async-callbacks.js

'use strict';

var express = require('express')
, async = require('async');

var app = express();

function getAges (callback) {
  callback(null, ['23', '43']);
}

function getUsers (callback) {
  callback(null, ['jane', 'john']);
}

function getData (callback) {
  async.parallel({
    ages: getAges,
    users: getUsers
  }, callback);
}

app.get('/', function (req, res, next) {
  
  function onData (err, data) {
    if (err) {
      res.status(500).json({
        msg: 'error'
      });
    } else {
      res.json(data);
    }
  }

  getData(onData);
});

app.listen(3001, function (err) {
  if (err) {
    throw err;
  }

  console.log('listening on 3001');
});