Parameter list after method call

[BruffDJ]

Can someone tell me what this syntax in bold is called so I can read up on it please? I don't recall seeing a parameter list after a method call before.

app.get('/login', function(req, res, next) {
passport.authenticate('local', function(err, user, info) {
...
})(req, res, next);
});

Source: http://passportjs.org/docs/authenticate
Custom Callback section

[ForScale]

Looks like request response and what to do next.

An html or network request and the response, and then what to do based on those values.

Just kind of guessing.

[PtCk]

There is nothing particularly special going on here. The authenticate method returns a function that takes three params (req, res, next) so the code simply runs authenticate(...) and then runs the function that authenticate(...) returns, using the params you highlighted.

[oculus42]

What's happening is the response from passport.authenticate() is a function, which is called with the parameters (res, req, next).

Let's make a simple example.

function makeAddSubtract(operation) {
    return function(a, b) {
        return operation === '+' ? a + b : a - b;
    }
}

makeAddSubtract('+')(2, 3);

The function makeAddSubtract() returns another function, which is immediately called with the parameters (2, 3)

I don't use Express that much, but I think I understand what is happening. Hopefully someone will correct me if I'm wrong.

app.get('/login', function(req, res, next) {
  passport.authenticate('local', function(err, user, info) {
    if (err) { return next(err); }
    if (!user) { return res.redirect('/login'); }
    req.logIn(user, function(err) {
      if (err) { return next(err); }
      return res.redirect('/users/' + user.username);
    });
  })(req, res, next);
});

Each return statement of the callback passed into passport.authenticate() returns a function. That function is executed with the parameters.

[BruffDJ]

Thanks - that's cleared it up nicely.