What are these node js variables at the of the function?

Question

What are these node js variables at the of the function?

I am creating an API with NodeJS, Express and PassportJS but I think this is a JavaScript question.

app.get('/test', function (req, res, next) {
    passport.authenticate('bearer', { session: false },

    function (err, user, info) {
        if (user === false) {
            res.send('ko');
        } else {
            res.send('ok');
        }
    })(req, res, next);
});

My question is:

Why is (req, res, next) after the authenticate function? Is it related with the scope?

javascript
node.js
passport.js

Answer 1

Seems that the function password.authenticate returns a function/closure. The code is like

foo(x, y)(z);

i.e. the function returned by the call foo(x, y) is called with parameter z.

A very simple example is

function multiplier(k) {
    return function(x) { return x*k; };
}

console.log(multiplier(7)(6)); // outputs 42

Answer 2

The () call the function. The variables inside it are passed to it as arguments. You can see them coming into the containing function on line one of your code.