node.js wait for events on variable length array type

Question

so I am writing a small application which exposes the serial port to a web service.

The client is allowed to open ports and the server keeps track on what ports are opened.

I am a complete newbie to javascript so please also point out any other errors you can see in my code!

anyway I have websockets to pass messaged between the client and the server.

There is a ser_con event which instructs the server to open a new connection to a serial port. This also appends serialport object to an array so I can later refer to it.

var ser = []
...
socket.on('ser_con', function(d) {
  console.log('connect event')
  sp = new SerialPort.SerialPort(d.name, {
    baudrate: d.baudrate,
    databits: d.databits,
    stopbits: d.stopbits,
    parity: d.parity,
    buffersize: d.buffersize,
    parser: SerialPort.parsers.raw
  },false);
  sp.open(function (err) {
    if (err) {
      console.log('Error connecting to port: ' + d.name + ', error: ' + err);
      socket.emit('ser_err', 'Error connecting to port: ' + d.name + ', error: ' + err);
    } else {
      console.log('connected to serial port ' + d.name);
      data = {
        name: d.name,
        b:'connected to serial port ' + d.name + '\n'
      }
      socket.emit('data', data);
      ser.push({'name':d.name,'sp':sp})
    }
  })
});

So once connection is succesfull I append the name of the port and the instance of the serialport object to the ser array.

The problem I am having is on how I can listen to events on all the serialports instances

I tried doing this but it doesn't work, I assume this isn't allowed since the for loop isn't an event by itself. I have no idea how to solve this though since...

for (var i=0; i < ser.length; i++){
  ser[i].sp.on('data', function(d) {
    console.log('recieved data on port ' + ser[i].name)
    data = {
      name: ser[i].name,
      b: d
    }
    socket.emit('data', data);
  });
}

any help is appreciated.

score 0 · Accepted Answer · edited May 23 '17 at 11:58

You are using for iterator variable in the callbacks. This is a common javascript mistake. To fix this:

for (var j=0; j < ser.length; j++){
  (function(i){
    ser[i].sp.on('data', function(d) {
        console.log('recieved data on port ' + ser[i].name)
        data = {
          name: ser[i].name,
          b: d
        }
        socket.emit('data', data);
      });
  }(j))  
}

I don't know where in your code you are running this for loop. But if you are not properly handling this you might end up binding multiple callbacks to the same serial port object. I recommend to bind events after opening the port:

...
sp.open(function (err) {
    if (err) {
      console.log('Error connecting to port: ' + d.name + ', error: ' + err);
      socket.emit('ser_err', 'Error connecting to port: ' + d.name + ', error: ' + err);
    } else {
      console.log('connected to serial port ' + d.name);
      data = {
        name: d.name,
        b:'connected to serial port ' + d.name + '\n'
      }
      socket.emit('data', data);
      ser.push({'name':d.name,'sp':sp})

      //listen 'data' event here
      //you have access to both 'd' and 'socket' variable here
      sp.on('data', function(data) {
        console.log('recieved data on port ' + d.name)
        data = {
          name: d.name,
          b: data
        }
        socket.emit('data', data);
      });
    }
})

thank you! I didn't think to install event handler into a local variable. — , Jun 29 '15 at 17:17

node.js wait for events on variable length array type

1 Answers1