blocks|key|2604672|text|元中的字符集|type|unstyled|depth|inlineStyleRanges|offset|length|style|BOLD|entityRanges|data|2604673|HTML告诉<meta+charset=“utf-8”>+(不那么草率地说:+HTML解析器)页面的编码是utf8。|CODE|2604674|JS没有内置的工具来在不同的字符串编码之间切换-它始终是utf-16。|2604675|渐近界|2604676|我不认为编码转换会有O(n)方面的损失。每当这种编码更改到期时，就已经有了一个O(n)操作:读/写数据流。因此，每个二进制八位数上的任何固定数量的操作仍然是O(n)。编码更改只需要本地知识，即。仅具有固定长度的前瞻窗口，因此可以以O(1)的代价并入流读/写代码中。|2604677|您可以争辩说，空间惩罚是O(n)，尽管如果需要以任何标准编码存储字符串(即。在没有压缩的情况下)，移动到utf-16意味着最大因子为2，从而保持在O(n)界限内。|2604678|常量因子|2604679|即使关注的是最小化隐藏在O(n)表示法中的恒定因素，编码更改也会产生适度的影响，至少在时间域中是这样。对于大部分(西方)文本数据，以utf-8格式写入/读取utf-16流意味着每隔一秒跳过一次八位字节/插入空八位字节。与与套接字或文件系统连接所产生的开销和延迟相比，这种性能影响相形见绌。|2604680|当然，存储是不同的，尽管今天的存储相对便宜，并且2的上限仍然有效。从32位移动到64位对数字表示和指针有更高的内存影响。|2604681|entityMap^0|3|3|0|0|1M|6|M|0|0|Z|0|0|3|0|0|3O|A|4|13|4|26|4|37|4|0|0|29|C|4|21|4|0|0|4|0|0|40|C|4|0|0|1O|0^^$0|@$1|2|3|4|5|6|7|Y|8|@$9|Z|A|10|B|C]]|D|@]|E|$]]|$1|F|3|G|5|6|7|11|8|@$9|12|A|13|B|C]|$9|14|A|15|B|H]]|D|@]|E|$]]|$1|I|3|J|5|6|7|16|8|@$9|17|A|18|B|C]]|D|@]|E|$]]|$1|K|3|L|5|6|7|19|8|@$9|1A|A|1B|B|C]]|D|@]|E|$]]|$1|M|3|N|5|6|7|1C|8|@$9|1D|A|1E|B|C]|$9|1F|A|1G|B|H]|$9|1H|A|1I|B|H]|$9|1J|A|1K|B|H]|$9|1L|A|1M|B|H]]|D|@]|E|$]]|$1|O|3|P|5|6|7|1N|8|@$9|1O|A|1P|B|C]|$9|1Q|A|1R|B|H]|$9|1S|A|1T|B|H]]|D|@]|E|$]]|$1|Q|3|R|5|6|7|1U|8|@$9|1V|A|1W|B|C]]|D|@]|E|$]]|$1|S|3|T|5|6|7|1X|8|@$9|1Y|A|1Z|B|C]|$9|20|A|21|B|H]]|D|@]|E|$]]|$1|U|3|V|5|6|7|22|8|@$9|23|A|24|B|C]]|D|@]|E|$]]|$1|W|3|-4|5|6|7|25|8|@]|D|@]|E|$]]]|X|$]]

Charset in meta

The <code>&lt;meta charset=“utf-8”&gt;</code> tag tells HTML (less sloppily: the HTML parser) that the encoding of the page is utf8.

JS does not have a built-in facility to switch between different encondings of strings - it is always utf-16.

Asymptotic bounds

I do not think that there is a <code>O(n)</code> penalty for encoding conversions. Whenever this kind of encoding change is due, there already is an <code>O(n)</code> operation: reading/writing the data stream. So any fixed number of operations on each octet would still be <code>O(n)</code>. Encoding change requires local knowledge only, ie. a look-ahead window of fixed length only, and can thus be incorporated in the stream read/write code with a penalty of <code>O(1)</code>.

You could argue that the space penalty is <code>O(n)</code>, though if there is the need to store the string in any standard encoding (ie. without compression), the move to utf-16 means a factor of 2 at max thus staying within the <code>O(n)</code> bound.

Constant factors

Even if the concern is minimizing the constant factors hidden in <code>O(n)</code> notation encoding change have a modest impact, in the time domain at least. Writing/reading a utf-16 stream as utf-8 for the most part of (Western) textual data means skipping every second octet / inserting null octets. That performance hit pales in comparison with the overhead and the latency stemming from interfacing with a socket or the file system.

Storage is different, of course, though storage is comparatively cheap today and the upper bound of 2 still holds. The move from 32 to 64 bit has a higher memeory impact wrt to number representations and pointers.

blocks|key|87302|text|JavaScript使用UTF-16|type|unstyled|depth|inlineStyleRanges|entityRanges|data|87303|HTML5使用UTF-8|87304|您的meta标记设置适用于HTML5编码，这是可选的，因为大多数现代浏览器都知道HTML5是UTF8。但是，它与JavaScript编码无关，也不会更改或影响JavaScript，只会告诉它使用UTF8编码对页面进行解码。|87305|大多数现代Javascript引擎的工作方式是，它们确实读取UTF-8脚本、HTML标记和页面文本，并将其解码为UTF-16。但由于速度和其他原因，它们通常以原生形式存储第一个ASCII集(英语字符和数字)，或者像UTF-8或您的网页那样以一个字节的形式存储。这不是一个硬性的规则。因此，由Javascript读取和存储的HTML标签可能仍然存储在一个字节中，而不是V8+-16。|87306|就存储在UTF-8中的大多数ASCII字符而言，这些脚本引擎背后发生的事情并不是您应该担心的。只有在流式传输更复杂的Unicode字符的上层“平面”时才会遇到问题。我读到过，Javascript存储和编码的UTF-16特征是可变的。在我看来，在你熟悉上层Unicode语言和Javascript中的字符集操作之前，这并不是大多数web开发人员需要担心的事情。这就是Node和许多开源引擎在解码和编码UTF-8和UTF-16方面所面临的困难，因为它们依赖于Javascripting引擎。|87307|同样，因为现在一切都转向UTF-8编码(其中1-4字节可用于编码完整的Unicode字符集，而UTF-16从2字节集开始并向上)，您将看到Javascript处理所有UTF-8到UTF-16的解码，然后作为一个非常无缝的过程返回，其中有很多应急措施。|87308|BTW....the的方式脚本引擎读取或弄清楚你的Javascript文件在UTF8编码，是Javascript首先侦听mime类型或“内容类型”和字符集的头部来自服务器，以查看所有的网页文件应该解码。如前所述，现在HTML5中几乎总是使用UTF-8。如果无法确定类型，则接下来检查脚本的<script>标记及其mime类型和/或字符集的自定义类型属性，以查看javascript源文件是否设置了该类型。在大多数情况下，这些都会丢失。最后，它检查网页的meta标签字符集，如果是UTF-8，或者如果使用了HTML5，则假定为UTF-8。脚本文件上也有“字节顺序标记”，很可能是UTF-8。即使它是用ASCII或者说拉丁文-1编码的，也可以直接翻译成UTF-8。一旦知道了编码，Javascript就会解码这些位，并将它们编码成如上所述的自己的2字节集。|offset|length|style|CODE|87309|在一天结束的时候，引擎为你做了很好的谈判工作。|87310|entityMap^0|0|0|0|0|0|0|40|8|0|0^^$0|@$1|2|3|4|5|6|7|V|8|@]|9|@]|A|$]]|$1|B|3|C|5|6|7|W|8|@]|9|@]|A|$]]|$1|D|3|E|5|6|7|X|8|@]|9|@]|A|$]]|$1|F|3|G|5|6|7|Y|8|@]|9|@]|A|$]]|$1|H|3|I|5|6|7|Z|8|@]|9|@]|A|$]]|$1|J|3|K|5|6|7|10|8|@]|9|@]|A|$]]|$1|L|3|M|5|6|7|11|8|@$N|12|O|13|P|Q]]|9|@]|A|$]]|$1|R|3|S|5|6|7|14|8|@]|9|@]|A|$]]|$1|T|3|-4|5|6|7|15|8|@]|9|@]|A|$]]]|U|$]]

JavaScript uses UTF-16
HTML5 uses UTF-8
Your meta tag setting applies to HTML5 encoding, which is optional as most modern browsers know HTML5 is UTF-8. It has nothing to do with JavaScript encoding, however, and does not change or affect JavaScript except to tell it to decode your page using UTF-8 encoding.
The way most modern Javascript engines work is YES they do read and decode UTF-8 script, HTML markup, and page text into UTF-16. But for speed and other reasons, they often store the first ASCII set (English characters and numbers) in its native form, or as one byte just as UTF-8 or your web page does. Its not a hard and fast rule. So HTML tags read and stored by Javascript in say Chrome's V8 javascript engine might still store them in one byte, not UTF-16.
What is happening under the covers of these scripting engines in terms of most ASCII characters stored in UTF-8 isn't something you should worry about. You only run into issues when streaming more complex upper &quot;planes&quot; of Unicode characters. The UTF-16 characteristics of Javascript storage and encoding are variable, I have read. Its not something most web developers need to worry about, in my opinion, until you get into upper level Unicode languages and character set manipulation in Javascript. That is what Node and many open source engines have struggled at in terms of decoding and encoding UTF-8 and UTF-16 because of their reliance on Javascripting engines.
Again, because everything is moving towards UTF-8 encoding now (where 1-4 bytes are optionally used to encode the complete Unicode character set versus UTF-16 which starts at 2-bytes sets and goes up) you will see Javascript handle all that decoding of UTF-8 into UTF-16 and back out as a pretty seamless process with lots of contingency in place.
BTW....the way scripting engines read or figure out your Javascript files encoded in UTF-8, is Javascript first listens to the mime type or &quot;content-type&quot; and charset in the HTTP header coming from the server to see what all the web page files should be decoded from. As mentioned that's almost always UTF-8 now in HTML5. If it cannot determine the type it next checks your script's <code>&lt;script&gt;</code> tag and its custom type attributes for both mime type and/or charset to see what if your javascript source file has set that type. In most cases those are missing. Lastly, it checks the web pages meta tag charset which is either UTF-8 or if HTML5 is used, it assumes UTF-8. There is also the &quot;byte order mark&quot; on the script file which likely is UTF-8. Even if its encoded in ASCII or say Latin-1 that translates directly into UTF-8, anyway. Once the encoding is known, Javascript then decodes the bits and encodes them into its own 2-byte set as mentioned above.
At the end of the day the engines do a good job of negotiating all this for you.

I have been trying to understanding why the need for encoding/decoding to UTF-8 happens all over the place in JavaScript land, and learned that JavaScript uses UTF-16 encoding.

<a href="https://kev.inburke.com/kevin/node-js-string-encoding/" rel="nofollow noreferrer">Let’s talk about Javascript string encoding</a>

So I'm assuming that's why a library such as <a href="https://github.com/mathiasbynens/utf8.js" rel="nofollow noreferrer">utf8.js</a> exists, to convert between UTF-16 and UTF-8.

But then at the end he provides some insights:

<blockquote>
 Encoding in Node is extremely confusing, and difficult to get right. It helps, though, when you realize that Javascript string types will always be encoded as UTF-16, and most of the other places strings in RAM interact with sockets, files, or byte arrays, the string gets re-encoded as UTF-8.
 
 This is all massively inefficient, of course. Most strings are representable as UTF-8, and using two bytes to represent their characters means you are using more memory than you need to, as well as paying an O(n) tax to re-encode the string any time you encounter a HTTP or filesystem boundary.
</blockquote>

That reminded me of the <a href="https://stackoverflow.com/questions/16505367/what-happens-when-we-dont-specify-meta-charset-utf-8"><code>&lt;meta charset=“utf-8”&gt;</code></a> in the HTML <code>&lt;head&gt;</code>, which I never really thought too much about, other than "you need this to get text working properly".

Now I'm wondering, which this question is about, if that <code>&lt;meta charset=“utf-8”&gt;</code> tag tells JavaScript to do UTF-8 encoding. That would then mean that when you create strings in JavaScript, they would be UTF-8 encoded rather than UTF-16. Or if I'm wrong there, what exactly it is doing. If it is telling JavaScript to use UTF-8 encoding instead of UTF-16 (which I guess would be considered the "default"), then that would mean you don't need to be paying that <code>O(n)</code> tax over doing conversions between UTF-8 and UTF-16, which would mean a performance improvement. Wondering if I am understanding correctly, or if not, what I am missing.

If <meta charset=“utf-8”> means that JavaScript is using utf-8 encoding instead of utf-16

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

云原生构建

TAPD 敏捷项目管理

Cloud Studio

SDK中心

API中心

命令行工具

涵盖代码开发、场景应用、自动测试全流程，助你从零构建专属AI助手

一站式MCP教程库，解锁AI应用新玩法

我一直在尝试理解为什么在JavaScript的世界里到处都需要使用UTF-8编码/解码，并且了解到JavaScript使用UTF-16编码。所以我假设这就是像这样的库存在的原因，它可以在UTF-16和UTF-8之间进行转换。但在最后，他提供了一些见解：Node中的编码非常令人困惑，而且很难正确使用。但是，当您意识到Ja...

问如果表示JavaScript正在使用utf-8编码而不是utf-16
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

问如果表示JavaScript正在使用utf-8编码而不是utf-16EN

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

问如果表示JavaScript正在使用utf-8编码而不是utf-16
EN