blocks|key|426315|text|in还将检查继承的属性，而hasOwnProperty并非如此。|type|unstyled|depth|inlineStyleRanges|offset|length|style|CODE|entityRanges|data|426316|entityMap^0|0|2|D|E|0^^$0|@$1|2|3|4|5|6|7|H|8|@$9|I|A|J|B|C]|$9|K|A|L|B|C]]|D|@]|E|$]]|$1|F|3|-4|5|6|7|M|8|@]|D|@]|E|$]]]|G|$]]

<code>in</code> will also check for inherited properties, which is not the case for <code>hasOwnProperty</code>.

blocks|key|208171|text|第一个版本更短(尤其是在变量被重命名的精简代码中)|type|unstyled|depth|inlineStyleRanges|entityRanges|data|208172|a+in+b|code-block|syntax|javascript|208173|vs|208174|b.hasOwnProperty(a)|208175|无论如何，正如@AndreMeinhold所说，它们并不总是产生相同的结果。|208176|entityMap^0|0|0|0|0|0^^$0|@$1|2|3|4|5|6|7|O|8|@]|9|@]|A|$]]|$1|B|3|C|5|D|7|P|8|@]|9|@]|A|$E|F]]|$1|G|3|H|5|6|7|Q|8|@]|9|@]|A|$]]|$1|I|3|J|5|D|7|R|8|@]|9|@]|A|$E|F]]|$1|K|3|L|5|6|7|S|8|@]|9|@]|A|$]]|$1|M|3|-4|5|6|7|T|8|@]|9|@]|A|$]]]|N|$]]

The first version is shorter (especially in minified code where the variables are renamed)

<pre><code>a in b
</code></pre>

vs 

<pre><code>b.hasOwnProperty(a)
</code></pre>

Anyway, as @AndreMeinhold said, they do not always produce the same result.

blocks|key|208217|text|你得到了一些很棒的答案。我只是想提供一些东西，让你在迭代对象时省去检查"hasOwnProperty“的需要。|type|unstyled|depth|inlineStyleRanges|entityRanges|data|208218|当创建一个对象时，人们通常会这样创建它：|208219|const+someMap+=+{}
//+equivalent+to:+Object.create(Object.prototype)
//+someMap.constructor+will+yield+->+function+Object()+{+[native+code]+}|code-block|syntax|javascript|208220|现在，如果你想遍历"someMap“，你必须这样做：|208221|const+key
for(key+in+someMap+){
+if+(someMap.hasOwnProperty(key))+{+
+++//+Do+something
+}
}|208222|我们这样做是为了避免对继承的属性进行迭代。|208223|如果您打算创建一个仅用作“映射”(即键-值对)的简单对象，您可以这样做：|208224|const+newMap+=+Object.create(null);
//+Now,+newMap+won't+have+prototype+at+all.
//+newMap.constructor+will+yield+->+undefined|208225|所以现在可以安全地像这样迭代了：|208226|for(key+in+cleanMap){
+console.log(key+%2B+"+->+"+%2B+newMap+[key]);
+//+No+need+to+add+extra+checks,+as+the+object+will+always+be+clean
}|208227|我学到了这个很棒的技巧here|offset|length|208228|entityMap|0|LINK|mutability|MUTABLE|url|http://www.jstips.co/en/javascript/hash-maps-without-side-effects/^0|0|0|0|0|0|0|0|0|0|0|B|4|0|0^^$0|@$1|2|3|4|5|6|7|18|8|@]|9|@]|A|$]]|$1|B|3|C|5|6|7|19|8|@]|9|@]|A|$]]|$1|D|3|E|5|F|7|1A|8|@]|9|@]|A|$G|H]]|$1|I|3|J|5|6|7|1B|8|@]|9|@]|A|$]]|$1|K|3|L|5|F|7|1C|8|@]|9|@]|A|$G|H]]|$1|M|3|N|5|6|7|1D|8|@]|9|@]|A|$]]|$1|O|3|P|5|6|7|1E|8|@]|9|@]|A|$]]|$1|Q|3|R|5|F|7|1F|8|@]|9|@]|A|$G|H]]|$1|S|3|T|5|6|7|1G|8|@]|9|@]|A|$]]|$1|U|3|V|5|F|7|1H|8|@]|9|@]|A|$G|H]]|$1|W|3|X|5|6|7|1I|8|@]|9|@$Y|1J|Z|1K|1|1L]]|A|$]]|$1|10|3|-4|5|6|7|1M|8|@]|9|@]|A|$]]]|11|$12|$5|13|14|15|A|$16|17]]]]

You got some really great answers.
I just want to offer something that will save you the need for checking "hasOwnProperty" while iterating an object.

When creating an object usually people will create it in this way:

<pre><code>const someMap = {}
// equivalent to: Object.create(Object.prototype)
// someMap.constructor will yield -&gt; function Object() { [native code] }
</code></pre>

Now, if you want to iterate through "someMap" you will have to do it this way:

<pre><code>const key
for(key in someMap ){
 if (someMap.hasOwnProperty(key)) { 
 // Do something
 }
}
</code></pre>

We are doing so in order to avoid iterating over inherited properties.

If you intend to create a simple object that will only be used as a "map" (i.e. key - value pairs) you can do so like that:

<pre><code>const newMap = Object.create(null);
// Now, newMap won't have prototype at all.
// newMap.constructor will yield -&gt; undefined
</code></pre>

So now it will be safe to iterate like this:

<pre><code>for(key in cleanMap){
 console.log(key + " -&gt; " + newMap [key]);
 // No need to add extra checks, as the object will always be clean
}
</code></pre>

I learned this awesome tip <a href="http://www.jstips.co/en/javascript/hash-maps-without-side-effects/" rel="noreferrer">here</a>

Do the following two statements produce the same output? Is there any reason to prefer one way to the other?

<pre><code> if (key in object)

 if (object.hasOwnProperty(key))
</code></pre>

if (key in object) or if(object.hasOwnProperty(key)

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。

文章

问答

视频

学习中心

腾讯云实验室

直播

竞赛

腾讯云代码分析专区

腾讯iOA零信任安全管理系统专区

腾讯云架构师技术同盟交流圈

腾讯云数据库专区

腾讯云顾问专区

腾讯云原生专区

腾讯混元专区

腾讯云TCE专区

腾讯云Lighthouse专区

腾讯云HAI专区

腾讯云Edgeone专区

腾讯云存储专区

腾讯云智能专区

腾讯轻联专区 

腾讯云开发专区

TAPD专区

腾讯轻量云游戏服专区

腾讯云最具价值专家

腾讯云架构师技术同盟

腾讯云创作之星

腾讯云开发者先锋 

腾讯云代码助手

CODING DevOps

Cloud Studio

SDK中心

API中心

命令行工具

以下两条语句是否产生相同的输出？有理由选择其中一种而不是另一种吗？ if (key in object) if (object.hasOwnProperty(key))

问if (对象中的键)或if(object.hasOwnProperty(键)
EN

社区

活动

圈层

关于

腾讯云开发者

热门产品

热门推荐

更多推荐

问if (对象中的键)或if(object.hasOwnProperty(键)EN

社区

活动

圈层

关于

腾讯云开发者

热门产品

热门推荐

更多推荐

问if (对象中的键)或if(object.hasOwnProperty(键)
EN