Even more decoupled than the original - pass dependencies in as args so that they can be easily changed later

decoupling-dependencies

document.addEventListener("DOMContentLoaded", function(event) {
  
  /*
  Later you can easily change this to any other PubSub library you like.
  
  var _pubSub = PubSub;
  
  or you can even wrap it to define your own API. This way, later on 
  you can still continue to use _ps.sub and _ps.pub even if you change
  out the library defining that behaviour. Let's go with the latter. 
  */
  var _ps = {
    pub: PubSub.publish,
    sub: PubSub.subscribe
  }
  
  var orderModule = (function(ps) {
    var orders = {},
      EST_DELIVERY = 'current estimated delivery time',
      estimatedDeliveryTime;
 
    ps.subscribe(EST_DELIVERY, function(msg, data) {
      console.log(msg);
      estimatedDeliveryTime = data;
    });
 
    return orders;
  })(_ps);
 
  var deliveryModule = (function(ps) {
    var deliveries = {},
      EST_DELIVERY = 'current estimated delivery time';
 
    deliveries.getEstimatedDeliveryTime = function() {
      var estimatedDeliveryTime = 1; // Hard-coded to 1 hour, but likely an API call.
 
      ps.publish(EST_DELIVERY, estimatedDeliveryTime);
    };
 
    return deliveries;
  })(_ps;
 
  deliveryModule.getEstimatedDeliveryTime();
});

Typo on line 41:
})(_ps;
should be
})(_ps);