Wonderful async Example

restaurant-api.js

var countUser = function (callback) {
	database.getCollection('User').find(function (err, nbUsers) {
		if (err) return callback(err);
		return callback(null, nbUsers.length);
	});
};
var countRestaurantByCity = function(city, callback) {
	database.getCollection('Restaurant').count({'adresse.ville': city}, function (err, nbR) {
		if (err) return callback(err);
		return callback(null, nbR);
	});
};
var countRestaurant = function (callback) {
	database.getCollection('Restaurant').count(function (err, nbR) {
		if (err) return callback(err);
		return callback(null, nbR);
	});
};


exports.testAsyncSeries = function (req, res, next) {
	var city = req.query.city;
	async.series({
		nbUsers:async.apply(countUser),
		nbR:async.apply(countRestaurant),
		nbRC: async.apply(countRestaurantByCity, city)
	}, function (err, results) {
		if (err) return res.send(err);
		return res.send(results);
	})
};

exports.testAsyncWaterfall = function (req, res, next) {
	async.waterfall([
		function(callback) {
			database.getCollection('User').find({role:20})
				.select('_id login')
				.limit(10)
				.exec(function(err, users) {
					return callback(err, users);
				})
		},
		function(users, callback) {
			async.map(users, function(user, mappingUserRestaurant){
				database.getCollection('Restaurant').count({'pro': user._id})
					.exec(function(err, nbRestaurants) {
						var userObj = {};
						userObj[user.login] = nbRestaurants;
						return mappingUserRestaurant(err, userObj);
					})
			}, function(err, result) {
				return callback(err, result);
			})
		}
	], function (err, result) {
		res.json(result);
	});
};