blocks|key|639513|text|是的，ID是唯一的。类则不是。|type|unstyled|depth|inlineStyleRanges|entityRanges|data|639514|entityMap^0|0^^$0|@$1|2|3|4|5|6|7|D|8|@]|9|@]|A|$]]|$1|B|3|-4|5|6|7|E|8|@]|9|@]|A|$]]]|C|$]]

<p>Yes, IDs are unique. Class are not.</p>


blocks|key|639612|text|来自mdn|type|unstyled|depth|inlineStyleRanges|entityRanges|data|639613|📷|atomic|offset|length|639614|https://developer.mozilla.org/en/DOM/element.id|639615|所以我想最好是...|639616|entityMap|0|IMAGE|mutability|IMMUTABLE|imageUrl|https://ask.qcloudimg.com/http-save/yehe-900000/93a8770d29dbd86c9164946ff2719068.jpeg|imageAlt|1|LINK|MUTABLE|url^0|0|0|1|0|0|0|1B|1|0|0^^$0|@$1|2|3|4|5|6|7|X|8|@]|9|@]|A|$]]|$1|B|3|C|5|D|7|Y|8|@]|9|@$E|Z|F|10|1|11]]|A|$]]|$1|G|3|H|5|6|7|12|8|@]|9|@$E|13|F|14|1|15]]|A|$]]|$1|I|3|J|5|6|7|16|8|@]|9|@]|A|$]]|$1|K|3|-4|5|6|7|17|8|@]|9|@]|A|$]]]|L|$M|$5|N|O|P|A|$Q|R|S|-4]]|T|$5|U|O|V|A|$W|H]]]]

<p>from mdn <img src="https://i.stack.imgur.com/VrJwr.jpg" alt="enter image description here" />
<a href="https://developer.mozilla.org/en/DOM/element.id" rel="noreferrer">https://developer.mozilla.org/en/DOM/element.id</a></p>
<p>so i guess it better be...</p>


blocks|key|425276|text|这基本上就是ID的全部意义所在。:)+ID是特定的，每个页面只能使用一次。类可以随意使用。|type|unstyled|depth|inlineStyleRanges|entityRanges|data|425277|entityMap^0|0^^$0|@$1|2|3|4|5|6|7|D|8|@]|9|@]|A|$]]|$1|B|3|-4|5|6|7|E|8|@]|9|@]|A|$]]]|C|$]]

<p>That's basically the whole point of an ID. :) IDs are specific, can only be used once per page. Classes can be used as pleased.</p>


blocks|key|425329|text|浏览器过去对此很宽松(很多年前css还很年轻的时候)，并允许多次使用ID。他们已经变得更加严格。|type|unstyled|depth|inlineStyleRanges|entityRanges|data|425330|但是，yes+ID必须是唯一的，并且只能使用一次。|425331|如果需要多次使用css格式，请使用CLASS。|425332|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>Browsers used to be lenient on this (many years ago when css was young) and allow the ID to be used more than once.  They have become more strict.</p>

<p>However, yes ID's are to be unique and only used once.</p>

<p>If you need to use css formatting more than once use CLASS.</p>


blocks|key|425421|text|在Javascript中，您只能使用ID引用一个元素。document.getElementById和jQuery的$选择器将只返回第一个匹配的元素。所以在多个元素上使用相同的ID是没有意义的。|type|unstyled|depth|inlineStyleRanges|offset|length|style|CODE|entityRanges|data|425422|entityMap^0|R|N|1M|1|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|$]]

<p>With Javascript, you can only reference to one element using ID. <code>document.getElementById</code> and jQuery's <code>$</code> selector will return only the first element matching. So it doesn't make sense using the same ID on multiple elements.</p>


blocks|key|425536|text|我补充这个问题，因为我觉得上面的任何一个问题都没有得到充分的回答，|type|unstyled|depth|inlineStyleRanges|entityRanges|data|425537|作为一点参考:我已经实现了非唯一id，所有的都工作得很好(在所有浏览器上)。重要的是，在编码时，我没有遇到任何css逻辑错误，这就是这个问题的关键所在(IMO)。在js中也没有遇到任何冲突(因为可以在类的上下文中收集id)。|425538|那么，为什么id必须是唯一的呢？显而易见的答案(如上所述和重申)是‘因为’标准‘是这样说的。对我来说，缺少的部分是为什么？|425539|也就是说，如果有人无意中使用了同一个id两次，那么到底是什么出了问题(或者理论上会出问题)？|425540|entityMap^0|0|0|0|0^^$0|@$1|2|3|4|5|6|7|J|8|@]|9|@]|A|$]]|$1|B|3|C|5|6|7|K|8|@]|9|@]|A|$]]|$1|D|3|E|5|6|7|L|8|@]|9|@]|A|$]]|$1|F|3|G|5|6|7|M|8|@]|9|@]|A|$]]|$1|H|3|-4|5|6|7|N|8|@]|9|@]|A|$]]]|I|$]]

<p>I'm adding to this question, because I feel it has not been answered adequately in any of the above,</p>
<p>As a point reference: I've implemented non-unique id's, and all works just fine (across all browsers). Importantly, when coding, I've not run into any css logic errors, which is where the rubber hits the road (IMO) on this question. Have also not run into any conflicts in js (as one can glean out id's in context with classes)</p>
<p>So, why do id's have to be unique? Obvious answer (as stated and re-stated above) is 'cause the 'standards' say so. The missing part for me is why?</p>
<p>i.e. what actually goes awry (or could theoretically go awry) if (heaven forbid) someone inadvertently used the same id twice?</p>


blocks|key|425642|text|这些天来所有浏览器的参考资料？|type|unstyled|depth|inlineStyleRanges|entityRanges|data|425643|使得div可以在这样的条件下被多次使用。|425644|没有规则要求它必须是唯一的。当所有的浏览器都明白：|425645|<script>div#some+{font-size:+20px}</script>
<div+id="some"><p>understand</p></div>
<div+id="some"><h1>me+too</h1></div>|code-block|syntax|javascript|425646|当您添加新样式的CSS代码时，您可以使用添加的样式。既然它甚至不应该是唯一的，它描述了相反的用途，所以制作更多的样式，但不制作更多的对象？你可以分配几个div对象，那么为什么他们不告诉你类必须是唯一的呢？这是因为该类不需要唯一值。这使得ID在法律术语中变得过时，如果不是唯一的话。|425647|<script>.some+{font-size:+25px}</script>
<div+class="some"><p>enter</p></div>
<div+class="some"><h1>enter</p></div>|425648|“当没有规则的时候，当一个规则被说出来的时候。那么规则就没有得到满足。它并不是固有的存在。只是在所有规则的幻觉中，它本应该存在，只是为了让生活变得更加艰难。”|425649|仅仅因为有些人说div必须是唯一的，这可能是对的，但至少从他们的专业角度来看，他们必须这么说。除非他们没有检查过现代浏览器，因为它们几乎从一开始就能够理解几个具有相同风格的不同div对象的代码。|425650|entityMap^0|0|0|0|0|0|0|0|0^^$0|@$1|2|3|4|5|6|7|U|8|@]|9|@]|A|$]]|$1|B|3|C|5|6|7|V|8|@]|9|@]|A|$]]|$1|D|3|E|5|6|7|W|8|@]|9|@]|A|$]]|$1|F|3|G|5|H|7|X|8|@]|9|@]|A|$I|J]]|$1|K|3|L|5|6|7|Y|8|@]|9|@]|A|$]]|$1|M|3|N|5|H|7|Z|8|@]|9|@]|A|$I|J]]|$1|O|3|P|5|6|7|10|8|@]|9|@]|A|$]]|$1|Q|3|R|5|6|7|11|8|@]|9|@]|A|$]]|$1|S|3|-4|5|6|7|12|8|@]|9|@]|A|$]]]|T|$]]

<p>The reference with all browsers these days?</p>
<p>Makes div possible in such terms of being used multiple times.</p>
<p>There is no rule that it must be unique. When all browsers understand:</p>
<pre><code>&lt;script&gt;div#some {font-size: 20px}&lt;/script&gt;
&lt;div id=&quot;some&quot;&gt;&lt;p&gt;understand&lt;/p&gt;&lt;/div&gt;
&lt;div id=&quot;some&quot;&gt;&lt;h1&gt;me too&lt;/h1&gt;&lt;/div&gt;
</code></pre>
<p>When you add new style CSS codes you have the possibility to use the addition of styles. Since that even is not supposed to be unique it describes the opposite use, so make more styles but do not make more objects? And as you can; assign several div objects, so why didn't they tell you that class must be unique? That's because the class does not need unique value. And that makes the ID in legal terms obsolete if not being unique.</p>
<pre><code>&lt;script&gt;.some {font-size: 25px}&lt;/script&gt;
&lt;div class=&quot;some&quot;&gt;&lt;p&gt;enter&lt;/p&gt;&lt;/div&gt;
&lt;div class=&quot;some&quot;&gt;&lt;h1&gt;enter&lt;/p&gt;&lt;/div&gt;
</code></pre>
<p>&quot;When there is no rule when a rule is said. Then the rule is not fulfilled. It's not inherent to exist. By only in the illusion of all rules that it should have existed only to make life much harder.&quot;</p>
<p>Just because some people say div must be unique, this might be right, but at least through their professional perspective to say it, they have to say it. Unless they didn't check the modern browsers, which from nearly the beginning were able to understand the code of several different div objects with the same style.</p>


<p>I am using jQuery and I am just wondering, does ID have to be always unique in the whole page? Class, I know, can be repeated as many times as you like, what about ID?</p>


Does ID have to be unique in the whole page?

jQuery

我正在使用jQuery，我只是在想，ID在整个页面中是否必须始终是唯一的？类，我知道，可以重复你喜欢的次数，那么ID呢？

问ID在整个页面中必须是唯一的吗？
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