node.js - Register callback and return document -

this first experience nodejsand mongo. handling database query handlers in seperate js file, exported module in file, handles user requests. want search (findone) user document collection table, , return callee. cannot figure out how register callback , return document, once query execution completes..

here code, call method:

var record = mongodatahandler.getuserrequestobject(credentials.email, ""); 

how change call, such should like:

mongodatahandler.getuserrequestobject(credentials.email, "", function (result){  //handle result response here }); 

here getuserrequestobject, in js file (mongodatahandler.js):

var mongoclient = require('mongodb').mongoclient     , format = require('util').format; var assert = require('assert'); var ds = require('../../server/datasources.json'); var dbmongoconnectorurl = ds.mongodbdev.url;  module.exports = { getuserrequestobject : function(email, number){         var documentobj = null;         mongoclient.connect(dbmongoconnectorurl, function(err, db) {             if (err) throw err;             console.log("connected database");             var cursor = db.collection('userrequestcode').find({"email": "someemail@gmail.com"}).sort( { _id: -1} ).limit(1);             cursor.each(function(err,doc) {                 if (err) documentobj = {status:500, resp:err};                 if (doc != null){                     console.dir(doc);                     documentobj = {status:200, resp:doc};                     return;                 }             });         });         return documentobj;     } } 

the object returned (documentobj) null. because not registered callback function.

how should register callback here, retrieved document collection works asynchronously?

just add argument function , treat function (there's no additional syntax, pretend it's function):

getuserrequestobject : function(email, number, my_own_callback){          /* .. lots of code .. */          // return documentobj;         my_own_callback(documentobj); // how it's done }