llagerlof
11/11/2011 - 3:56 PM

Function to count bytes of a string (UTF8)

Function to count bytes of a string (UTF8)

index.html
content_copyfile_download
<html>
<head>
    <title>String size with countUtf8</title>
    <script type="text/javascript" src="count_utf8.js"></script>
</head>
<body>
    <script type="text/javascript">
        document.write( "The string size in bytes is " + countUtf8("a€bð¤­Â¢") );
    </script>
</body>
</html>
count_utf8.js
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/**
 * Function to fix native charCodeAt()
 *
 * Now, we can use fixedCharCodeAt("foo€", 3); for multibyte (non-bmp) chars too.
 *
 * @access public
 * @see https://developer.mozilla.org/en/JavaScript/Reference/Global_Objects/String/charCodeAt
 * @note If you hit a non-bmp surrogate, the function will return false
 * @param str String Mixed string to get charcodes
 * @param idx Integer Position of the char to get
 * @return code Integer Result charCodeAt();
 */
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;
}

/**
 * Gets size of a UTF-8 string in bytes
 *
 * @autor Frank Neff <fneff89@gmail.com>
 * @license GPL v2
 * @access public
 * @param str String Input string to get bytesize
 * @return result String Size of the input string in 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;
}