Communicating with multiple Espruino devices

We are currently using the below code with no success. The slaves are connected through a USB connector so do we need a 4.7k pull-up resistor on each slave or just once? (Currently we have one)

//Master
E.setBootCode("function cmdOnSlave(slave, cmd) {
     Serial1.println('if(ID==\"' + slave + '\")' + cmd + ';');
}
USB.setConsole(true); // make sure console stays off Serial1
var line = '';
Serial1.on('data', function(d) {
     line += d;
     i = line.indexOf('\n');
     while (i >= 0) {
          console.log(line.substr(0, i)); // do stuff with data
          line = line.substr(i + 1);
          i = line.indexOf('\n');
    }
});
", true)

//Slave
E.setBootCode("
    var ID = getSerial();
    pinMode(B6, 'af_opendrain');
     echo(0);
", true);