How can I access a callback variable inside of another nested callback function?

Question

In the code below, Room.find().exec() has a callback function that produces the variable room . How can I access that object inside of the nested callback function inside of Player.find.exec() ?

 addplayer: function(req, res) {
    Room.find(req.param('roomid')).exec(function(err, room) {
        if (err) {
            console.log(err);
            return res.send(err, 404);
        } else {
            if (req.param('playerid') && req.param('playerid').length > 0) {
                console.log("Room found:", room);
                Player.find(req.param('playerid')).exec(function(err, player) {
                    if (err) {
                        console.log(err);
                        return res.send(err, 404);
                    } else {
                        if (typeof room.players === 'undefined' || !room.players.isArray) room.players = new Array();
                        room.players.push(player);
                        room.save();
                        console.log(player);
                        return res.send(room, 403);
                    }
                });
            } else {
                console.log('No player id.');
                return res.send('No player id.', 404);
            }
        }
    });
  }

This mighty make it easier to see what I am asking about:

Answer 1

room should still be accessible, even in a nested callback.

The reason why the variable will still be defined after the function has returned is because javascript allows the nested callback to hold references to surrounding variables.