Node.js & MongoDB API

//init
require('dotenv').config();
const express = require("express");
const app = express();
const port = process.env.PORT || 8083;
const mongoose = require("mongoose");
const bodyParser = require("body-parser");
const routes = require("./api/routes");

//Node Native Promise
mongoose.Promise = global.Promise; 

//mongodb connect
mongoose.connect(process.env.MONGO_URI).then(
    (res) => {
        console.log('Successfully connected to mongodb');
    }
).catch(e => {
    console.error(e);
});

//middleware
app.use(bodyParser.urlencoded({ extended:true }));
app.use(bodyParser.json());

//route
app.use('/', routes);

//server ready
app.listen(port, () => {
    console.log(`API server started on : ${port}`);
});

//init
const mongoose = require("mongoose");
const Schema = mongoose.Schema;

//schema
const UserSchema = new Schema({
    user_name:{
        type: String,
        required:true
    },
    user_regdate: {
        type: Date,
        default: Date.now
    }
});

module.exports = mongoose.model("User", UserSchema);

//init
const mongoose = require("mongoose");
const UserModel = mongoose.model("User");

//get users list
exports.all_users = (req, res) => {
    UserModel.find({}, (err, data) => {
        if(err) res.send(err);
        res.json(data);
    });
};

//add new user
exports.create_user = (req, res) => {
    const new_user = new UserModel(req.body);
    new_user.save((err, data) => {
        if(err) res.send(err);
        res.json(data);
    });
};

//get user
exports.load_user = (req, res) => {
    UserModel.findById(req.params.userId, (err, data) => {
        if(err) res.send(err);
        res.json(data);
    });
};

//update user
exports.update_user = (req, res) => {
    UserModel.findOneAndUpdate(
        { _id: req.params.userId },
        req.body,
        { new: true },
        (err, data) => {
            if(err) res.send(err);
            res.json(data);
        }
    );
};

//delete user
exports.delete_user = (req, res) => {
    UserModel.deleteOne(
        {
            _id: req.params.userId
        },
        (err, data) => {
            if(err) res.send(err);
            res.json({ message: "Data successfully deleted" });
        }
    );
};

//init
const express = require('express');
const router = express.Router();

//indexing routes
const user = require('./userRoutes.js');

//connect
router.use('/user', user);

//export
module.exports = router;

//init
const express = require('express');
const router = express.Router();

//activate schema
require("../models/userModel.js"); 

//controller
userController = require('../controller/userController.js');

//methods
router.route('/')
    .get(userController.all_users)
    .post(userController.create_user);

router.route('/:userId')
    .get(userController.load_user)
    .put(userController.update_user)
    .delete(userController.delete_user);

module.exports = router;