mongodb pooling

app.js

const express = require('express');
const app = express();
const db = require('./database.js');

app.listen(3000);
console.log("Listening on port 3000");

app.get("/", (req, res) =>{
    db.query().then(docs =>{
        res.send(docs);
    });
});

database.js

const mongodb = require('mongodb');
let db;
init();

function init() {
    const url = 'mongodb://127.0.0.1:27017/test';
    mongodb.MongoClient.connect(url).then((initialized) => {
        db = initialized;
    });
}


exports.query = function () {
    let p = db.collection('restaurants').find({}).toArray();
    return p;
};

shell.js

> use test
switched to db test
> db.restaurants.insert(                                     
...    {                                                     
...       "address" : {                                      
...          "street" : "2 Avenue",                          
...          "zipcode" : "10075",                            
...          "building" : "1480",                            
...          "coord" : [ -73.9557413, 40.7720266 ]           
...       },                                                 
...       "borough" : "Manhattan",                           
...       "cuisine" : "Italian",                             
...       "grades" : [                                       
...          {                                               
...             "date" : ISODate("2014-10-01T00:00:00Z"),    
...             "grade" : "A",                               
...             "score" : 11                                 
...          },                                              
...          {                                               
...             "date" : ISODate("2014-01-16T00:00:00Z"),    
...             "grade" : "B",                               
...             "score" : 17                                 
...          }                                               
...       ],                                                 
...       "name" : "Vella",                                  
...       "restaurant_id" : "41704620"                       
...    }                                                     
... )                                                        
WriteResult({ "nInserted" : 1 })
> db.restaurants.find().toArray()