json - Nodejs callback hell in foreach -

i have venues data. want how people in here after compress venues data , count data json. code working json result null.

var _venues = _.map(venues.response.venues, function (v) {     checkin.where({             'venuesuniqeid': v.id,             'createddate': {                 $gte: new date().gethours() - 2             }         })         .count(function (err, herenow) {              return new venue({                 'uniqeid': v.id,                 'name': v.name,                 'count': herenow             });         }); }); return r.json(_venues); 

first of all, understanding of map function is: map takes set of inputs , 1-to-1 transform them different. in case, _venues array empty because not returning inside _.map callback.

the way have tackled problem use promises library bluebird or q , leverage .all method. in case _.map not outputting actual _venues _venuepromises later execute , wait array of venues. in other words, because of asynchronous nature of mongoose, output of checkin.where not collection of venues collection of promises.

disclaimer: not use mongoose not sure how integrates either q or bluebird.

var promise = require('bluebird');  var _venuepromises = _.map(venues.response.venues, function (v) {     return checkin.where({             'venuesuniqeid': v.id,             'createddate': {                 $gte: new date().gethours() - 2             }         })         .count(function (err, herenow) {              return new venue({                 'uniqeid': v.id,                 'name': v.name,                 'count': herenow             });         }); });  promise.all(_venuepromises).then(function (actualvenues) {   return r.json(actualvenues); });