I'm new to Backbone.js, and I'm trying to figure out where state variables should live. My use case:
I have an application that provides a reading interface for a book (I know, classic example, right?). My models are Book
and Page
with collection classes for each. The structure of the application looks roughly like this (forgive the ASCII visio):
+------------+
| Controller |
+------------+
| Views Models
| +--------------+ +----------------+
|-| IndexView |------| BookCollection |
| +--------------+ +----------------+
| |
| +--------------+ +----------------+
+-| BookView |------| Book |
+--------------+ +----------------+
| |
| +--------------+ |
|-| TitleView |-+ |
| +--------------+ | +----------------+
| +-| Page |
| +--------------+ | +----------------+
+-| PageView |-+
+--------------+
That is, the Controller
instantiates and coordinates two views, IndexView
and BookView
, backed by the models. The BookView
instantiates and coordinates a set of subviews (there are actually more than shown here).
State information includes:
My question is, where should this state information live? Possible options include:
The models, which could be state-aware. This makes some sense, since they're intended to store data and views could listen for state changes, but it doesn't seem like this fits the intended Backbone.js pattern, and wouldn't always make sense (e.g. turning image on in the PageView
should apply to all pages, not just the current one)
A special singleton model intended to hold state information. Again, makes sense, easy to listen to, all the views could bind to it - but again, this seems outside standard MVC.
The views, who are responsible for the UI state - but this would require views to be aware of each other to get state info, which seems incorrect
The controller, which should route the application between states - this makes sense, but it implies a slightly odd round trip, e.g. User selects "Show Images" --> View event listener is called --> View informs Controller --> Controller updates state --> Controller updates View
(rather than the simpler User selects "Show Images" --> View event listener is called --> View updates
)
I guess in some ways this is a generic MVC question, but I'm having trouble getting my head around it. What part of the application should be responsible for saving the current state?
UPDATE: For future reference, I used a global singleton State model for this problem. The UI flow goes like this:
app.State
app.State
- they're essentially specialized views that display and react to URL changesapp.State
and update accordinglyMy app is Open Source - you can see the code on Github. The relevant piece here is the State model, which I've extended to deal with (de)serializing state for the URL.
Don't limit your Backbone apps to Backbone constructs. If you find that your app needs some functionality that doesn't fit well into one of Backbone's constructs, don't shoehorn it into one just for the sake of keeping everything in Backbone.
I've found this backbone boilerplate to be helpful in this respect. It sets up modules for you and provides you with an app object that extends Backbone.Events (like in the previously-linked article). This app object can be used to store instantiated models, views and controllers/routers, and you should feel free to add your own non-backbone modules to the app object, to take care of responsibilities that don't fit perfectly into one of the Backbone constructs.