I am new to backbone, and I'm here to ask for a little bit of help understanding how I would go about building my current webapp project. I'm developing a modular administration panel for servers. Every single "page" of the panel should be a packaged "module" including controllers, models and views.
The panel will consist of a main layout view being loaded initially, with a basic navigation. When a user clicks on a link on the navigation, a page gets loaded via AJAX into the layout.
(And if this sounds stupid / there is a reason not to do so please tell me :) )
Since others will develop these pages too, and since they are modular, I won't know what models, views and controllers I will be presented with inside the page i load via AJAX.
How would I best go about doing this with backbone?
I'm especially wondering about how I would extend Backbone models etc. dynamically, and how I would manage (for example) the user leaving the page and / or revisiting it later.
Does Backbone provide something I can work with, will I need to hack myself something together, is there a better way of doing things I am missing?
Your thinking around the problems sounds very correct. Make your UI components self contained as possible. Watch this 10 min video to get some more information on UI component best practices.
If you are interested about other important concerns of JavaScript application development, look at BoilerplateJS reference architecture which I published to share my experiences. That contains a similar sample application as you described (menu with component activation).
my recommendations for your UI component activation, deactivation are:
Do not remove/create DOM components. Reuse with hide/show, as your elements will recide in memory even after removing from DOM
Minimize keeping 'state' information on client side. When an user revisit the component, refresh it with a server call and then make it visible (use server as the single truth of state information).
See BoilerplateJS sample component implementations for more details. I know few who use it with BackboneJS (currently it ships with knockoutJS). We will ship a example of it using BackboneJS in v0.2 which is due in a week.
A common modular script loading framework that is used in conjunction with Backbone would be require.js. It might be what you're looking for. Require.js is all about AMD modules, asynchronous modules. Usually each model, collection, view is it's own module that defines the dependencies that particular module needs then loads those modules as needed. It's particularly well suited for large projects where you have lots of individual pieces that need to be mish-mashed together at different points of your application.
You could of course combine multiple backbone elements in a single module (usually I reserve this for Views and specific subviews that would only be used with the parent view) but it's really up to you.
With Backbone, usually the intent is to create single page applications - meaning all the page scaffolding is usually wrapped up as a single file and completely loaded onto the client-side at the get go. The data for each page is then called via ajax and populated as the user navigates and loads different aspects of the application. Is this what you intended in your description?
If you're looking to load different pages that are each individually grabbed form the server, then I'm not sure Backbone is the answer. There are other server-side MVC frameworks that help to accomplish that.
That generally touches on how Backbone is used for this sort of thing.
As for how to extend Backbone models and such, Backbone uses Underscore as a dependency and underscore provides a nice _.extend() function that can easily extend all your objects in pretty much any way you desire. Overriding default functionality, throwing in mixins, it's all pretty painless as far as Backbone goes. As a framework, Backbone is very agreeable when it comes to altering, modifying and customizing every little bit and piece.
As for handling users visiting and revisiting pages, Backbone.router allows you to create URLs that not only point to specific "pages" in your app but also to execute arbitrary code that needs to be executed to get there. Something like a logged in user visiting "mysite/#account" would trigger the router to load certain scripts that bring up that particular view as well as perhaps fetch() necessary data to get that view up and running for the user.
I'm not sure if there are resources out there that give you some kind of basic structure to start with. Most experiences I know of tend to go through the basic tutorials like "Todo List" and work their way up from there. I'm not sure what your experience level is with javascript or programming in general but I started with Backbone AND require when I knew really pretty much nothing. Only a vague notion of what JSON was and a low level understanding of HTTP as in, "it's that thing that gets web pages." That said, I think Backbone was really easy to get for me to start with and it's deepened my knowledge a lot about the whole client-side RESTful type app structure.
There is a really good list out there of the "Todo List" app in many different flavors such as Backbone and Knockout and some others. When deciding on a framework, I basically went through that code comparing all the different frameworks available and selected Backbone because it just seemed to make the most sense to me. I don't regret it. It's a lot of fun and I think the best way to get into it is to just try some demo tutorials.
Take a look at Marionette or Chaplin. Both are build on top of Backbone and provide a structured way to build larger application with Backbone.
Here is tutorial to organize your application as modules using backbonejs
http://backbonetutorials.com/organizing-backbone-using-modules/
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Hope that someone can share their experience with some of the latest emerging backbone.js variants out there.
I have some good experience with backbone/underscore/require in several projects and I will like to take the next step towards more advanced solutions for complex application structure.
I know the following frameworks are available:
Marionette
Geppetto (based on Marionette)
Chaplin, Chaplin - chaplin-boilerplate
Vertebrae
LayoutManager
Thorax
Aura
Luca
Singool
backstack
Backbone UI
hulk
BTW - excellent starting point for big scale project
And probably I missed a few.
There is a short introduction about the differences here:
speakerdeck talk link
but it's very general. I was wondering if someone can share their experience with real life applications using these frameworks.
What is the benefit of choosing one over the other? When will marionette be a better solution over chaplin, or why is vetebrae better for certain applications, for example.
Sure, the obvious answer will be "use whats best for your needs", but I lack of the experience with these frameworks to know their strength/purpose/advantages or preferred scenarios.
Thanks!
Edit 1:
found this post:
Backbone.Marionette vs Backbone-Boilerplate
Edit 2:
Answer by Mathias schafer (Chaplin) by mail:
In short, the current structure is close to version 1.0 since it’s already used in production. We’re not planning to add big new feature or breaking API changes until 1.0.
Marionette is for sure the most comprehensive and stable library out there. It addresses several aspects of JS app development with Backbone. For example, it has a strong view layer which Backbone itself leaves completely void. Of course, you will find that some of the aspects won’t meet your demands and you might feel the need to set up a structure around Marionette.
In contrast, Chaplin focusses on a rather small, but very important aspect of Backbone apps, namely the overall app structure and module lifecycle. In this regard Chaplin is very opionated and is more like a framework than a library (like in “your code calls a library, a framework calls your code”). Chaplin provides some central classes which sit above individual application modules and control the overall app state. This gives your app a conventional structure like Ruby on Rails does it for example.
In Chaplin, you declare some routes which map to controllers, and Chaplin starts the controller once the route match. It also takes care of the disposal of old controllers, and the showing and hiding of main views, which a controller is supposed to create. This is the basic idea, but Chaplin takes care of the ugly details to make this run smoothly.
There are two principals which come along with this structure:
- Modularization, decoupling and sandboxing
- Cross-module communication using Publish/Subscribe and Mediator(s)
Of course these patterns are not new in the software development world, and Chaplin is not the only library which applies them to Backbone.js apps.
Chaplin also provides enhancements for the View layer, for example a highly sophisticated CollectionView, but in total not as much as Marionette with its Regions and Layouts. But it’s relatively easy to write such meta classes using the means Chaplin Views provide.
Most of (all of?) the frameworks that you're looking at solve the same problems, but they do it in slightly different ways with slightly different goals.
I think it's fair to say that all of these projects would solve the problems in these categories:
Provide sensible set of defaults
Reduce boilerplate code
Provide application structure on top of the BackboneJS building blocks
Extract patterns that authors use in their apps
Marionette, which I've been building since December of 2011, has a few very distinct goals and ideals in mind, as well:
Composite application architecture
Enterprise messaging pattern influence
Modularization options
Incremental use (no all-or-nothing requirement)
No server lock-in
Make it easy to change those defaults
Code as configuration / over configuration
I'm not saying none of the other frameworks have these same goals. But I think Marionette's uniqueness comes from the combination of these goals.
Composite Application Architecture
I spent more than 5 years working in thick-client, distributed software systems using WinForms and C#. I built apps for desktop, laptop (smart-client), mobile devices and web applications, all sharing a core functional set and working with the same server back-end many times. In this time, I learned the value of modularization and very rapidly moved down a path of composite application design.
The basic idea is to "compose" your application's runtime experience and process out of many smaller, individual pieces that don't necessarily know about each other. They register themselves with the overall composite application system and then they communicate through various means of decoupled messages and calls.
I've written a little bit about this on my blog, introducing Marionette as a composite application architecture for Backbone:
http://lostechies.com/derickbailey/2011/11/17/introduction-to-composite-javascript-apps/
http://lostechies.com/derickbailey/2011/12/12/composite-js-apps-regions-and-region-managers/
Message Queues / Patterns
The same large scale, distributed systems also took advantage of message queuing, enterprise integration patterns (messaging patterns), and service buses to handle the messages. This, more than anything else, had a tremendous influence on my approach to decoupled software development. I began to see single-process, in-memory WinForms applications from this perspective, and soon my server side and web application development took influence from this.
This has directly translated itself in to how I look at Backbone application design. I provide an event aggregator in Marionette, for both the high level Application object, and for each module that you create within the application.
I think about messages that I can send between my modules: command messages, event messages, and more. I also think about the server side communication as messages with these same patterns. Some of the patterns have made their way in to Marionette already, but some haven't yet.
http://lostechies.com/derickbailey/2011/07/19/references-routing-and-the-event-aggregator-coordinating-views-in-backbone-js/
http://lostechies.com/derickbailey/2012/04/03/revisiting-the-backbone-event-aggregator-lessons-learned/
http://lostechies.com/derickbailey/2009/12/23/understanding-the-application-controller-through-object-messaging-patterns/ (WinForms code, but still applicable)
Modularization
Modularization of code is tremendously important. Creating small, well encapsulated packages that have a singular focus with well defined entry and exit points is a must for any system of any significant size and complexity.
Marionette provides modularization directly through it's module definitions. But I also recognize that some people like RequireJS and want to use that. So I provide both a standard build and a RequireJS compatible build.
MyApp = new Backbone.Marionette.Application();
MyApp.module("MyModule", function(MyModule, MyApp, Backbone, Marionette, $, _){
// your module code goes here
});
(No blog post available for this, yet)
Incremental Use
This is one of the core philosophies that I bake in to every part of Marionette that I can: no "all-or-nothing" requirement for use of Marionette.
Backbone itself takes a very incremental and modular approach with all of it's building block objects. You are free to choose which ones you want to use, when. I strongly believe in this principle and strive to make sure Marionette works the same way.
To that end, the majority of the pieces that I have built in to Marionette are built to stand alone, to work with the core pieces of Backbone, and to work together even better.
For example, nearly every Backbone application needs to dynamically show a Backbone view in a particular place on the screen. The apps also need to handle closing old views and cleaning up memory when a new one is put in place. This is where Marionette's Region comes in to play. A region handles the boilerplate code of taking a view, calling render on it, and stuffing the result in to the DOM for you. Then will close that view and clean it up for you, provided your view has a "close" method on it.
MyApp.addRegions({
someRegion: "#some-div"
});
MyApp.someRegion.show(new MyView());
But you're not required to use Marionette's views in order to use a region. The only requirement is that you are extending from Backbone.View at some point in the object's prototype chain. If you choose to provide a close method, a onShow method, or others, Marionette's Region will call it for you at the right time.
http://lostechies.com/derickbailey/2011/12/12/composite-js-apps-regions-and-region-managers/
http://lostechies.com/derickbailey/2011/09/15/zombies-run-managing-page-transitions-in-backbone-apps/
No Server Lock-in
I build Backbone / Marionette apps on top of a wide variety of server technologies:
ASP.NET MVC
Ruby on Rails
Ruby / Sinatra
NodeJS / ExpressJS
PHP / Slim
Java
Erlang
... and more
JavaScript is JavaScript, when it comes to running in a browser. Server side JavaScript is awesome, too, but it has zero effect or influence on how I write my browser based JavaScript.
Because of the diversity in projects that I built and back-end technologies that my clients use, I cannot and will not lock Marionette in to a single server side technology stack for any reason. I won't provide a boilerplate project. I won't provide a ruby gem or an npm package. I want people to understand that Marionette doesn't require a specific back-end server. It's browser based JavaScript, and the back-end doesn't matter.
Of course, I fully support other people providing packages for their language and framework. I list those packages in the Wiki and hope that people continue to build more packages as they see a need. But that is community support, not direct support from Marionette.
https://github.com/derickbailey/backbone.marionette/wiki/Available-packages
Easily Change The Defaults
In my effort to reduce boilerplate code and provide sensible defaults (which is an idea that I directly "borrowed" from Tim Branyen's LayoutManager), I recognize the need for other developers to use slightly different implementations than I do.
I provide rendering based on inline <script> tags for templates, using Underscore.js templating by default. But you can replace this by changing the Renderer and/or TempalteCache objects in Marionette. These two objects provide the core of the rendering capabilities, and there are wiki pages that show how to change this out for specific templating engines and different ways of loading templates.
With v0.9 of Marionette, it gets even easier. For example, if you want to replace the use of inline template script blocks with pre-compiled templates, you only have to replace one method on the Renderer:
Backbone.Marionette.Renderer.render = function(template, data){
return template(data);
};
and now the entire application will use pre-compiled templates that you attach to your view's template attribute.
I even provide a Marionette.Async add-on with v0.9 that allows you to support asynchronously rendering views. I continuously strive to make it as easy as possible to replace the default behaviors in Marionette.
Code As Configuration
I'm a fan of "convention over configuration" in certain contexts. It is a powerful way of getting things done, and Marionette provides a little bit of this - though not too much, honestly. Many other frameworks - especially LayoutManager - provide more convention over configuration than Marionette does.
This is done with purpose and intent.
I've built enough JavaScript plugins, frameworks, add-ons and applications to know the pain of trying to get conventions to work in a meaningful and fast way. It can be done with speed, but usually at the cost of being able to change it.
To that end, I take a "code as configuration" approach to Marionette. I don't provide a lot of "configuration" APIs where you can provide an object literal with static values that change a swath of behaviors. Instead, I document the methods that each object has - both through annotated source code and through the actual API documentation - with the intent of telling you how to change Marionette to work the way you want.
By providing a clean and clear API for the Marionette objects, I create a situation where replacing the behavior of a specific object or Marionette as a whole is relatively simple and very flexible. I sacrifice the "simple" configuration API calls for the flexibility of providing your own code to make things work in the way that you want.
You won't find a "configure" or "options" API in Marionette. But you will find a large number of methods that each serve a very specific purpose, with clean signatures, that make it easy to change how Marionette works.
I'm currently using backbone with the layout manager module and handlebars as templating engine and I found really easy to set up a little application using an already existing Grails backend. Before starting using layout manager I read about Marionette and Chaplin and both seemed to me really powerful but complex. Then I remembered why I originally choosed backbone.js: simplicity. All those frameworks are adding what backbone has left out by design. I'm not saying that a framework is bad, but if I need something more complex I'll try other projects, like ember.js or sproutcore, since they have a unique codebase, written with a goal in the mind of their developers. Here we have frameworks on top of another one. Of course, backbone is a backbone not only for building applications, but also for writing some more powerful library, but the only thing I think is really poor with it is the view layer, since is missing a layout manager and the possibility of nesting views. With layout manager that gap is filled quite well.
So, my answer to your question is: start from using backbone as is, and ask yourself what is missing and what were your expectations about the framework. If you find there are too many things left out by backbone, then go and search for them in the other frameworks and choose the one is nearest your needs. And If you are still not confident in the choice, maybe backbone is not for you and you have to look some other solution (ember.js, sproutcore, ExtJs, JavaScript MVC are all good). If you have experience in writing client apps, you don't really need experience on all the framework out there to choose the right one (for you, of course)
I have studied the various frameworks build with Backbone.js and built the Vertebrae for a project at HauteLook. The project goals included... dynamic script loading, AMD module format, dependency management, build with mostly open source libraries, organize code in packages, optimize and build for one or many single page apps, host on fully cached server, e.g. no server-side scripting using only an API for data, and the funnest for me, use behaviour driven development for the project. There is a description on the project at : http://www.hautelooktech.com/2012/05/24/vertebrae-front-end-framework-built-with-backbone-js-and-requirejs-using-amd/
Our Problem:
Selected libraries (jQuery, Underscore.js, Backbone.js, RequireJS, Mustache) provide module loading, dependency management, application structure (for models, collections, views and routes), asynchronous interactions with API, various utilities and objects to manage asynchronous behaviors, e.g. (Promises) Deferreds, Callbacks. The remaining logic needed to complete the framework includes:
an object (model) to manage state of the single-page application;
a layout manager to present, arrange/transition and clear views, and
controllers which respond to routes, get/set application state, and hand off work to layout manager.
Our Solutions (implemented in Vertebrae):
Application State Manager -
The application manager stores data in memory and also persists data in browser storage to provide a resource for common data/metadata. Also provides data (state) to reconstruct the page views based on previous interactions (e.g. selected tab, applied filters). The application state manager provides a strategy for resources to retrieve state. Meant to act as a state machine.
Layout Manager -
The layout manager has one or many views as well as document (DOM) destinations for each (rendered) view. A page may transition between many views, so the layout manager keeps track of view states, e.g. rendered, not-rendered, displayed, not-displayed. You may use the layout manager to lazy load and render (detached) views that a site visitor is very likely to request, e.g. tab changes on a page. The transition between view states is managed by this object. An entire layout may be cleared so that view objects and their bindings are removed, preparing these objects for garbage collection (preventing memory leaks). The layout manager also communicates view state with controller(s).
Controller -
A controller object is called by a route handler function, and is responsible for getting relevant state (application models) to generate a page (layout), (also responsible for setting state when routes change). The controller passes dependent data (models/collections) and constructed view objects for a requested page to the layout manager. As a side-effect the use of controllers prevents the routes object from becoming bloated and tangled. A route should map to a controller which then kicks off the page view, keeping the route handling functions lean.
The Todos app is hosted both in dev mode and optimized on Heroku...
http://vertebrae-framework.herokuapp.com/
http://vertebrae-optimized.herokuapp.com/
Many of the concepts in the other frameworks are borrowed, e.g. the need to destory views to preview memory leaks as pointed out by Derick Bailey - http://lostechies.com/derickbailey/ ; the Layout Manager by Tim Branyen http://tbranyen.github.com/backbone.layoutmanager/
In summary, Backbone.js is meant to be a tool in your application the Backbone.js library does not provide all the architecture you will need to build an application, but does provide great interactions with an API and solid code structure for... Views (act like controllers too) and your data layer Models and Collections, and finally Routes. We built Vertebrae to meat the goals of our project, and decided to extract the code as a framework for others to use, learn, or whatever.
The answer to your question in my opinion is to learn from all the frameworks and use what you need to meet your goals, if you find that your project goals fit closely with one of the frameworks built with Backbone then great, otherwise built your own framework there are great examples being shared by the community. Or if you find yourself a bit lost in the direction of your application then choose something more opinionated and structured perhaps Ember.js. The great thing is there are a good assortment of choices to help you code using an (MVX) MVC like pattern with JavaScript.
I developed the Luca framework while working at BenchPrep where we used it to develop several large single page apps on top of the backbone.js library.
I had worked with ExtJS for several years prior and have stolen my favorite concepts from that framework such as the component driven architecture where you develop your views as standalone components and then join them together with other components using container views. And since it is heavily based on configuration, developing an app in Luca feels a lot like describing an object with JSON.
One advantage to this approach is the ability to re-use components across several apps or in different places in your app, with with only minor changes using Backbone's extend. It is also very easy to experiment with many different layouts / presentations of components by making only minor tweaks to the JSON configuration.
In addition to a wide range of helper / utility functions, Luca Ships with many higher level Backbone derivatives that you can piece together in any way imagineable to build a complex UI.
Views, Components, Containers
Augmented Model, View, Collection, Router classes
Configuration options that facilitate communication between Models, Collections, Views, the Application and its respective managers.
Containers ( Split / Column Layout, Grid Layout, Tab View, Card / Wizard View )
FormView with all of the standard field components, and helpers for syncing with a Backbone.Model
GridView, for generating scrollable grid elements from a Luca.Collection
CollectionView, for generating views based on a collection
Toolbars / Buttons
Twitter Bootstrap Styles and Markup For Free
Luca plays very well with the Twitter bootstrap framework. Simply by setting Luca.enableBootstrap = true, and including the CSS, your components ( such as the tab views, the toolbars, buttons, forms, fields, grids, etc ) will automatically use Twitter Bootstrap compatible markup and CSS class conventions.
Uses the Grid system for layout, and responds to most of the bootstrap base css classes in an intelligent way
Luca.Viewport and GridLayout components are setup to work with bootstrap's responsive, fluid, or static grid systems.
Aims to provide a one to one match for twitter bootstrap components, to represent them as configurable Backbone Views
The Application Component
Backbone.Model based state machine provides getter / setter methods and attribute change events as a style of application control flow
Integrated Controller component which hides / shows pages of the app in response to Backbone.Router or State Machine events
Integrated Collection Manager which keeps track of the collections you have created, allows you to scope them, group them, assign default parameters to them
A Socket Manager which is an abstraction layer on top of websocket services that makes push as easy as Backbone.Event
A Keyboard Event router which triggers named key events on components which care to respond to such events
Collection and Model Enhancements
Collections are based on backbone-query, which provides a querying interface very similar to mongoDb
enable a local storage Backbone.sync simply by setting collection.localStorage = true
automatic population of collections whose data is bootstrapped on page load
cached methods / computed properties. cache the result of collection methods, and expire the cache in response to change / add / remove events on the collection or its models
computed properties on the models. build attributes based on complex function, and automatically update the computed value in response to changes
Events and Hooks
Luca components are more liberal with the events they emit compared to the stock Backbone components. They will emit events like before:initialize, after:initialize, before:render, after:render, activation, first:activation, deactivation, first:deactivation, and this allows you to more finely tune the behavior of your components. Plus, by defining an event in the #hooks porperty on your view, it will automatically call a similarly named function for you if it exists. This prevents a lot of callback style code which improves readability.
You can also configure the Luca.Events class to publish the events to a global publish / subscribe channel, which makes building a large application easier and aids in inter module communication.
The Ruby Gem
Luca was developed specifically while working against Rails and Sinatra APIs and because of this is currently optimized for a specific stack, but it in no way locks you into a specific server.
Luca comes distributed as part of a Ruby Gem configured to work on the asset pipeline, or as a downloadable JS file.
You are not required to use Rails, or Sinatra. But if you do, I have included a lot of useful things:
Files with the .luca extension get processed as HAML with JST style variable interpolation. ( equivalent to .jst.ejs.haml ) by the asset pipeline
A Test Harness for browser, or headless Jasmine based Unit Tests along with many Backbone and Underscore test helpers.
An API endpoint for the development toolset that ships with Luca ( more on this later )
An API endpoint that allows you to use Redis as a schemaless storage engine for Luca.Collection with minimal configuration
The Development Tools
Luca applications can enable an in browser coffeescript console with Luca specific helpers and commands that aid in monitoring, inspecting, debugging Luca applications and components
With the help of the Rails Gem, and Luca's CodeMirror based component editor, you can edit the source code of the Luca Framework as well the application specific components directly in the browser, using Coffeescript. You will see immediate feedback in response to your edits, with the instances of effected objects being refreshed with the updated prototype, and you can save your changes to disk.
The Component Tester is a live sandbox for playing with the components that make up your application in isolation. It provides you with tools for modifying the component's prototype, setting up its dependencies, and configuring the component. The component will re-render immediately every time you make an edit. You can view and edit the markup that the component generates, as well as the CSS directly in the browser and see your changes immediately. This makes it a very valuable experimentation tool.
The Component Tester will soon integrate with Jasmine so you can view the results of your component unit tests in real time as you edit their code
Luca is a work in progress, but maintains a stable API ( not yet 1.0 ) and has been used in several large production apps. It is definitely a very opinionated framework, but I am working on making it more modular. I am actively working on the documentation and sample components.
I’m a co-author of Chaplin and I’ve written an in-depth comparison between Chaplin.js and Marionette.js:
http://9elements.com/io/index.php/comparison-of-marionette-and-chaplin/
This is not a “shootout” but tries to explain both approaches in a balanced way.
When I gloss over the backbone.js site, I'm not sure what is it trying to do.
It seems somewhat popular, but why should I want to learn it? What will it do for me? Why was it made? What problem does it solve?
I find the question perfectly valid and from my point of view there is nothing wrong with inquiring about the potential use cases of a library/toolkit.
What Backbone.js does (so do several other javascript mvc implementations) is that it provides a means of organizing the code into a modular pattern known as MVC pattern which is all about separating your code into three loosely coupled layers:
Model layer dealing purely with data and associated operations
View layer being the presentational aspects
Controller layer being the binding glue layer
(different frameworks deal with this differently : Backbone implementation of controller layer comprises of client side routing capabilities).
So, on the whole backbone provides you an infrastructure using which you can deal with data through models which contain encapsulated within them the data and associated validations, which can be observed ie. you can bind events to change events.
The View layer is mostly left for the user to separate the ui into manageable isolated sections.
Here are some problems that Backbone solves for me in the JS/HTML space:
Separation of Concerns (SoC)
Composability
Testability
Component Model
Abstraction
That is not to say that this is the ONLY system that does this. There are others. Backbone does a pretty good job of helping with these things, though.
From backbonejs.org
It's all too easy to create JavaScript applications that end up as
tangled piles of jQuery selectors and callbacks
And that's exactly what backbone does, a series of callbacks on model changes and jQuery selectors to bind events.
So to answer the question, it solves nothing only to provide a way (the backbone way) of structuring code with some slight automation in the REST side of things.
we have a rich client application written in WPF/WCF and are intending to create a companion website in ASP.net (using MVC if possible).
I've been asked to figure out how much of our current codebase, we can reuse (by a separate team) - and I have little to no experience with ASP.net.
We will reuse our domain model, but is there any point in separating out the WPF-specific parts of our ViewModels and reuse the WPF-agnostic parts in MVC? Does it even follow the same paradigms? We use RelayCommands exclusively for commanding, so it would be easy to wrap the contained methods in something ASP.net specific... But how about UI-specific things - e.g. does ASP.net use INotifyPropertyChanged - or how does it handle UI-updates?
For me it wouldn't make any sense. Your models should contain all of your important business logic code and should be the point of greatest reuseability. Your view models should contain presentation logic only, and as this is so different for a desktop and web app, it doesn't make sense to reuse these.
MVC does not use any binding mechanism for UI updates, as web apps are stateless by nature. You will actually most likely end up using view models for your MVC app, but in MVC these act as simple data transfer objects (DTOs) for providing data to the views for rendering for each HTTP request. Once the view is rendered, you would need to go back to the server to update the view model and rerender the view.
Alternatively, you can of course update the UI client side with scripting. Knockout.js is a nice JS library for client side view model/view binding.
I can't directly answer your specific question because it depends highly on your application and the way your existing view-model is written but the question you raise is an interesting one.
On the one hand, the logic that the view-model contains very little view-specific code is a tantalizing argument for reuse. On the other hand, the view-model very clearly serves the needs of the view and expecting it to serve the needs of a different view could be problematic.
In the end all we can give are guidelines. You certainly don't want a monolithic view-model with ifdefs or ifs all over the place. You could refactor common functionality into base classes -- that's the object-oriented way -- but without good unit tests it's sure to break something in your already working code. But not doing that means having distasteful cut-and-paste code that is almost the same and likely to diverge creating a maintenance nightmare.
Perhaps a practical approach is to assume you'll need a whole new view-model but to review your existing view-model for code you can push down into the model before your start, thereby making the view-model as small as possible. Then at some point, maybe after you get a prototype working, you could attempt a merge to see if it is practical and what issues arise. If it can work, take those issues into account as you continue implementation and then plan the two tasks according to your needs.