DRY?

route.js

exports.whater = function (req, res) {
    var format = req.params.format ? req.params.format : req.format;

    User.findOne({ username: req.params.username }, function (err, doc) {
        if (err) throw err;
        if (!doc) {
            if (format == 'json') {
                res.json({ error: "no such user"});
            } else {
                res.render('404');
            }
        } else {
            if (format == 'json') {
                res.json(doc);
            } else {
                res.render('user/show', { user: doc });
            }
        }
    });
};