express callback next callback (also how to protect a link for example /profile)

express_callback_next_calback.js

// in express we can pass a callback to another callback using next
// for example if we need to choose between two response (if condition is made res.send else res.send) to do that we need to pass next() 
// callback to else in our middleware

// in the auth_middleware.js
let authenticated = false;
let requireLogin = (req, res, next) => {
    if (!authenticated) {
        res.send('not logged in'); // res.redirect('/login');
        console.log('not logged');
    } else {
        next();
        console.log('you are logged');
    }
}

// in the router
let auth = require('../../auth_middleware.js');
router.get('/profile', auth.userLogged, (req, res) => {
    res.send('helloooooo to your profile'); //or res.render('dashboard.pug');
})