Count bytes in textarea using javascript

Question

I need to count how long in bytes a textarea is when UTF8 encoded using javascript. Any idea how I would do this?

thanks!

Answer 1

[June 2020: The previous answer has been replaced due to it returning incorrect results].

Most modern JS environments (browsers and Node) now support the TextEncoder API, which may be used as follows to count UTF8 bytes:

const textEncoder = new TextEncoder();
textEncoder.encode('⤀⦀⨀').length; // => 9

This is not quite as fast as the getUTF8Length() function mentioned in other answers, below, but should suffice for all but the most demanding use cases. Moreover, it has the benefit of leveraging a standard API that is well-tested, well-maintained, and portable.

Answer 2

How about simple:

unescape(encodeURIComponent(utf8text)).length

The trick is that encodeURIComponent seems to work on characters while unescape works on bytes.

Answer 3

I have been asking myself the same thing. This is the best answer I have stumble upon:

http://www.inter-locale.com/demos/countBytes.html

Here is the code snippet:

<script type="text/javascript">
 function checkLength() {
    var countMe = document.getElementById("someText").value
    var escapedStr = encodeURI(countMe)
    if (escapedStr.indexOf("%") != -1) {
        var count = escapedStr.split("%").length - 1
        if (count == 0) count++  //perverse case; can't happen with real UTF-8
        var tmp = escapedStr.length - (count * 3)
        count = count + tmp
    } else {
        count = escapedStr.length
    }
    alert(escapedStr + ": size is " + count)
 }

but the link contains a live example of it to play with. "encodeURI(STRING)" is the building block here, but also look at encodeURIComponent(STRING) (as already point out on the previous answer) to see which one fits your needs.

Regards

Answer 4

If you have non-bmp characters in your string, it's a little more complicated...

Because javascript does UTF-16 encode, and a "character" is a 2-byte-stack (16 bit) all multibyte characters (3 and more bytes) will not work:

    <script type="text/javascript">
        var nonBmpString = "foo€";
        console.log( nonBmpString.length );
        // will output 5
    </script>

The character "€" has a length of 3 bytes (24bit). Javascript does interpret it as 2 characters, because in JS, a character is a 16 bit block.

So to correctly get the bytesize of a mixed string, we have to code our own function fixedCharCodeAt();

    function fixedCharCodeAt(str, idx) {
        idx = idx || 0;
        var code = str.charCodeAt(idx);
        var hi, low;
        if (0xD800 <= code && code <= 0xDBFF) { // High surrogate (could change last hex to 0xDB7F to treat high private surrogates as single characters)
            hi = code;
            low = str.charCodeAt(idx + 1);
            if (isNaN(low)) {
                throw 'Kein gültiges Schriftzeichen oder Speicherfehler!';
            }
            return ((hi - 0xD800) * 0x400) + (low - 0xDC00) + 0x10000;
        }
        if (0xDC00 <= code && code <= 0xDFFF) { // Low surrogate
            // We return false to allow loops to skip this iteration since should have already handled high surrogate above in the previous iteration
            return false;
            /*hi = str.charCodeAt(idx-1);
            low = code;
            return ((hi - 0xD800) * 0x400) + (low - 0xDC00) + 0x10000;*/
        }
        return code;
    }

Now we can count the bytes...

    function countUtf8(str) {
        var result = 0;
        for (var n = 0; n < str.length; n++) {
            var charCode = fixedCharCodeAt(str, n);
            if (typeof charCode === "number") {
                if (charCode < 128) {
                    result = result + 1;
                } else if (charCode < 2048) {
                    result = result + 2;
                } else if (charCode < 65536) {
                    result = result + 3;
                } else if (charCode < 2097152) {
                    result = result + 4;
                } else if (charCode < 67108864) {
                    result = result + 5;
                } else {
                    result = result + 6;
                }
            }
        }
        return result;
    }

By the way... You should not use the encodeURI-method, because, it's a native browser function ;)

More stuff:

• Code on GitHub
• More on Mozilla Developer Networks

---

Cheers

frankneff.ch / @frank_neff

Answer 5

Add Byte length counting function to the string

String.prototype.Blength = function() {
    var arr = this.match(/[^\x00-\xff]/ig);
    return  arr == null ? this.length : this.length + arr.length;
}

then you can use .Blength() to get the size

Answer 6

Try the following:

function b(c) {
     var n=0;
     for (i=0;i<c.length;i++) {
           p = c.charCodeAt(i);
           if (p<128) {
                 n++;
           } else if (p<2048) {
                 n+=2;
           } else {
                 n+=3;
           }
      }return n;
}