binding method in javascript classes

Question

I have a confusing binding issue about javascript classes in node.js .

in a project, it have two type of using the classes: module1 and module2.

1. 1th module1 codes:

const controller = require('app/http/controllers/controller.js');
class homeController extends controller {
    index(req,res){
        res.send(this.message());
    }
    message(){
        return ('<p> i am home controller.js</p>');
    }
}
module.exports = new homeController();

because of, enable to use method of homeController.index, it inherits the auto-bind from controller module. if we do not use of auto-bind, when use method of homeController.index it will give error that, the message() is undefined.

so far it is ok!

but, in bellow module, it do not use of auto-bind, but the method of helpers.getObjects works correctly!

it do not gives the error that, the auth() is undefined!

2. 2th module codes:

   module.exports = class Helpers {
       constructor(req,res) {
           this.req = req;
           this.res = res;
       }
       //how works without extending the auto-bind?!
       getObjects() {
           return { auth: this.auth()};
       }
       auth() {
           return {
               check: this.req.isAuthenticated(),
               user: this.req.user
           }
       }
   }

in other word, i expect, the helpers.getObjects, only when works( it when can receive the auth() method, that it extends the auto-bind, just like modulecode(1), but it works without that!

it confused me!

what id difference?