node.js - Why i am not getting the data in first call to my REST API -

i making call rest api on making first call returning empty array , on second call returning desired result.here files.

mongodb.js connecting mongodb database

var mongoclient =require('mongodb').mongoclient; var dburl = 'mongodb://localhost:27017/test';   module.exports.connect = function connect(callback){     mongoclient.connect(dburl, function(err, conn){         /* exports connection */         if(err)         {             callback(err);console.log(err)         }         else         {             callback(undefined,conn.collection('person'));             //console.log(conn)         }      }); }; 

getusers.js retrieving documents database

const mongodb = require('.././mongodb/mongodb');  var v=[]; module.exports.getuser=function(callback) {     mongodb.connect(function(err,db)     {         if (err)         {             console.log(err)         }         else         {             data(db,function (docs) {                 //console.log(v)                 callback(v)             })            // console.log(v)          }     }); } function data(db,callback) {     db.find().foreach((docs)=>{                 v.push(docs)     })     callback(v); } 

server.js starting server

const express = require('express'); const bodyparser = require('body-parser') const getusers = require('./users/getusers'); const insertusers = require('./users/insertusers'); const findusers = require('./users/findusersemail'); const delusers=require('./users/deleteusers') const moduser=require('./users/updateuser') const app = express(); app.use(bodyparser.json()) app.get('/person', (req, res) => {   console.log(res.statuscode)     if(res.statuscode==200)     {         getusers.getuser(function (userlist){             res.json(userlist);             console.log(userlist);          })      }}) app.listen(4569,()=>console.log('server has started on 4501')) 

because data function calls callback before data returned. correct implementation should be:

const mongodb = require('.././mongodb/mongodb');  module.exports.getuser = function(callback) {   mongodb.connect(function(err, db) {     if (err) {       console.log(err);     } else {       data(db, callback);     }   }); }  function data(db, callback) {   db.find().toarray((err, docs) => callback(docs)); } 

you can see global variable v not used @ all.

by way, should follow nodejs convention implement callback function:

callback(err[, ...args]) 

skipping error argument give lot of pain when code base grows, when need integrate third-party libraries.