javascript - how to connect mongoDB to server? -

i trying data mongodb while connecting server .i inserted 1 value in mongodb this

> use abc   switched db abc > db.ac.insert({name:"naveen"}) writeresult({ "ninserted" : 1 }) > show collections ac system.indexes  

and try value this

var express=require('express'); var app =express(); var mongoclient = require('mongodb').mongoclient; var assert = require('assert');   app.get('/',function(req,res){     console.log("connected  server.");      mongoclient.connect(url, function(err, db) {         assert.equal(null, err);         var collection = db.collection('ac');         console.log(collection)         console.log("connected correctly server.");         db.close();     }); })  var url = 'mongodb://localhost:27017/abc';   app.listen(3000,function(){          console.log('server runninngn') }) 

i getting error why ?

macbook-pro:expressjs naveenkumar$ node index.js server runninngn connected  server. { s:     { pkfactory:        { [function: objectid]         index: 462263,         createpk: [function: createpk],         createfromtime: [function: createfromtime],         createfromhexstring: [function: createfromhexstring],         isvalid: [function: isvalid],         objectid: [circular],         objectid: [circular] },      db:        { domain: null,         _events: {},         _maxlisteners: 10,         s: [object],         serverconfig: [getter],         buffermaxentries: [getter],         databasename: [getter],         options: [getter],         native_parser: [getter],         slaveok: [getter],         writeconcern: [getter] },      topology:        { domain: null,         _events: [object],         _maxlisteners: 10,         s: [object],         bson: [getter],         ismasterdoc: [getter],         poolsize: [getter],         autoreconnect: [getter],         host: [getter],         port: [getter],         emitopen: false,         connecttimeoutms: 30000,         sockettimeoutms: 0 },      dbname: 'abc',      options: { promiselibrary: [object], readconcern: undefined },      namespace: 'abc.ac',      readpreference: { _type: 'readpreference', mode: 'primary', tags: undefined },      raw: undefined,      slaveok: true,      serializefunctions: undefined,      internalhint: null,      collectionhint: null,      name: 'ac',      promiselibrary:        { [function: lib$es6$promise$promise$$promise]         all: [function: lib$es6$promise$promise$all$$all],         race: [function: lib$es6$promise$promise$race$$race],         resolve: [function: lib$es6$promise$promise$resolve$$resolve],         reject: [function: lib$es6$promise$promise$reject$$reject] },      readconcern: undefined } } connected correctly server. connected  server. { s:     { pkfactory:        { [function: objectid]         index: 462263,         createpk: [function: createpk],         createfromtime: [function: createfromtime],         createfromhexstring: [function: createfromhexstring],         isvalid: [function: isvalid],         objectid: [circular],         objectid: [circular] },      db:        { domain: null,         _events: {},         _maxlisteners: 10,         s: [object],         serverconfig: [getter],         buffermaxentries: [getter],         databasename: [getter],         options: [getter],         native_parser: [getter],         slaveok: [getter],         writeconcern: [getter] },      topology:        { domain: null,         _events: [object],         _maxlisteners: 10,         s: [object],         bson: [getter],         ismasterdoc: [getter],         poolsize: [getter],         autoreconnect: [getter],         host: [getter],         port: [getter],         emitopen: false,         connecttimeoutms: 30000,         sockettimeoutms: 0 },      dbname: 'abc',      options: { promiselibrary: [object], readconcern: undefined },      namespace: 'abc.ac',      readpreference: { _type: 'readpreference', mode: 'primary', tags: undefined },      raw: undefined,      slaveok: true,      serializefunctions: undefined,      internalhint: null,      collectionhint: null,      name: 'ac',      promiselibrary:        { [function: lib$es6$promise$promise$$promise]         all: [function: lib$es6$promise$promise$all$$all],         race: [function: lib$es6$promise$promise$race$$race],         resolve: [function: lib$es6$promise$promise$resolve$$resolve],         reject: [function: lib$es6$promise$promise$reject$$reject] },      readconcern: undefined } } **connected correctly server.** 

please why giving error

if want display documents in given collection code should :

mongoclient.connect(url, function(err, db) { assert.equal(null, err); var collection = db.collection('ac').find({},function(err,doc){     if(err)         throw err;     else{         console.log(doc);     } }); console.log("connected correctly server."); db.close(); }); 

this print documents of collection ac. otherwise if directly try print collection metadata printed.