如果mongo中不存在mongoClient与认证管理员连接，并创建用户

Question

每当我运行js文件时，我都会遇到以下错误     犯错^ TypeError：db.getSiblingDB不是函数

const MongoClient = require("mongodb").MongoClient;
let url = "mongodb://admin:root@localhost:27017/admin";
var client = new MongoClient(url);
client.connect(function (err, db) {
    if (err) {
        console.log("errrr", err);
    } else {
        var mongodb_user = 'user1';
        var mongodb_password = 'root';
        var mongodb_role = 'readWrite';
        var mongodb_name = 'testDb1';

        db = db.getSiblingDB(mongodb_name);
        var user = db.getUser(mongodb_user);

        if (user === null) {
            db.createUser({user: mongodb_user, pwd: mongodb_password, roles: [{role: mongodb_role, db: mongodb_name}]});
        } else {
            consoel.log("user", user);

        }

    }

});