Where does the var User come from in Passport documentation

Question

Where does the var User come from in Passport documentation

I am just getting my head round Passport in Node

 passport.use(new LocalStrategy(
   function(username, password, done) {
     User.findOne({ username: username }, function (err, user) {
       if (err) { return done(err); }
       if (!user) {
         return done(null, false, { message: 'Incorrect username.' });
       }
       if (!user.validPassword(password)) {
         return done(null, false, { message: 'Incorrect password.' });
       }
       return done(null, user);
     });
   }
 ));

This is all great, I understand the logic. However I don't understand where variables User from

User.findOne({ username:....

Is coming from? This isn't set anywhere and baffles me a little.

javascript
node.js
passport.js

Answer 1

The example is using a mongoose model (User) that was defined elsewhere. Mongoose models have a findOne function. It's meant to mostly be filler to show how you would use the strategy to lookup info in the db to authenticate the user.