blocks|key|2684823|text|它只是用来精确描述对象应该如何行为的一种手段。|type|unstyled|depth|inlineStyleRanges|entityRanges|data|2684824|它们不是对象的真正成员，即使在某些实现中它们是，您也不能使用可移植代码访问它们。|2684825|换句话说，这是一种编写规范的方法，允许使用命令性代码描述行为，这种代码在形式上比仅仅使用冗长的“自然语言”描述行为应该是什么更加精确。|2684826|entityMap^0|0|0|0^^$0|@$1|2|3|4|5|6|7|H|8|@]|9|@]|A|$]]|$1|B|3|C|5|6|7|I|8|@]|9|@]|A|$]]|$1|D|3|E|5|6|7|J|8|@]|9|@]|A|$]]|$1|F|3|-4|5|6|7|K|8|@]|9|@]|A|$]]]|G|$]]

<p>It's simply an artifice used to be able to describe precisely how the objects should behave.</p>

<p>They are not real members of the objects and even if in some implementation they are you are not allowed to access them with portable code.</p>

<p>In other words it's a way to write the specification that allows describing behavior with imperative code that is formally more precise that just using a wordy "natural-language" description of what the behavior should be.</p>


blocks|key|127443|text|摘要|type|unstyled|depth|inlineStyleRanges|entityRanges|data|127444|内部插槽/方法是规范用来定义所需行为的伪属性/+-methods。(“抽象操作”是规范的相关机制。)槽代表状态(值)，方法描述算法(行为)。它们可能对应于引擎使用的对象的属性，也可能不对应于引擎使用的对象的属性，但用户代码不能使用它们，除非由公共API的某些部分公开。引擎使用的实际实现可能与内部方法勾勒出的非常不同，但为了符合要求，它们必须产生与内部方法一致的行为或结果。|127445|示例|127446|[[StringData]]内部插槽|offset|length|style|CODE|127447|String的行为，例如new+String("whatever")，以包括表示值的[[StringData]]内部槽(在本例中为whatever)的术语来描述。用户代码不能直接访问内部插槽，但String.prototype.toString()+(例如(new+String("whatever")).toString())是根据thisStringValue()抽象操作定义的，该抽象操作通过返回[[StringData]]的值来描述。所以换句话说，String.prototype.toString()是一个公开[[StringData]]的getter。|127448|[[OwnPropertyKeys]]内部方法|127449|使用包括调用[[OwnPropertyKeys]]内部方法在内的术语来描述Object.keys()的行为。注意，不同种类的对象，例如普通对象(例如Object)和奇异对象(例如String)可能具有不同的[[OwnPropertyKeys]]定义。当在规范中“调用”[[OwnPropertyKeys]]时，它指的是适用类型的定义。对于任何对象类型，还有一些适用于其定义的invariant特征。|127450|entityMap|0|LINK|mutability|MUTABLE|url|http://www.ecma-international.org/ecma-262/6.0/#sec-object.keys|1|http://www.ecma-international.org/ecma-262/6.0/#sec-ordinary-object-internal-methods-and-internal-slots-ownpropertykeys|2|http://www.ecma-international.org/ecma-262/6.0/#sec-string-exotic-objects-ownpropertykeys|3|http://www.ecma-international.org/ecma-262/6.0/#sec-invariants-of-the-essential-internal-methods^0|0|0|0|0|E|0|0|6|C|M|16|E|1T|8|2P|R|3K|Z|4N|H|5L|E|6C|R|78|E|0|0|J|0|6|J|11|D|22|6|2H|6|2V|J|3Q|J|11|D|0|22|6|1|2H|6|2|57|9|3|0^^$0|@$1|2|3|4|5|6|7|15|8|@]|9|@]|A|$]]|$1|B|3|C|5|6|7|16|8|@]|9|@]|A|$]]|$1|D|3|E|5|6|7|17|8|@]|9|@]|A|$]]|$1|F|3|G|5|6|7|18|8|@$H|19|I|1A|J|K]]|9|@]|A|$]]|$1|L|3|M|5|6|7|1B|8|@$H|1C|I|1D|J|K]|$H|1E|I|1F|J|K]|$H|1G|I|1H|J|K]|$H|1I|I|1J|J|K]|$H|1K|I|1L|J|K]|$H|1M|I|1N|J|K]|$H|1O|I|1P|J|K]|$H|1Q|I|1R|J|K]|$H|1S|I|1T|J|K]|$H|1U|I|1V|J|K]]|9|@]|A|$]]|$1|N|3|O|5|6|7|1W|8|@$H|1X|I|1Y|J|K]]|9|@]|A|$]]|$1|P|3|Q|5|6|7|1Z|8|@$H|20|I|21|J|K]|$H|22|I|23|J|K]|$H|24|I|25|J|K]|$H|26|I|27|J|K]|$H|28|I|29|J|K]|$H|2A|I|2B|J|K]]|9|@$H|2C|I|2D|1|2E]|$H|2F|I|2G|1|2H]|$H|2I|I|2J|1|2K]|$H|2L|I|2M|1|2N]]|A|$]]|$1|R|3|-4|5|6|7|2O|8|@]|9|@]|A|$]]]|S|$T|$5|U|V|W|A|$X|Y]]|Z|$5|U|V|W|A|$X|10]]|11|$5|U|V|W|A|$X|12]]|13|$5|U|V|W|A|$X|14]]]]

<h1>Summary</h1>

<p>Internal slots / methods are pseudo-properties / -methods that the specification uses to define required behavior. ("Abstract operations" are a related mechanism of the spec.) Slots represent state (values), and methods describe algorithms (behavior). They may or may not correspond to properties of objects used by the engine, but they're not available to user code, except as exposed by some part of the public API. The actual implementation an engine uses may be very different from what the internal methods sketch out, but to be compliant they have to produce behavior or results that are consistent with the internal methods.</p>

<h1>Examples</h1>

<h2><code>[[StringData]]</code> internal slot</h2>

<p>The behavior of <code>String</code>, e.g. <code>new String("whatever")</code>, is described in terms that include a <code>[[StringData]]</code> internal slot that represents the value (<code>whatever</code> in this case). The internal slot isn't directly accessible to user code, but <code>String.prototype.toString()</code> (e.g. <code>(new String("whatever")).toString()</code>) is defined in terms of a <code>thisStringValue()</code> abstract operation, which is described in terms of returning the value of <code>[[StringData]]</code>. So in other words, <code>String.prototype.toString()</code> is public API that is essentially a getter that exposes <code>[[StringData]]</code>.</p>

<h2><code>[[OwnPropertyKeys]]</code> internal method</h2>

<p>The behavior of <a href="http://www.ecma-international.org/ecma-262/6.0/#sec-object.keys" rel="noreferrer"><code>Object.keys()</code></a> is described in terms that include calling the <code>[[OwnPropertyKeys]]</code> internal method. Note that different kinds of objects, such as ordinary objects (e.g. <a href="http://www.ecma-international.org/ecma-262/6.0/#sec-ordinary-object-internal-methods-and-internal-slots-ownpropertykeys" rel="noreferrer"><code>Object</code></a>) and exotic objects (e.g. <a href="http://www.ecma-international.org/ecma-262/6.0/#sec-string-exotic-objects-ownpropertykeys" rel="noreferrer"><code>String</code></a>) may have different definitions of <code>[[OwnPropertyKeys]]</code>. When <code>[[OwnPropertyKeys]]</code> is "called" in the spec, that refers to the definition for the applicable type. There are also some <a href="http://www.ecma-international.org/ecma-262/6.0/#sec-invariants-of-the-essential-internal-methods" rel="noreferrer">invariant</a> characteristics that apply to its definition for any object type.</p>


<p>I've tried to understand ECMAScript 2015 specification in one point: <a href="http://www.ecma-international.org/ecma-262/6.0/#sec-object-internal-methods-and-internal-slots">Internal Slots of Objects</a>. But this section appeared very unclear to me, especially this sentence:</p>

<blockquote>
  <p>Internal slots correspond to internal state that is associated with objects and used by various ECMAScript specification algorithms.</p>
</blockquote>

<p>(Does it use correct grammar?) Can anybody explain this notion in English?</p>

<hr>

<p>What I can understand so far:</p>

<ul>
<li>internal slots are not properties</li>
<li>internal slots are used during the creation of an object, but not added to the object itself</li>
<li>internal slots are or have <em>values</em>, initially <code>undefined</code></li>
</ul>


What is an "internal slot" of an object in JavaScript?

我试着在一点上理解ECMAScript 2015规范：。但这一节对我来说似乎非常不清楚，特别是这句话：内部插槽对应于与对象关联并由各种ECMAScript规范算法使用的内部状态。(它使用了正确的语法吗？)有人能用英语解释这个概念吗？到目前为止我能理解的是：在创建对象期间使用propertiesinternal插槽，但不...

问什么是JavaScript中对象的“内部槽”？
EN

社区

活动

资源

关于

腾讯云开发者

热门产品

热门推荐

更多推荐

问什么是JavaScript中对象的“内部槽”？EN

社区

活动

资源

关于

腾讯云开发者

热门产品

热门推荐

更多推荐

问什么是JavaScript中对象的“内部槽”？
EN