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This is my first attempt at developing with a chrome app or extension. I have a GPS receiver on the USB port which is emulated as a serial device.

Running this code

var onGetDevices = function(ports) {

for (var i=0; i<ports.length; i++) {

    // show me some output
    console.log(ports[i].path);

    // Connect to the serial port /dev/ttyUSB0
    chrome.serial.connect(ports[i].path, {bitrate: 9600}, onConnect);   
  }
}
chrome.serial.getDevices(onGetDevices);

gets me "/dev/ttyUSB0" in the console, so it appears to be finding the device.

How do I then connect to the device? I've included the serial.connect line above, with the following functions:

var onConnect = function(connectionInfo) {
    // The serial port has been opened. Save its id to use later.
    _this.connectionId = connectionInfo.connectionId;

    // Do whatever you need to do with the opened port.
    chrome.serial.onReceive.addListener(onReceiveCallback);
}

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;
      }
  }
};

but I get the following error:

Error in response to serial.connect: ReferenceError: _this is not defined at Object.onGetDevices [as callback]

I'm not sure exactly what I'm doing right or wrong here so any pointers appreciated.

This is my first attempt at developing with a chrome app or extension. I have a GPS receiver on the USB port which is emulated as a serial device.

Running this code

var onGetDevices = function(ports) {

for (var i=0; i<ports.length; i++) {

    // show me some output
    console.log(ports[i].path);

    // Connect to the serial port /dev/ttyUSB0
    chrome.serial.connect(ports[i].path, {bitrate: 9600}, onConnect);   
  }
}
chrome.serial.getDevices(onGetDevices);

gets me "/dev/ttyUSB0" in the console, so it appears to be finding the device.

How do I then connect to the device? I've included the serial.connect line above, with the following functions:

var onConnect = function(connectionInfo) {
    // The serial port has been opened. Save its id to use later.
    _this.connectionId = connectionInfo.connectionId;

    // Do whatever you need to do with the opened port.
    chrome.serial.onReceive.addListener(onReceiveCallback);
}

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;
      }
  }
};

but I get the following error:

Error in response to serial.connect: ReferenceError: _this is not defined at Object.onGetDevices [as callback]

I'm not sure exactly what I'm doing right or wrong here so any pointers appreciated.

• javascript
• google-chrome
• serial-port
• google-chrome-app

Share Improve this question Follow edited Jul 28, 2014 at 16:28 Xan 77.6k1818 gold badges197197 silver badges217217 bronze badges asked Jul 27, 2014 at 21:55 user2672288user2672288 3

• It looks like the variable _this isn't defined in your code. – Derek 朕會功夫 Commented Jul 28, 2014 at 9:46
• the code was taken directly from chromes tutorial example though, does it need defining, if so what as? link here developer.chrome./apps/app_serial – user2672288 Commented Jul 28, 2014 at 9:49
• this is great, good question – Shassain Commented Jun 24, 2018 at 0:21

Add a ment  | 

1 Answer 1

Sorted by: Reset to default 4

First the example does not work properly. Try this instead:

var connectionId;

$(document).ready(function() {
    chrome.serial.getDevices(function(devices) {

        for (var i = 0; i < devices.length; i++) {
            $('select#portList').append('<option value="' + devices[i].path + '">' + devices[i].path + '</option>');
        }
    });

    // ui hook
    $('button#open').click(function() {
        var clicks = $(this).data('clicks');

        if (!clicks) {
            var port = $('select#portList').val();
            chrome.serial.connect(port, {bitrate: 9600}, function(info) {
                connectionId = info.connectionId;
                $("button#open").html("Close Port");
                console.log('Connection opened with id: ' + connectionId + ', Bitrate: ' + info.bitrate);
            });
        } else {
            chrome.serial.disconnect(connectionId, function(result) {
                $("button#open").html("Open Port");
                console.log('Connection with id: ' + connectionId + ' closed');
            });
        }

        $(this).data("clicks", !clicks);
    });
});

Now as for the actual reading of the input from the serial connection it will work but converting the ArrayBuffer to a string is a bit harder than expected.

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