Encode/Decode UTF8 with javascript. more at: https://gist.github.com/avenauche/4585741

URIcomponent.js

// http://kenany.me/blog/base64-js/
var utf8 = {
    encode: function(str) { return unescape( encodeURIComponent(str) ); },
    decode: function(str) { return decodeURIComponent( escape(str) ); }
};

UTF8.encode_decode.js

/* - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - -  */
/*  Utf8 class: encode / decode between multi-byte Unicode characters and UTF-8 multiple          */
/*              single-byte character encoding (c) Chris Veness 2002-2011                         */
/* - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - -  */

/* changelog 
 * 2013-02-14: changed namespace to object literal
 * 2010-09-29: fixed decode order of operation to avoid falsely recognising decoded string as 3-byte 
 *             utf-8 charaacter
 */

var UTF8 = {

    /**
     * Encode multi-byte Unicode string into utf-8 multiple single-byte characters
     * (BMP / basic multilingual plane only)
     *
     * Chars in range U+0080 - U+07FF are encoded in 2 chars, U+0800 - U+FFFF in 3 chars
     *
     * @param {String} strUni Unicode string to be encoded as UTF-8
     * @returns {String} encoded string
     */
    encode: function (strUni) {
        // use regular expressions & String.replace callback function for better efficiency
        // than procedural approaches
        var strUtf = strUni.replace(
            /[\u0080-\u07ff]/g, // U+0080 - U+07FF => 2 bytes 110yyyyy, 10zzzzzz
        function (c) {
            var cc = c.charCodeAt(0);
            return String.fromCharCode(0xc0 | cc >> 6, 0x80 | cc & 0x3f);
        });
        strUtf = strUtf.replace(
            /[\u0800-\uffff]/g, // U+0800 - U+FFFF => 3 bytes 1110xxxx, 10yyyyyy, 10zzzzzz
        function (c) {
            var cc = c.charCodeAt(0);
            return String.fromCharCode(0xe0 | cc >> 12, 0x80 | cc >> 6 & 0x3F, 0x80 | cc & 0x3f);
        });
        return strUtf;
    },

    /**
     * Decode utf-8 encoded string back into multi-byte Unicode characters
     *
     * @param {String} strUtf UTF-8 string to be decoded back to Unicode
     * @returns {String} decoded string
     */
    decode: function (strUtf) {
        // note: decode 3-byte chars first as decoded 2-byte strings could appear to be 3-byte char!
        var strUni = strUtf.replace(
            /[\u00e0-\u00ef][\u0080-\u00bf][\u0080-\u00bf]/g, // 3-byte chars
        function (c) { // (note parentheses for precence)
            var cc = ((c.charCodeAt(0) & 0x0f) << 12) | ((c.charCodeAt(1) & 0x3f) << 6) | (c.charCodeAt(2) & 0x3f);
            return String.fromCharCode(cc);
        });
        strUni = strUni.replace(
            /[\u00c0-\u00df][\u0080-\u00bf]/g, // 2-byte chars
        function (c) { // (note parentheses for precence)
            var cc = (c.charCodeAt(0) & 0x1f) << 6 | c.charCodeAt(1) & 0x3f;
            return String.fromCharCode(cc);
        });
        return strUni;
    }
};