blocks|key|1770515|text|几年过去了，现在你可以原生地做了|type|unstyled|depth|inlineStyleRanges|entityRanges|data|1770516|(new+TextEncoder().encode('foo')).length|code-block|syntax|javascript|1770517|请注意，IE不支持它(您可以使用use+a+polyfill+)。|offset|length|1770518|MDN+documentation|1770519|Standard+specifications|1770520|entityMap|0|LINK|mutability|MUTABLE|url|https://github.com/inexorabletash/text-encoding|1|https://developer.mozilla.org/en-US/docs/Web/API/TextEncoder|2|https://encoding.spec.whatwg.org/^0|0|0|G|E|0|0|0|H|1|0|0|N|2|0^^$0|@$1|2|3|4|5|6|7|10|8|@]|9|@]|A|$]]|$1|B|3|C|5|D|7|11|8|@]|9|@]|A|$E|F]]|$1|G|3|H|5|6|7|12|8|@]|9|@$I|13|J|14|1|15]]|A|$]]|$1|K|3|L|5|6|7|16|8|@]|9|@$I|17|J|18|1|19]]|A|$]]|$1|M|3|N|5|6|7|1A|8|@]|9|@$I|1B|J|1C|1|1D]]|A|$]]|$1|O|3|-4|5|6|7|1E|8|@]|9|@]|A|$]]]|P|$Q|$5|R|S|T|A|$U|V]]|W|$5|R|S|T|A|$U|X]]|Y|$5|R|S|T|A|$U|Z]]]]

Years passed and nowadays you can do it natively
<pre><code>(new TextEncoder().encode('foo')).length
</code></pre>
Note that it's not supported by IE (you may <a href="https://github.com/inexorabletash/text-encoding" rel="noreferrer">use a polyfill</a> for that).
<a href="https://developer.mozilla.org/en-US/docs/Web/API/TextEncoder" rel="noreferrer">MDN documentation</a>
<a href="https://encoding.spec.whatwg.org/" rel="noreferrer">Standard specifications</a>

blocks|key|1770578|text|对于简单的UTF8编码，其兼容性比TextEncoder稍好，Blob可以做到这一点。不能在非常老的浏览器中工作。|type|unstyled|depth|inlineStyleRanges|offset|length|style|CODE|entityRanges|data|1770579|new+Blob([""]).size;+//+->+4++|code-block|syntax|javascript|1770580|entityMap^0|H|B|0|0^^$0|@$1|2|3|4|5|6|7|M|8|@$9|N|A|O|B|C]]|D|@]|E|$]]|$1|F|3|G|5|H|7|P|8|@]|D|@]|E|$I|J]]|$1|K|3|-4|5|6|7|Q|8|@]|D|@]|E|$]]]|L|$]]

For simple UTF-8 encoding, with slightly better compatibility than <code>TextEncoder</code>, Blob does the trick. Won't work in very old browsers though.

<pre><code>new Blob([""]).size; // -&gt; 4 
</code></pre>

blocks|key|1983893|text|此函数将返回您传递给它的任何UTF-8字符串的字节大小。|type|unstyled|depth|inlineStyleRanges|entityRanges|data|1983894|function+byteCount(s)+{
++++return+encodeURI(s).split(/%25..%7C./).length+-+1;
}|code-block|syntax|javascript|1983895|Source|offset|length|1983896|entityMap|0|LINK|mutability|MUTABLE|url|https://gist.github.com/1010324^0|0|0|0|6|0|0^^$0|@$1|2|3|4|5|6|7|S|8|@]|9|@]|A|$]]|$1|B|3|C|5|D|7|T|8|@]|9|@]|A|$E|F]]|$1|G|3|H|5|6|7|U|8|@]|9|@$I|V|J|W|1|X]]|A|$]]|$1|K|3|-4|5|6|7|Y|8|@]|9|@]|A|$]]]|L|$M|$5|N|O|P|A|$Q|R]]]]

This function will return the byte size of any UTF-8 string you pass to it.

<pre class="lang-js prettyprint-override"><code>function byteCount(s) {
 return encodeURI(s).split(/%..|./).length - 1;
}
</code></pre>

<a href="https://gist.github.com/1010324" rel="noreferrer">Source</a>

blocks|key|1984054|text|使用Buffer+(仅适用于NodeJS)的另一种非常简单的方法：|type|unstyled|depth|inlineStyleRanges|offset|length|style|CODE|entityRanges|data|1984055|Buffer.byteLength(string,+'utf8')

Buffer.from(string).length|code-block|syntax|javascript|1984056|entityMap^0|2|6|0|0^^$0|@$1|2|3|4|5|6|7|M|8|@$9|N|A|O|B|C]]|D|@]|E|$]]|$1|F|3|G|5|H|7|P|8|@]|D|@]|E|$I|J]]|$1|K|3|-4|5|6|7|Q|8|@]|D|@]|E|$]]]|L|$]]

Another very simple approach using <code>Buffer</code> (only for NodeJS):

<pre><code>Buffer.byteLength(string, 'utf8')

Buffer.from(string).length
</code></pre>

blocks|key|1770780|text|我在Firefox中比较了这里建议的一些方法的速度。|type|unstyled|depth|inlineStyleRanges|entityRanges|data|1770781|我使用的字符串包含以下字符:œ‘®†used+?ˆøπ，˚∆·©ƒ∂？Ω≈ç√∫˜µ≤|1770782|所有结果都是3次运行的平均值。时间以毫秒为单位。请注意，所有URIEncoding方法的行为都相似，并且都有极端的结果，所以我只包含了一个方法。|1770783|虽然字符串的大小有一些波动，但charCode方法(lovasoa和fuweichin)的执行速度相似，总体上也是最快的，其中fuweichin的charCode方法最快。Blob和TextEncoder方法的执行方式彼此相似。一般来说，charCode方法比Blob和TextEncoder方法快75%25左右。URIEncoding方法基本上是不可接受的。|1770784|以下是我得到的结果：|1770785|大小6.4+*+10%5E6字节：|1770786|Lauri+Oherd+–+URIEncoding:+++++6400000++++et:+796
lovasoa+–+charCode:++++++++++++6400000++++et:+15
fuweichin+–+charCode2:+++++++++6400000++++et:+16
simap+–+Blob:++++++++++++++++++6400000++++et:+26
Riccardo+Galli+–+TextEncoder:++6400000++++et:+23|code-block|syntax|javascript|1770787|大小为19.2+*+10%5E6字节:+Blob在这里做了一件奇怪的事情。|1770788|Lauri+Oherd+–+URIEncoding:+++++19200000++++et:+2322
lovasoa+–+charCode:++++++++++++19200000++++et:+42
fuweichin+–+charCode2:+++++++++19200000++++et:+45
simap+–+Blob:++++++++++++++++++19200000++++et:+169
Riccardo+Galli+–+TextEncoder:++19200000++++et:+70|1770789|大小为64+*+10%5E6字节：|1770790|Lauri+Oherd+–+URIEncoding:+++++64000000++++et:+12565
lovasoa+–+charCode:++++++++++++64000000++++et:+138
fuweichin+–+charCode2:+++++++++64000000++++et:+133
simap+–+Blob:++++++++++++++++++64000000++++et:+231
Riccardo+Galli+–+TextEncoder:++64000000++++et:+211|1770791|大小为192+*+10%5E6字节:+URIEncoding方法此时冻结浏览器。|1770792|lovasoa+–+charCode:++++++++++++192000000++++et:+754
fuweichin+–+charCode2:+++++++++192000000++++et:+480
simap+–+Blob:++++++++++++++++++192000000++++et:+701
Riccardo+Galli+–+TextEncoder:++192000000++++et:+654|1770793|大小为640+*+10%5E6字节：|1770794|lovasoa+–+charCode:++++++++++++640000000++++et:+2417
fuweichin+–+charCode2:+++++++++640000000++++et:+1602
simap+–+Blob:++++++++++++++++++640000000++++et:+2492
Riccardo+Galli+–+TextEncoder:++640000000++++et:+2338|1770795|大小为1280+*+10%5E6字节:+Blob和TextEncoder方法开始在这里碰壁。|1770796|lovasoa+–+charCode:++++++++++++1280000000++++et:+4780
fuweichin+–+charCode2:+++++++++1280000000++++et:+3177
simap+–+Blob:++++++++++++++++++1280000000++++et:+6588
Riccardo+Galli+–+TextEncoder:++1280000000++++et:+5074|1770797|大小为1920+*+10%5E6字节：|1770798|lovasoa+–+charCode:++++++++++++1920000000++++et:+7465
fuweichin+–+charCode2:+++++++++1920000000++++et:+4968
JavaScript+error:+file:///Users/xxx/Desktop/test.html,+line+74:+NS_ERROR_OUT_OF_MEMORY:|1770799|代码如下：|1770800|​|1770801|function+byteLengthURIEncoding(str)+{
++return+encodeURI(str).split(/%25..%7C./).length+-+1;
}

function+byteLengthCharCode(str)+{
++//+returns+the+byte+length+of+an+utf8+string
++var+s+=+str.length;
++for+(var+i=str.length-1;+i>=0;+i--)+{
++++var+code+=+str.charCodeAt(i);
++++if+(code+>+0x7f+&&+code+<=+0x7ff)+s%2B%2B;
++++else+if+(code+>+0x7ff+&&+code+<=+0xffff)+s%2B=2;
++++if+(code+>=+0xDC00+&&+code+<=+0xDFFF)+i--;+//trail+surrogate
++}
++return+s;
}

function+byteLengthCharCode2(s){
++//assuming+the+String+is+UCS-2(aka+UTF-16)+encoded
++var+n=0;
++for(var+i=0,l=s.length;+i<l;+i%2B%2B){
++++var+hi=s.charCodeAt(i);
++++if(hi<0x0080){+//[0x0000,+0x007F]
++++++n%2B=1;
++++}else+if(hi<0x0800){+//[0x0080,+0x07FF]
++++++n%2B=2;
++++}else+if(hi<0xD800){+//[0x0800,+0xD7FF]
++++++n%2B=3;
++++}else+if(hi<0xDC00){+//[0xD800,+0xDBFF]
++++++var+lo=s.charCodeAt(%2B%2Bi);
++++++if(i<l&&lo>=0xDC00&&lo<=0xDFFF){+//followed+by+[0xDC00,+0xDFFF]
++++++++n%2B=4;
++++++}else{
++++++++throw+new+Error("UCS-2+String+malformed");
++++++}
++++}else+if(hi<0xE000){+//[0xDC00,+0xDFFF]
++++++throw+new+Error("UCS-2+String+malformed");
++++}else{+//[0xE000,+0xFFFF]
++++++n%2B=3;
++++}
++}
++return+n;
}

function+byteLengthBlob(str)+{
++return+new+Blob([str]).size;
}

function+byteLengthTE(str)+{
++return+(new+TextEncoder().encode(str)).length;
}

var+sample+=+"œ´®†¥¨ˆøπ¬˚∆˙©ƒ∂ßåΩ≈ç√∫˜µ≤i";
var+string+=+"";

//+Adjust+multiplier+to+change+length+of+string.
let+mult+=+1000000;

for+(var+i+=+0;+i+<+mult;+i%2B%2B)+{
++string+%2B=+sample;
}

let+t0;

try+{
++t0+=+Date.now();
++console.log("Lauri+Oherd+–+URIEncoding:+++"+%2B+byteLengthURIEncoding(string)+%2B+"++++et:+"+%2B+(Date.now()+-+t0));
}+catch(e)+{}

t0+=+Date.now();
console.log("lovasoa+–+charCode:++++++++++++"+%2B+byteLengthCharCode(string)+%2B+"++++et:+"+%2B+(Date.now()+-+t0));

t0+=+Date.now();
console.log("fuweichin+–+charCode2:+++++++++"+%2B+byteLengthCharCode2(string)+%2B+"++++et:+"+%2B+(Date.now()+-+t0));

t0+=+Date.now();
console.log("simap+–+Blob:++++++++++++++++++"+%2B+byteLengthBlob(string)+%2B+"++++et:+"+%2B+(Date.now()+-+t0));

t0+=+Date.now();
console.log("Riccardo+Galli+–+TextEncoder:++"+%2B+byteLengthTE(string)+%2B+"++++et:+"+%2B+(Date.now()+-+t0));|1770802|1770803|entityMap^0|0|0|0|0|0|0|0|0|0|0|0|0|0|0|0|0|0|0|0|0|0|0|0^^$0|@$1|2|3|4|5|6|7|1N|8|@]|9|@]|A|$]]|$1|B|3|C|5|6|7|1O|8|@]|9|@]|A|$]]|$1|D|3|E|5|6|7|1P|8|@]|9|@]|A|$]]|$1|F|3|G|5|6|7|1Q|8|@]|9|@]|A|$]]|$1|H|3|I|5|6|7|1R|8|@]|9|@]|A|$]]|$1|J|3|K|5|6|7|1S|8|@]|9|@]|A|$]]|$1|L|3|M|5|N|7|1T|8|@]|9|@]|A|$O|P]]|$1|Q|3|R|5|6|7|1U|8|@]|9|@]|A|$]]|$1|S|3|T|5|N|7|1V|8|@]|9|@]|A|$O|P]]|$1|U|3|V|5|6|7|1W|8|@]|9|@]|A|$]]|$1|W|3|X|5|N|7|1X|8|@]|9|@]|A|$O|P]]|$1|Y|3|Z|5|6|7|1Y|8|@]|9|@]|A|$]]|$1|10|3|11|5|N|7|1Z|8|@]|9|@]|A|$O|P]]|$1|12|3|13|5|6|7|20|8|@]|9|@]|A|$]]|$1|14|3|15|5|N|7|21|8|@]|9|@]|A|$O|P]]|$1|16|3|17|5|6|7|22|8|@]|9|@]|A|$]]|$1|18|3|19|5|N|7|23|8|@]|9|@]|A|$O|P]]|$1|1A|3|1B|5|6|7|24|8|@]|9|@]|A|$]]|$1|1C|3|1D|5|N|7|25|8|@]|9|@]|A|$O|P]]|$1|1E|3|1F|5|6|7|26|8|@]|9|@]|A|$]]|$1|1G|3|1H|5|6|7|27|8|@]|9|@]|A|$]]|$1|1I|3|1J|5|N|7|28|8|@]|9|@]|A|$O|P]]|$1|1K|3|1H|5|6|7|29|8|@]|9|@]|A|$]]|$1|1L|3|-4|5|6|7|2A|8|@]|9|@]|A|$]]]|1M|$]]

I compared some of the methods suggested here in Firefox for speed.
The string I used contained the following characters:
œ´®†¥¨ˆøπ¬˚∆˙©ƒ∂ßåΩ≈ç√∫˜µ≤
All results are averages of 3 runs each. Times are in milliseconds. Note that all URIEncoding methods behaved similarly and had extreme results, so I only included one.
While there are some fluctuations based on the size of the string, the charCode methods (lovasoa and fuweichin) both perform similarly and the fastest overall, with fuweichin's charCode method the fastest. The Blob and TextEncoder methods performed similarly to each other. Generally the charCode methods were about 75% faster than the Blob and TextEncoder methods. The URIEncoding method was basically unacceptable.
Here are the results I got:
Size 6.4 * 10^6 bytes:
<pre><code>Lauri Oherd – URIEncoding: 6400000 et: 796
lovasoa – charCode: 6400000 et: 15
fuweichin – charCode2: 6400000 et: 16
simap – Blob: 6400000 et: 26
Riccardo Galli – TextEncoder: 6400000 et: 23
</code></pre>
Size 19.2 * 10^6 bytes:
Blob does kind of a weird thing here.
<pre><code>Lauri Oherd – URIEncoding: 19200000 et: 2322
lovasoa – charCode: 19200000 et: 42
fuweichin – charCode2: 19200000 et: 45
simap – Blob: 19200000 et: 169
Riccardo Galli – TextEncoder: 19200000 et: 70
</code></pre>
Size 64 * 10^6 bytes:
<pre><code>Lauri Oherd – URIEncoding: 64000000 et: 12565
lovasoa – charCode: 64000000 et: 138
fuweichin – charCode2: 64000000 et: 133
simap – Blob: 64000000 et: 231
Riccardo Galli – TextEncoder: 64000000 et: 211
</code></pre>
Size 192 * 10^6 bytes:
URIEncoding methods freezes browser at this point.
<pre><code>lovasoa – charCode: 192000000 et: 754
fuweichin – charCode2: 192000000 et: 480
simap – Blob: 192000000 et: 701
Riccardo Galli – TextEncoder: 192000000 et: 654
</code></pre>
Size 640 * 10^6 bytes:
<pre><code>lovasoa – charCode: 640000000 et: 2417
fuweichin – charCode2: 640000000 et: 1602
simap – Blob: 640000000 et: 2492
Riccardo Galli – TextEncoder: 640000000 et: 2338
</code></pre>
Size 1280 * 10^6 bytes:
Blob &amp; TextEncoder methods are starting to hit the wall here.
<pre><code>lovasoa – charCode: 1280000000 et: 4780
fuweichin – charCode2: 1280000000 et: 3177
simap – Blob: 1280000000 et: 6588
Riccardo Galli – TextEncoder: 1280000000 et: 5074
</code></pre>
Size 1920 * 10^6 bytes:
<pre><code>lovasoa – charCode: 1920000000 et: 7465
fuweichin – charCode2: 1920000000 et: 4968
JavaScript error: file:///Users/xxx/Desktop/test.html, line 74: NS_ERROR_OUT_OF_MEMORY:
</code></pre>
Here is the code:
<div class="snippet" data-lang="js" data-hide="false" data-console="true" data-babel="false">
<div class="snippet-code">
<pre class="snippet-code-js lang-js prettyprint-override"><code>function byteLengthURIEncoding(str) {
 return encodeURI(str).split(/%..|./).length - 1;
}

function byteLengthCharCode(str) {
 // returns the byte length of an utf8 string
 var s = str.length;
 for (var i=str.length-1; i&gt;=0; i--) {
 var code = str.charCodeAt(i);
 if (code &gt; 0x7f &amp;&amp; code &lt;= 0x7ff) s++;
 else if (code &gt; 0x7ff &amp;&amp; code &lt;= 0xffff) s+=2;
 if (code &gt;= 0xDC00 &amp;&amp; code &lt;= 0xDFFF) i--; //trail surrogate
 }
 return s;
}

function byteLengthCharCode2(s){
 //assuming the String is UCS-2(aka UTF-16) encoded
 var n=0;
 for(var i=0,l=s.length; i&lt;l; i++){
 var hi=s.charCodeAt(i);
 if(hi&lt;0x0080){ //[0x0000, 0x007F]
 n+=1;
 }else if(hi&lt;0x0800){ //[0x0080, 0x07FF]
 n+=2;
 }else if(hi&lt;0xD800){ //[0x0800, 0xD7FF]
 n+=3;
 }else if(hi&lt;0xDC00){ //[0xD800, 0xDBFF]
 var lo=s.charCodeAt(++i);
 if(i&lt;l&amp;&amp;lo&gt;=0xDC00&amp;&amp;lo&lt;=0xDFFF){ //followed by [0xDC00, 0xDFFF]
 n+=4;
 }else{
 throw new Error("UCS-2 String malformed");
 }
 }else if(hi&lt;0xE000){ //[0xDC00, 0xDFFF]
 throw new Error("UCS-2 String malformed");
 }else{ //[0xE000, 0xFFFF]
 n+=3;
 }
 }
 return n;
}

function byteLengthBlob(str) {
 return new Blob([str]).size;
}

function byteLengthTE(str) {
 return (new TextEncoder().encode(str)).length;
}

var sample = "œ´®†¥¨ˆøπ¬˚∆˙©ƒ∂ßåΩ≈ç√∫˜µ≤i";
var string = "";

// Adjust multiplier to change length of string.
let mult = 1000000;

for (var i = 0; i &lt; mult; i++) {
 string += sample;
}

let t0;

try {
 t0 = Date.now();
 console.log("Lauri Oherd – URIEncoding: " + byteLengthURIEncoding(string) + " et: " + (Date.now() - t0));
} catch(e) {}

t0 = Date.now();
console.log("lovasoa – charCode: " + byteLengthCharCode(string) + " et: " + (Date.now() - t0));

t0 = Date.now();
console.log("fuweichin – charCode2: " + byteLengthCharCode2(string) + " et: " + (Date.now() - t0));

t0 = Date.now();
console.log("simap – Blob: " + byteLengthBlob(string) + " et: " + (Date.now() - t0));

t0 = Date.now();
console.log("Riccardo Galli – TextEncoder: " + byteLengthTE(string) + " et: " + (Date.now() - t0));</code></pre>
</div>
</div>

blocks|key|1770363|text|实际上，我知道问题出在哪里了。要使代码正常工作，页面<head>应具有以下标记：|type|unstyled|depth|inlineStyleRanges|offset|length|style|CODE|entityRanges|data|1770364|<meta+http-equiv="Content-Type"+content="text/html;+charset=utf-8"+/>|code-block|syntax|javascript|1770365|或者，正如评论中所建议的，如果服务器发送HTTP+Content-Encoding报头，它也应该可以工作。|1770366|那么来自不同浏览器的结果是一致的。|1770367|下面是一个示例：|1770368|<html>
<head>
++<meta+http-equiv="Content-Type"+content="text/html;+charset=utf-8"+/>+
++<title>mini+string+length+test</title>
</head>
<body>

<script+type="text/javascript">
document.write('<div+style="font-size:100px">'+
++++%2B+(unescape(encodeURIComponent("ЭЭХ!+Naïve?")).length)+%2B+'</div>'
++);
</script>
</body>
</html>|1770369|注意:我怀疑指定任何(准确的)编码都可以解决编码问题。我需要UTF-8，这只是个巧合。|1770370|entityMap^0|Q|6|0|0|P|G|0|0|0|0|0^^$0|@$1|2|3|4|5|6|7|W|8|@$9|X|A|Y|B|C]]|D|@]|E|$]]|$1|F|3|G|5|H|7|Z|8|@]|D|@]|E|$I|J]]|$1|K|3|L|5|6|7|10|8|@$9|11|A|12|B|C]]|D|@]|E|$]]|$1|M|3|N|5|6|7|13|8|@]|D|@]|E|$]]|$1|O|3|P|5|6|7|14|8|@]|D|@]|E|$]]|$1|Q|3|R|5|H|7|15|8|@]|D|@]|E|$I|J]]|$1|S|3|T|5|6|7|16|8|@]|D|@]|E|$]]|$1|U|3|-4|5|6|7|17|8|@]|D|@]|E|$]]]|V|$]]

Actually, I figured out what's wrong. For the code to work the page <code>&lt;head&gt;</code> should have this tag:

<pre><code>&lt;meta http-equiv="Content-Type" content="text/html; charset=utf-8" /&gt;
</code></pre>

Or, as suggested in comments, if server sends HTTP <code>Content-Encoding</code> header, it should work as well.

Then results from different browsers are consistent.

Here is an example: 

<pre><code>&lt;html&gt;
&lt;head&gt;
 &lt;meta http-equiv="Content-Type" content="text/html; charset=utf-8" /&gt; 
 &lt;title&gt;mini string length test&lt;/title&gt;
&lt;/head&gt;
&lt;body&gt;

&lt;script type="text/javascript"&gt;
document.write('&lt;div style="font-size:100px"&gt;' 
 + (unescape(encodeURIComponent("ЭЭХ! Naïve?")).length) + '&lt;/div&gt;'
 );
&lt;/script&gt;
&lt;/body&gt;
&lt;/html&gt;
</code></pre>

Note: I suspect that specifying any (accurate) encoding would fix the encoding problem. It is just a coincidence that I need UTF-8.

blocks|key|1770653|text|在NodeJS中，Buffer.byteLength是专门用于此目的的方法：|type|unstyled|depth|inlineStyleRanges|offset|length|style|CODE|entityRanges|data|1770654|let+strLengthInBytes+=+Buffer.byteLength(str);+//+str+is+UTF-8|code-block|syntax|javascript|1770655|请注意，默认情况下，该方法假定字符串为UTF-8编码。如果需要不同的编码，则将其作为第二个参数传递。|1770656|entityMap|0|LINK|mutability|MUTABLE|url|https://nodejs.org/api/buffer.html#buffer_class_method_buffer_bytelength_string_encoding^0|9|H|9|H|0|0|0|0^^$0|@$1|2|3|4|5|6|7|U|8|@$9|V|A|W|B|C]]|D|@$9|X|A|Y|1|Z]]|E|$]]|$1|F|3|G|5|H|7|10|8|@]|D|@]|E|$I|J]]|$1|K|3|L|5|6|7|11|8|@]|D|@]|E|$]]|$1|M|3|-4|5|6|7|12|8|@]|D|@]|E|$]]]|N|$O|$5|P|Q|R|E|$S|T]]]]

In NodeJS, <a href="https://nodejs.org/api/buffer.html#buffer_class_method_buffer_bytelength_string_encoding" rel="noreferrer"><code>Buffer.byteLength</code></a> is a method specifically for this purpose:

<pre><code>let strLengthInBytes = Buffer.byteLength(str); // str is UTF-8
</code></pre>

Note that by default the method assumes the string is in UTF-8 encoding. If a different encoding is required, pass it as the second argument.

blocks|key|1770527|text|这适用于BMP和SIP/SMP字符。|type|unstyled|depth|inlineStyleRanges|entityRanges|data|1770528|++++String.prototype.lengthInUtf8+=+function()+{
++++++++var+asciiLength+=+this.match(/[\u0000-\u007f]/g)+?+this.match(/[\u0000-\u007f]/g).length+:+0;
++++++++var+multiByteLength+=+encodeURI(this.replace(/[\u0000-\u007f]/g)).match(/%25/g)+?+encodeURI(this.replace(/[\u0000-\u007f]/g,+'')).match(/%25/g).length+:+0;
++++++++return+asciiLength+%2B+multiByteLength;
++++}

++++'test'.lengthInUtf8();
++++//+returns+4
++++'\u{2f894}'.lengthInUtf8();
++++//+returns+4
++++'سلام+علیکم'.lengthInUtf8();
++++//+returns+19,+each+Arabic/Persian+alphabet+character+takes+2+bytes.+
++++'你好，JavaScript+世界'.lengthInUtf8();
++++//+returns+26,+each+Chinese+character/punctuation+takes+3+bytes.+|code-block|syntax|javascript|1770529|entityMap^0|0|0^^$0|@$1|2|3|4|5|6|7|I|8|@]|9|@]|A|$]]|$1|B|3|C|5|D|7|J|8|@]|9|@]|A|$E|F]]|$1|G|3|-4|5|6|7|K|8|@]|9|@]|A|$]]]|H|$]]

This would work for BMP and SIP/SMP characters. 

<pre><code> String.prototype.lengthInUtf8 = function() {
 var asciiLength = this.match(/[\u0000-\u007f]/g) ? this.match(/[\u0000-\u007f]/g).length : 0;
 var multiByteLength = encodeURI(this.replace(/[\u0000-\u007f]/g)).match(/%/g) ? encodeURI(this.replace(/[\u0000-\u007f]/g, '')).match(/%/g).length : 0;
 return asciiLength + multiByteLength;
 }

 'test'.lengthInUtf8();
 // returns 4
 '\u{2f894}'.lengthInUtf8();
 // returns 4
 'سلام علیکم'.lengthInUtf8();
 // returns 19, each Arabic/Persian alphabet character takes 2 bytes. 
 '你好，JavaScript 世界'.lengthInUtf8();
 // returns 26, each Chinese character/punctuation takes 3 bytes. 
</code></pre>

blocks|key|1770467|text|您可以尝试这样做：|type|unstyled|depth|inlineStyleRanges|entityRanges|data|1770468|function+getLengthInBytes(str)+{
++var+b+=+str.match(/[%5E\x00-\xff]/g);
++return+(str.length+%2B+(!b+?+0:+b.length));+
}|code-block|syntax|javascript|1770469|这对我很管用。|1770470|entityMap^0|0|0|0^^$0|@$1|2|3|4|5|6|7|K|8|@]|9|@]|A|$]]|$1|B|3|C|5|D|7|L|8|@]|9|@]|A|$E|F]]|$1|G|3|H|5|6|7|M|8|@]|9|@]|A|$]]|$1|I|3|-4|5|6|7|N|8|@]|9|@]|A|$]]]|J|$]]

You can try this:

<pre><code>function getLengthInBytes(str) {
 var b = str.match(/[^\x00-\xff]/g);
 return (str.length + (!b ? 0: b.length)); 
}
</code></pre>

It works for me.

blocks|key|1984285|text|遇到了这个How+to+emulate+mb_strlen+in+javascript+with+strings+containing+HTML|type|unstyled|depth|inlineStyleRanges|entityRanges|offset|length|data|1984286|其中字符串与先前的答案不匹配。|1984287|我在这里得到了8的预期长度：|1984288|​|1984289|const+str+=+'X&nbsp;&#34;FUEL&#34;'
const+div+=+document.createElement("div");
div.innerHTML+=+str
console.log(div.textContent.length)|code-block|syntax|javascript|1984290|1984291|entityMap|0|LINK|mutability|MUTABLE|url|https://stackoverflow.com/questions/67057561/how-to-emulate-mb-strlen-in-javascript-with-strings-containing-html^0|5|1V|0|0|0|0|0|0|0^^$0|@$1|2|3|4|5|6|7|X|8|@]|9|@$A|Y|B|Z|1|10]]|C|$]]|$1|D|3|E|5|6|7|11|8|@]|9|@]|C|$]]|$1|F|3|G|5|6|7|12|8|@]|9|@]|C|$]]|$1|H|3|I|5|6|7|13|8|@]|9|@]|C|$]]|$1|J|3|K|5|L|7|14|8|@]|9|@]|C|$M|N]]|$1|O|3|I|5|6|7|15|8|@]|9|@]|C|$]]|$1|P|3|-4|5|6|7|16|8|@]|9|@]|C|$]]]|Q|$R|$5|S|T|U|C|$V|W]]]]

Ran into this <a href="https://stackoverflow.com/questions/67057561/how-to-emulate-mb-strlen-in-javascript-with-strings-containing-html">How to emulate mb_strlen in javascript with strings containing HTML</a>
where the string was not a good match for earlier answers.
I got the expected length of 8 here:
<div class="snippet" data-lang="js" data-hide="false" data-console="true" data-babel="false">
<div class="snippet-code">
<pre class="snippet-code-js lang-js prettyprint-override"><code>const str = 'X&amp;nbsp;&amp;#34;FUEL&amp;#34;'
const div = document.createElement("div");
div.innerHTML = str
console.log(div.textContent.length)</code></pre>
</div>
</div>

blocks|key|1770878|text|我用以下命令检查长度：|type|unstyled|depth|inlineStyleRanges|entityRanges|data|1770879|const+str+=+"as%2520"
const+len+=+new+URL(str.replace(/%25[A-F0-9]{2}/g,+"..."),+"https:$").pathname.replace(/%25[A-F0-9]{2}/g,+"-").length+-+1
console.log(len)+//+13|code-block|syntax|javascript|1770880|当我(尝试)验证目录名称是否少于180个字符时|1770881|entityMap^0|0|0|0^^$0|@$1|2|3|4|5|6|7|K|8|@]|9|@]|A|$]]|$1|B|3|C|5|D|7|L|8|@]|9|@]|A|$E|F]]|$1|G|3|H|5|6|7|M|8|@]|9|@]|A|$]]|$1|I|3|-4|5|6|7|N|8|@]|9|@]|A|$]]]|J|$]]

I'm checking the length with :
<pre class="lang-js prettyprint-override"><code>const str = &quot;as%20&quot;
const len = new URL(str.replace(/%[A-F0-9]{2}/g, &quot;...&quot;), &quot;https:$&quot;).pathname.replace(/%[A-F0-9]{2}/g, &quot;-&quot;).length - 1
console.log(len) // 13
</code></pre>
when i (try to) verify if a directory name is less than 180 characters

In my JavaScript code I need to compose a message to server in this format:

<pre><code>&lt;size in bytes&gt;CRLF
&lt;data&gt;CRLF
</code></pre>

Example:

<pre><code>3
foo
</code></pre>

The data may contain unicode characters. I need to send them as UTF-8.

I'm looking for the most cross-browser way to calculate the length of the string in bytes in JavaScript.

I've tried this to compose my payload:

<pre><code>return unescape(encodeURIComponent(str)).length + "\n" + str + "\n"
</code></pre>

But it does not give me accurate results for the older browsers (or, maybe the strings in those browsers in UTF-16?).

Any clues?

Update:

Example: length in bytes of the string <code>ЭЭХ! Naïve?</code> in UTF-8 is 15 bytes, but some browsers report 23 bytes instead.

String length in bytes in JavaScript

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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在我的JavaScript代码中，我需要编写一条发送到服务器的消息，格式如下：<size in bytes>CRLF<data>CRLF示例：3foo数据可能包含unicode字符。我需要以UTF-8格式发送它们。我正在寻找跨浏览器最多的方法来计算以字节为单位的JavaScript字符串的长度。我尝试了这个来组成我的有效负载：return unescape(encodeURIComponent(s

问字符串长度(以字节为单位)，JavaScript
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