Node.js: crypto.pbkdf2 hex password

I am currently using the following setting to register new users:

// creates a new user
app.post('/users', function(req, res) {
    // create new user
    var user = new User();
    // assign post
    user.username = req.body.username;
    user.email = req.body.email;

    crypto.randomBytes(32, function(err, buf) {
        if (err) throw err;
        user.salt = buf.toString('hex');
        crypto.pbkdf2(req.body.password, user.salt, 25000, 512, function(err, encodedPassword) {
            if (err) throw err;
            user.password = (encodedPassword.toString('hex')); // this line
            user.save(function(err, user) {
                if (!err) return res.send(err, 500);
                return res.json(user);
            });
        }.bind(this));
    });
});

Take a close look at this line:

user.password = (encodedPassword.toString('hex'));

This should encode the password string (which looks like binary) into a hexadecimal string. For some reason this does not work.

Why not?

Byside : What encoding is the recommendation for storing salt and password (hex, binary, base64)?