utf8 byte to unicode string

utf8ByteToUnicodeStr.js

/**
 * utf8 byte to unicode string
 * @param utf8Bytes
 * @returns {string}
 */
function utf8ByteToUnicodeStr(utf8Bytes){
    var unicodeStr ="";
    for (var pos = 0; pos < utf8Bytes.length;){
        var flag= utf8Bytes[pos];
        var unicode = 0 ;
        if ((flag >>>7) === 0 ) {
            unicodeStr+= String.fromCharCode(utf8Bytes[pos]);
            pos += 1;

        } else if ((flag &0xFC) === 0xFC ){
            unicode = (utf8Bytes[pos] & 0x3) << 30;
            unicode |= (utf8Bytes[pos+1] & 0x3F) << 24;
            unicode |= (utf8Bytes[pos+2] & 0x3F) << 18;
            unicode |= (utf8Bytes[pos+3] & 0x3F) << 12;
            unicode |= (utf8Bytes[pos+4] & 0x3F) << 6;
            unicode |= (utf8Bytes[pos+5] & 0x3F);
            unicodeStr+= String.fromCharCode(unicode) ;
            pos += 6;

        }else if ((flag &0xF8) === 0xF8 ){
            unicode = (utf8Bytes[pos] & 0x7) << 24;
            unicode |= (utf8Bytes[pos+1] & 0x3F) << 18;
            unicode |= (utf8Bytes[pos+2] & 0x3F) << 12;
            unicode |= (utf8Bytes[pos+3] & 0x3F) << 6;
            unicode |= (utf8Bytes[pos+4] & 0x3F);
            unicodeStr+= String.fromCharCode(unicode) ;
            pos += 5;

        } else if ((flag &0xF0) === 0xF0 ){
            unicode = (utf8Bytes[pos] & 0xF) << 18;
            unicode |= (utf8Bytes[pos+1] & 0x3F) << 12;
            unicode |= (utf8Bytes[pos+2] & 0x3F) << 6;
            unicode |= (utf8Bytes[pos+3] & 0x3F);
            unicodeStr+= String.fromCharCode(unicode) ;
            pos += 4;

        } else if ((flag &0xE0) === 0xE0 ){
            unicode = (utf8Bytes[pos] & 0x1F) << 12;;
            unicode |= (utf8Bytes[pos+1] & 0x3F) << 6;
            unicode |= (utf8Bytes[pos+2] & 0x3F);
            unicodeStr+= String.fromCharCode(unicode) ;
            pos += 3;

        } else if ((flag &0xC0) === 0xC0 ){ //110
            unicode = (utf8Bytes[pos] & 0x3F) << 6;
            unicode |= (utf8Bytes[pos+1] & 0x3F);
            unicodeStr+= String.fromCharCode(unicode) ;
            pos += 2;

        } else{
            unicodeStr+= String.fromCharCode(utf8Bytes[pos]);
            pos += 1;
        }
    }
    return unicodeStr;
}