Node.js - Create strong password hashes with this function

Hashing your user passwords before committing them to persistent storage is a must in any environment where security is important. Node.js makes this easy to do with its built-in crypto library. Here's a node.js function I use to generate strong password hashes using node.js' crypto.pbkdf2 functionality:

// generate a strong password hash (make sure you choose a salt
// or capture the salt randomly generated for you!)
var hashPassword = function (opts, callback) {
    // make sure some plaintext is present 
    // if not make some up and call this method recursively
    if (!opts.plaintext) {
        return crypto.randomBytes(6, function (err, buf) {
            if (err) callback(err);
            opts.plaintext = buf.toString('base64');
            return hashPassword(opts, callback);
        })
    }
    // make sure a salt is present in input
    // if not make a salt up
    if (!opts.salt) {
        return crypto.randomBytes(64, function (err, buf) {
            if (err) return callback(err);
            opts.salt = buf;
            return hashPassword(opts, callback);
        })
    }
    // we use pbkdf2 to hash and iterate 10k times by default 
    // hashed password is in opts.key in the callback
    opts.hash = 'sha1';
    opts.iterations = opts.iterations || 10000;
    return crypto.pbkdf2(opts.plaintext, opts.salt, opts.iterations, 64, function (err, key) {
        if (err) return callback(err);
        opts.key = new Buffer(key);
        return callback(null, opts);
    })
};