Mongoose.js an ORM code example

Example 1: mongoose

import express from 'express';
or
const exporess = require('express');
import mongoose from 'mongoose';
or
const mongoose = require('mongoose');
const app = express();
mongoose.connect('mongodb://localhost:27017/mongo-tree' , {
    useNewUrlParser: true,
    useUnifiedTopology: true
});

const db = mongoose.connection;
db.on('error', console.error.bind(console, 'connection error:'));
db.once('open', function() {
console.log('connected db')
});
app.use('/', (req, res) => {
    res.send('hello');
}
);
const port = process.env.PORT || 5000
app.listen(port, () => {
console.log('running');
})
//for es6 >npm i @babel/core @babel/node @babel/preset-env --save-dev

//create  .babelrc file and put this 
{
    "presets": [
        "@babel/preset-env"
    ]
}
//and package.json
  "scripts": {
    "test": "echo \"Error: no test specified\" && exit 1",
    "start": "nodemon --exec babel-node server"
  },

Example 2: mongoose node js

var db = mongoose.connection;
db.on('error', console.error.bind(console, 'connection error:'));
db.once('open', function() {
  // we're connected!
});