code: function handleConnectionCallback(err, resolve, reject, key, connection) {
    debug('handleConnectionCallback','start');
  
    //error, remove cached entry, reject the promise
    if (err) {
      debug('handleConnectionCallback','error',err);
      delete promises[key];
      return reject(err);
    }
  
    //patch close method for caching
    shadowClose(connection);
  
    //create a reference to the original connection for cleanup
    connection._mssqlngKey = key;
  
    //add connection to the pool
    connections[connection._mssqlngKey] = connection;
  
    //resolve the promise
    debug('handleConnectionCallback','success');
    return resolve(connection);
  }
docs: handle promise resolution for connection callback