Generate Random unique key(hash) - Javascript + Node.Js [on hold]

My api code:

exports.signUp = function (req, res) {
    var newadmin = {
        username: req.body.username,
        firstname: req.body.firstname,
        userKey: // i need random unique key here
        password: encrypt(req.body.password)
    }
    Admin.create(newadmin).then(function (user) {
        return res.status(200).send(user);
    });
}

In my api i have userKey: column in this i want to insert some random unique key.