Interfacing to Adafruit fingerprint sensor

And here is the code I have so far.
Please note it was late, not necessarly optimized and the way the onData is done might change later :)
Also I will add an 'err' as first parameter for each callback in case,
and adapt some part of code.
Once Enroll is done, I will start transforming and prepare for module

var C = {
  FINGERPRINT_OK                 : 0x00,
  FINGERPRINT_PACKETRECIEVEERR   : 0x01,
  FINGERPRINT_NOFINGER           : 0x02,
  FINGERPRINT_IMAGEFAIL          : 0x03,
  FINGERPRINT_IMAGEMESS          : 0x06,
  FINGERPRINT_FEATUREFAIL        : 0x07,
  FINGERPRINT_NOMATCH            : 0x08,
  FINGERPRINT_NOTFOUND           : 0x09,
  FINGERPRINT_ENROLLMISMATCH     : 0x0A,
  FINGERPRINT_BADLOCATION        : 0x0B,
  FINGERPRINT_DBRANGEFAIL        : 0x0C,
  FINGERPRINT_UPLOADFEATUREFAIL  : 0x0D,
  FINGERPRINT_PACKETRESPONSEFAIL : 0x0E,
  FINGERPRINT_UPLOADFAIL         : 0x0F,
  FINGERPRINT_DELETEFAIL         : 0x10,
  FINGERPRINT_DBCLEARFAIL        : 0x11,
  FINGERPRINT_PASSFAIL           : 0x13,
  FINGERPRINT_INVALIDIMAGE       : 0x15,
  FINGERPRINT_FLASHERR           : 0x18,
  FINGERPRINT_INVALIDREG         : 0x1A,
  FINGERPRINT_ADDRCODE           : 0x20,
  FINGERPRINT_PASSVERIFY         : 0x21,

  FINGERPRINT_STARTCODE          : 0xEF01,

  FINGERPRINT_COMMANDPACKET      : 0x1,
  FINGERPRINT_DATAPACKET         : 0x2,
  FINGERPRINT_ACKPACKET          : 0x7,
  FINGERPRINT_ENDDATAPACKET      : 0x8,

  FINGERPRINT_TIMEOUT            : 0xFF,
  FINGERPRINT_BADPACKET          : 0xFE,

  FINGERPRINT_GETIMAGE           : 0x01,
  FINGERPRINT_IMAGE2TZ           : 0x02,
  FINGERPRINT_REGMODEL           : 0x05,
  FINGERPRINT_STORE              : 0x06,
  FINGERPRINT_EMPTY              : 0x0D,
  FINGERPRINT_VERIFYPASSWORD     : 0x13,
  FINGERPRINT_HISPEEDSEARCH      : 0x1B,
  FINGERPRINT_TEMPLATECOUNT      : 0x1D,

  DEFAULTTIMEOUT : 5000 // milliseconds
};

Serial4.setup(57600);

var thePassword = 0;
var theAddress = 0xFFFFFFFF;

function writePacket(addr, packetType, packet) {
  var len = packet.length+2;
  Serial4.write([
    (C.FINGERPRINT_STARTCODE >> 8) & 0xFF,
    C.FINGERPRINT_STARTCODE & 0xFF,
    (addr >> 24) & 0xFF,
    (addr >> 16) & 0xFF,
    (addr >> 8) & 0xFF,
    addr & 0xFF,
    packetType,
    (len >> 8) & 0xFF,
    len &0xFF
  ]);

  var sum = (len>>8) + (len&0xFF) + packetType;
  Serial4.write(packet);
  for (var i in packet) sum += packet[i];
  Serial4.write([(sum>>8)&0xFF, sum&0xFF]);
}

function getReply(packet, callback) {

  var receivedData = [];// new Uint8Array(20);

  Serial4.onData(function (e) {
    receivedData.push(e.data.charCodeAt(0));

    if ( (idx === 0) && (receivedData[0] != ( (C.FINGERPRINT_STARTCODE >> 8) & 0xFF) ))
      return;

    if (receivedData.length >= 9) {

      if (( receivedData[0] != (C.FINGERPRINT_STARTCODE >> 8)) ||
          ( receivedData[1] != (C.FINGERPRINT_STARTCODE & 0xFF)))
        console.log('bad packet');

      var packettype = receivedData[6];
      var len = receivedData[7];

      len = len << 8 & 0xFF;
      len = len | (receivedData[8] & 0xFF);
      len -= 2;

      if (receivedData.length <= (len+10))
        return;

      packet[0] = packettype;

      for (var i=0; i<len; i++) {
        packet[1+i] = receivedData[9+i];
      }

      console.log('end');  
      callback(len, packet);
    }
  });
}

function verifyPassword(callback) {
  var packet = [
    C.FINGERPRINT_VERIFYPASSWORD,
    (thePassword >> 24) & 0xFF,
    (thePassword >> 16) & 0xFF,
    (thePassword >> 8) & 0xFF,
    thePassword & 0xFF
  ];

  writePacket(theAddress, C.FINGERPRINT_COMMANDPACKET, packet);

  getReply(packet, function(len, packet) {
    if ((len == 1) && (packet[0] == C.FINGERPRINT_ACKPACKET) && (packet[1] == C.FINGERPRINT_OK))
      callback(true);
    else
      callback(false);
  });
}

function getImage(callback) {
  var packet = [C.FINGERPRINT_GETIMAGE];

  writePacket(theAddress, C.FINGERPRINT_COMMANDPACKET, packet);

  getReply(packet, function(len, packet) {
    if ((len != 1) && (packet[0] != C.FINGERPRINT_ACKPACKET))
      callback(-1);
    else
      callback(packet[1]);
  });
}

function image2Tz(slot, callback) {
  var packet = [C.FINGERPRINT_IMAGE2TZ, (slot & 0xFF)];

  writePacket(theAddress, C.FINGERPRINT_COMMANDPACKET, packet);

  getReply(packet, function(len, packet) {
    if ((len != 1) && (packet[0] != C.FINGERPRINT_ACKPACKET))
      callback(-1);
    else
      callback(packet[1]);
  });
}

function fingerFastSearch(callback) {
  var fingerID = 0xFFFF;
  var confidence = 0xFFFF;
  var packet = [C.FINGERPRINT_HISPEEDSEARCH, 0x01, 0x00, 0x00, 0x00, 0xA3];

  writePacket(theAddress, C.FINGERPRINT_COMMANDPACKET, packet);

  getReply(packet, function(len, packet) {

    if ((len != 1) && (packet[0] != C.FINGERPRINT_ACKPACKET)) {
      callback(-1);
      return;
    }

    fingerID = packet[2];
    fingerID <<= 8;
    fingerID |= packet[3];

    confidence = packet[4];
    confidence <<= 8;
    confidence |= packet[5];

    callback(packet[1], fingerID, confidence);
  });
}

function getFingerprintIDez(callback) {
  getImage(function(f) {
    if (f != C.FINGERPRINT_OK) {
      callback(-1);
      return;
    }
    image2Tz(null, function(g) {
      if (g != C.FINGERPRINT_OK) {
        callback(-1);
        return;
      }
      fingerFastSearch(function(res, fingerID, confidence) {
        if (res != C.FINGERPRINT_OK) {
          callback(-1);
          return;
        }

        callback(fingerID);

      });
    });
  });
}


//setup
verifyPassword(function(e) {
  if(e) {
    getFingerprintIDez(function(e) {
      console.log(e);
    });
  }
});