|$1|G|3|H|5|6|7|W|8|@]|9|@]|A|$]]|$1|I|3|J|5|6|7|X|8|@$K|Y|L|Z|M|N]]|9|@]|A|$]]|$1|O|3|P|5|6|7|10|8|@]|9|@]|A|$]]|$1|Q|3|R|5|6|7|11|8|@$K|12|L|13|M|N]]|9|@]|A|$]]|$1|S|3|-4|5|6|7|14|8|@]|9|@]|A|$]]]|T|$]]

this is possible, technically, but since all current JS implementations that I know of are single threaded it won't be very elegant. The only thing I can think of is a brute force interval:

<pre><code>var checkObj = (function(watchObj)
{
 var initialMap = {},allProps = [],prop;
 for (prop in watchObj)
 {
 if (watchObj.hasOwnProperty(prop))
 {//make tracer object: basically clone it
 initialMap[prop] = watchObj[prop];
 allProps.push(prop);//keep an array mapper
 }
 }
 return function()
 {
 var currentProps = [];
 for (prop in watchObj)
 {
 if (watchObj.hasOwnProperty(prop))
 {//iterate the object again, compare
 if (watchObj[prop] !== initialMap[prop])
 {//type andvalue check!
 console.log(initialMap[prop] + ' =&gt; ' watchObj[prop]);
 //diff found, deal with it whichever way you see fit
 }
 currentProps.push(prop);
 }
 }
 //we're not done yet!
 if (currentProps.length &lt; allProps.length)
 {
 console.log('some prop was deleted');
 //loop through arrays to find out which one
 }
 };
})(someObjectToTrack);
var watchInterval = setInterval(checkObj,100);//check every .1 seconds?
</code></pre>

That allows you to track an object to some extent, but again, it's quite a lot of work to do this 10/sec. Who knows, maybe the object changes several times in between the intervals, too. All in all, I feel as though this is a less-then-ideal approach... perhaps it would be easier to compare the string constants of the <code>JSON.stringify</code>'ed object, but that does mean missing out on functions, and (though I filtered them out in this example) prototype properties. 

I have considered doing something similar at one point, but ended up just using my event handlers that changed the object in question to check for any changes. 
Alternatively, you could also try creating a DOMElement, and attach an <code>onchange</code> listener to that... sadly, again, functions/methods might prove tricky to track, but at least it won't slow your script down as much as the code above will.

blocks|key|3127676|text|如果性能很重要，并且您可以控制更改对象的代码，请创建一个控件类来为您修改对象，例如|type|unstyled|depth|inlineStyleRanges|entityRanges|data|3127677|var+myObj+=+new+ObjectController({});

myObj.set('field',+{});
myObj.set('field.arr',+[{hello:+true}]);
myObj.set('field.arr.0.hello',+false);

var+obj+=+myObj.get('field');+//+obj+===+{field:+{arr:+[{hello:+false}]}}|code-block|syntax|javascript|3127678|在set()方法中，与设置时间间隔和定期扫描以检查更改相比，您现在能够以相当高的性能查看每个更改发生的位置。|3127679|我在ForerunnerDB中做了类似但高度优化的事情。在数据库上执行CRUD操作时，会为特定的字段路径激发更改事件，从而允许数据绑定视图在其基础数据发生更改时进行更新。|3127680|entityMap^0|0|0|0|0^^$0|@$1|2|3|4|5|6|7|M|8|@]|9|@]|A|$]]|$1|B|3|C|5|D|7|N|8|@]|9|@]|A|$E|F]]|$1|G|3|H|5|6|7|O|8|@]|9|@]|A|$]]|$1|I|3|J|5|6|7|P|8|@]|9|@]|A|$]]|$1|K|3|-4|5|6|7|Q|8|@]|9|@]|A|$]]]|L|$]]

If performance matters and you are in control of the code that changes the objects, create a control class that modifies your objects for you, e.g.

<pre><code>var myObj = new ObjectController({});

myObj.set('field', {});
myObj.set('field.arr', [{hello: true}]);
myObj.set('field.arr.0.hello', false);

var obj = myObj.get('field'); // obj === {field: {arr: [{hello: false}]}}
</code></pre>

In your set() method, you now have the ability to see where every change occurs in a pretty high-performance fashion, compared with setting an interval and doing regular scans to check for changes.

I do something similar but highly optimised in ForerunnerDB. When you do CRUD operations on the database, change events are fired for specific field paths, allowing data-bound views to be updated when their underlying data changes.

<pre><code>var obj = {};
obj.a = 1; // fire event, property "a" added 
</code></pre>

This question is different from <a href="https://stackoverflow.com/questions/1759987/listening-for-variable-changes-in-javascript-or-jquery">this one</a>, where ways to detect when an already declared property is changed, being discussed.

How to detect when a property is added to a JavaScript object?

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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var obj = {};obj.a = 1; // fire event, property "a" added 这个问题不同于，其中正在讨论检测已经声明的属性何时发生更改的方法。

问如何检测何时将属性添加到JavaScript对象？
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问如何检测何时将属性添加到JavaScript对象？EN