var bb;

var onConnect = function(connectionInfo) {
  this.connectionId = connectionInfo.connectionId;
  bb = connectionId;
}

chrome.serial.connect("COM3", {bitrate: 115200}, onConnect);


function arrayBufferToString (buffer) {
    var string = '';
    var bytes = new Uint8Array( buffer );
    var len = bytes.byteLength;
    for (var i = 0; i < len; i++) {
        string += String.fromCharCode( bytes[ i ] )
    }
    return string;
}


var stringReceived = '';

var onReceiveCallback = function(info) {
    if (info.connectionId == expectedConnectionId && info.data) {
      var str = convertArrayBufferToString(info.data);
      if (str.charAt(str.length-1) === 'n') {
        stringReceived += str.substring(0, str.length-1);
        onLineReceived(stringReceived);
        stringReceived = '';
      } else {
        stringReceived += str;
      }
    }
  };

chrome.serial.onReceive.addListener(onReceiveCallback);

var onSend = function(){
    console.log("sss");
}


var writeSerial=function(str) {
  chrome.serial.send(bb, convertStringToArrayBuffer(str), onSend);//Ошибка на эту строчку
}
var convertStringToArrayBuffer=function(str) {
  var buf=new ArrayBuffer(str.length);
  var bufView=new Uint8Array(buf);
  for (var i=0; i<str.length; i++) {
    bufView[i]=str.charCodeAt(i);
  }
  return buf;
}


var x = writeSerial();