code: function passthrough(devicename, baudrate, initialCommand=null){
      return new Promise(function(resolve, reject){
  
          // try to open the serial port
          const _device = new _serialport(devicename, {
              baudRate: parseInt(baudrate),
              autoOpen: false
          }); 
  
          // new length parser
          const parser = _device.pipe(new _lengthParser({length: 1}));
  
          // handle low-level errors
          _device.on('error', reject);
  
          // listen on incomming data
          parser.on('data', function(input){
              // passthrough
              process.stdout.write(input.toString('utf8'));
          });
  
          // open connection
          _device.open(function(err){
              if (err){
                  reject(err);
              }else{
                  // prepare
                  if (process.stdin.isTTY){
                      process.stdin.setRawMode(true);
                  }
                  
                  process.stdin.setEncoding('utf8');
  
                  // initial command set ?
                  if (initialCommand !== null){
                      _device.write(initialCommand + '\n');
                  }
  
                  // pass-through
                  process.stdin.on('data', function(data){
                      // ctrl-c ?
                      if (data == '\u0003'){
                          _device.close(function(e){
                              if (e){
                                  reject(e);
                              }else{
                                  resolve();
                              }
                          });
                      }else{
                          // passthrough stdin->serial
                          _device.write(data);
                      }
                  });
              }
          });
      });
  }
docs: serial connection to stdout;stdin