init-mongo-geo.js

exports.db = function(fn){
  MongoClient.connect(mongoUrl, function(err, db) {
    if(err){throw err;}
    global.nss = {};
    global.nss.db = db;
    global.nss.db.collection('listings').ensureIndex({'coordinates':'2dsphere'}, function(err, indexName){
      console.log('Connected to MongoDB');
      fn();
    });
  });
};

listings.find({'coordinates':{$nearSphere:{$geometry:{type:'Point', coordinates:[loc.lat * 1, loc.lng * 1]}}, $maxDistance : 250000}}).toArray