It seems like Backbone.Radio provides 2 new abstractions - mands and requests. They're pretty much identical to Backbone.Events, except that they can have only 1 subscriber. Is that it, and if so what advantage do they provide over events?

I plan on using Backbone.Events/Radio with React.js, if that helps.

It seems like Backbone.Radio provides 2 new abstractions - mands and requests. They're pretty much identical to Backbone.Events, except that they can have only 1 subscriber. Is that it, and if so what advantage do they provide over events?

I plan on using Backbone.Events/Radio with React.js, if that helps.

• javascript
• backbone.js
• marionette
• backbone-events

2 Answers 2

I have not actually used Backbone.Radio but do make extensive use of Backbone.wreqr https://github./marionettejs/backbone.wreqr which provides an almost identical mand service.

In my usage the difference between events and mands is:

For events to work the sender and receiver of an event must both exist and have a reference to each other and the receiver must be in a position to deal with the event properly. This can often be problematic in a fully asynchronous browser environment where different parts of your application are running at the same time.

Commands allow you to decouple the sender and receiver. One object, lets say a View A, can simply send mand 'update_user_details'.

My second Object View B sets up a mand handler for 'update_user_details' which will change the user details on the screen.

But what if View B does not yet exist, or is not yet rendered. In the event listener pattern you would have to make sure View A exists, that it passes a reference to itself to View B and then you attach an event listener in View B.

With mands it is not a problem, View A sends a mand, if no-one has set a handler then nothing bad happens, the mand just does nothing.

When View B turns up, totally independent of View A, it sets a handler and will respond to all future mands.

Just a final note about intent:

The event pattern can be thought about in this way: I, View A have just done something, anyone that is interested (the event listeners) can do what they like about it, I View A don't care what you do.

In the mand pattern: I View A want someone to do something, I don't care who does it, I just want it done right.

Channels. The key difference with Backbone.Radio over plain vanilla Backbone.Events that I have seen is that it allows you to setup channels to which your code can 'tune in' e.g. from the documentation:

var userChannel = Backbone.Radio.channel('user');

This means that logical functions or apps in your code can emit and handle events only on a specific channel - even if you emit events with the same name, if they're on different channels you won't get cross-contamination. This ties in nicely with the principles behind separation of duties in your code.

The other other difference, and IMHO it's subtle, more to do with elegance of coding than any real functionality difference, is that if you're telling something to respond to an event then it's really a Command, and Backbone.Radio allows you to separate these kinds of event into that type. Similar logic applies to the Requests type.

For pleteness...

The docs also explain that a Channel is an object that has all three types of messages (Events, Commands and Requests) mixed in. You mix it into an object (I use Marionette so I'm mixing into an instance of Marionette.Object) using Underscore/Lo-Dash's .extend():

_.extend(objectToBeExtended, Backbone.Radio.Requests);

And the same for Commands of course. The syntax for events is different as that's baked into Backbone itself so the second parameter is just Backbone.Events.