[рони]

SE-Den,

function MDB(callback)  {
    const mongoose = require("mongoose");
    const Schema = mongoose.Schema;

    // установка схемы
    const userScheme = new Schema({
        name: String,
        age: Number
    });

    // подключение
    mongoose.connect("mongodb://localhost:27017/usersdb", { useUnifiedTopology: true });

    const User = mongoose.model("User", userScheme);
    const user = new User({
        name: "Bill",
        age: 41
    });

    User.findOne({name: "Bill"}, function(err, doc){
        mongoose.disconnect();
        if(err) return console.log(err);
        if(callback) callback(doc.name);
    });
}

const callback = res => console.log(res);
MDB(callback);