dispatch.js

var distance = require('google-distance');
var _ = require('lodash');

module.exports = function (pubnub) {
  pubnub.subscribe({
    channel: "dispatch",
    message: onNewDispatch
  });

  function onNewDispatch(message) {
    const payload = JSON.parse(message);
    var store = findClosestStore(payload.stores);
    var rider = findRider(store);
    var riderMessage = {
      "delivery_id": payload.delivery_id,
      "store": store
    };

    pubnub.publish({
      channel: "riders."+rider.id
      message: riderMessage,
      callback: function (res) {
        console.log("Succesfully dispatched delivery "+payload.delivery_id+" to "+rider.id);
      }
    });
  }

  function distanceBetween(origin, destination, callback) {
    var distanceInMetres;
    distance.get(
      {origin: origin, destination: destination},
      function (err, data) {
        if(err) return console.log(err);
        distanceInMetres = data.distanceValue;
      }
    );
    return distanceInMetres;
  }

  function findStore(stores, destination) {
    // here we want to find the closest store
    stores = _.map(stores, function (store) {
      store["distance"] = distanceBetween(store.address, destination);
      return store;
    });
    stores = _.sortBy(stores, 'distance');
  }

  function findRider(store) {
    var riderIds;

    pubnub.here_now({
      channel: 'riders.*',
      callback: function (m) {
        riderIds = m.uuids;
      }
    });
  }
};

var async = require('async');
var stores = [] //fill with something
function distanceBetween(destination, store, callback) {
    distance.get({ origin: store.address, destination: destination }, function (err, data) {
        if(err) return callback(err);
        store.distanceValue = data.distanceValue;
        return callback(null, store);
      }
    );
  }

function getDistances = function(err, results){
        //results should be a collection with your real distance values in store.distanceValue
}
async.map(stores, distanceBetween.bind(null, destination), getDistances)