mongo-promise.js

mongoConnect(mongoUrl)
  .then(function(db) {
    var flow = {};
    flow.db = db;
    return flow;
  })
  .then(function(flow) {
    console.log("hello world");
    return flow;
  })
  .then(function(flow) {
    flow.db.close();
  });

not-working.js

mongoConnect(mongoUrl)
  .then(function(db) {
    var customers = db.collection("customers");
    return Q.denodeify(customers.find().toArray);
  })
  .then(function(customers) {
    console.log(customers.length);
  })