Locomotivejs is just an extension of Express, meaning a Loco app is an Express app. From the docs:
Request and Response
If an application needs access to the raw request and response, each is available as an instance variable within the controller.
PhotosController.show = function() { var req = this.req; // also aliased as this.request var res = this.res; // also aliased as this.response this.render(); }
So from within your controller, simply:
MyController.myAction = function () {
this.res.send(200);
}