Mongoose: Get full list of users

Well, if you really want to return a mapping from _id to user, you could always do:

server.get('/usersList', function(req, res) {
  User.find({}, function(err, users) {
    var userMap = {};

    users.forEach(function(user) {
      userMap[user._id] = user;
    });

    res.send(userMap);  
  });
});

find() returns all matching documents in an array, so your last code snipped sends that array to the client.