HexString2Bytes

  HexString2Bytes(str) {
    var pos = 0;
    var len = str.length;
    if (len % 2 != 0) {
        return null;
    }
    len /= 2;
    var arrBytes = new Array();
    for (var i = 0; i < len; i++) {
        var s = str.substr(pos, 2);
        var v = parseInt(s, 16);
        arrBytes.push(v);
        pos += 2;
    }
    return arrBytes;
  }