code: function checkConnection(){
  
      return new Promise(function(resolve, reject){
  
          // 1.5s connection timeout
          const watchdog = setTimeout(function(){
              // throw error
              reject(new Error('Timeout, no response detected - is NodeMCU online and the Lua interpreter ready ?'));
          }, 1500);
  
          // send a simple print command to the lua engine
          _virtualTerminal.executeCommand(_luaCommandBuilder.command.echo)
              .then(({echo, response}) => {
                  // clear watchdog
                  clearTimeout(watchdog);
  
                  // validate command echo and command output
                  if (response == 'echo1337' && echo == 'print("echo1337")') {
                      resolve();
                  } else {
                      _logger.log('Echo:', echo);
                      _logger.debug('Response:', response);
                      reject(new Error('No response detected - is NodeMCU online and the Lua interpreter ready ?'));
                  }
              })
              .catch(reject)
      });
  
  }
docs: checks the node-mcu connection