How can I make a flat trim for an AR.Drone 2.0 using node-ar-drone?

I am using node-ar-drone to control a drone, and before taking off I would like to perform a flat trim. However, I have notice that there is no a function in this module for doing this, so I wonder how I can do it.

node-ar-drone has an ftrim function that performs a flat trim:

var arDrone = require('ar-drone');
var client  = arDrone.createClient();
// Flat trim.
client.ftrim();