Utility class about UTF8 string proccessing : get utf8 string length, convert utf8 string to byte array, convert bytes array to utf8 string

UTF8.js

/**
 * Utility class about UTF8 string proccessing
 * 
 * @type UTF8
 */
var UTF8 =
{
    /**
     * Returns length in bytes of an utf8 string
     * 
     * @param {string} str
     * 
     * @returns {int}
     */
    length: function (str) {
        var m = encodeURIComponent(str).match(/%[89ABab]/g);
        return str.length + (m ? m.length : 0);
    },
    
    /**
     * Returns array of bytes of an utf8 string
     * 
     * @param {string} str
     * 
     * @returns {Uint8Array}
     */
    stringToArray: function (str) {
        var utf8 = new Uint8Array(UTF8.length(str));
        var idx = 0;
        
        for (var i=0; i < str.length; i++) {
            var charcode = str.charCodeAt(i);
            if (charcode < 0x80) utf8[idx++] = charcode;
            else if (charcode < 0x800) {
                utf8[idx++] = 0xc0 | (charcode >> 6);
                utf8[idx++] = 0x80 | (charcode & 0x3f);
            }
            else if (charcode < 0xd800 || charcode >= 0xe000) {
                utf8[idx++] = 0xe0 | (charcode >> 12); 
                utf8[idx++] = 0x80 | ((charcode>>6) & 0x3f), 
                utf8[idx++] = 0x80 | (charcode & 0x3f);
            }
            // surrogate pair
            else {
                i++;
                // UTF-16 encodes 0x10000-0x10FFFF by
                // subtracting 0x10000 and splitting the
                // 20 bits of 0x0-0xFFFFF into two halves
                charcode = 0x10000 + (((charcode & 0x3ff)<<10)
                          | (str.charCodeAt(i) & 0x3ff))
                utf8[idx++] = 0xf0 | (charcode >>18);
                utf8[idx++] = 0x80 | ((charcode>>12) & 0x3f);
                utf8[idx++] = 0x80 | ((charcode>>6) & 0x3f);
                utf8[idx++] = 0x80 | (charcode & 0x3f);
            }
        }
        
        return utf8;
    },
    
    /**
     * Decode bytes sequence to an utf8 string
     * 
     * @param {!Uint8Array} bytes
     * 
     * @returns {string}
     */
    arrayToString: function (bytes)
    {
        var encodedString = String.fromCharCode.apply(null, bytes);
        var decodedString = decodeURIComponent(escape(encodedString));
        
        return decodedString;
    }
};

/*
 * Examples:
 */
UTF8.length('¥ Jul'); // Returns 6
UTF8.stringToArray('¥ Jul'); // Returns [194, 165, 32, 74, 117, 108]
                             //          ¥         ' ' J   u    l

UTF8.arrayToString([194, 165, 32, 106, 117, 108]); // Returns '¥ jul'