A lightweight view class is provided but there is no default templating method implemented. Because views are minimal it allows for much more freedom to implement views however you would like, and because of this freedom it's possible to write views to more uniquely adapt to a problem. User interactions are done within an events object that allows these interactions to be segregated from the rest of the view code which makes the behavioral aspect of the view easier to read and manage.
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Pro Gives you the freedom to implement views however you want
A lightweight view class is provided but there is no default templating method implemented. Because views are minimal it allows for much more freedom to implement views however you would like, and because of this freedom it's possible to write views to more uniquely adapt to a problem.
User interactions are done within an events object that allows these interactions to be segregated from the rest of the view code which makes the behavioral aspect of the view easier to read and manage.
Pro Can be combined with any library you want
Pro Large community
Backbone has existed longer than most frameworks, and has a large following of users and projects using it as a framework.
Pro You can call underscore.js methods directly on Backbone objects
Backbone collections and models are extended by underscore.js method allowing you to call underscore methods directly on the Backbone objects.
Pro Easy to interface with the API
Backbone provides Model and Collection classes that provide strong analogs to restful resources. These strong analogs allow you to interface more naturally with the API, and makes it easier to write custom behaviors for more complicated API interactions.
Collections provide a variety of powerful manipulation methods that are integrated from the underscore library, that allow you to manipulate, sort, and filter collection data easily.
Pro Easy to implement complex user interaction
Because all the state is managed by Models and Controllers, and they are extendable objects, you can isolate all the state logic onto those objects allowing the rest of the application to not worry about it. The app is simplified to just taking in input to modify the Models and Controllers, and updating the views to reflect them, but none of the state needs to be a concern outside of the Model and Controller classes.
Pro Doesn’t force you into a particular coding style or paradigm
There is no “magic” happening below the surface: the source code is clear, readable and well commented. Backbone is also “lightweight” in the sense that it doesn’t require a ton of buy-in to use. It can be easily integrated into an existing page, and you can choose to only use certain components of the library (Views without Models or Collections, for example). While there are many frameworks that seem to be faster to get started with, Backbone’s lack of surprises, clear documentation, speed & flexibility make it a good fit for all types of apps.
Pro Extendable with plugins
Because Backbone is so simple, and the different components are very well isolated, it is very easy to extend the functionality of Backbone. If you're writing your own extended code it's easy to keep it separated out, and share with the community.
The community also has many plugins already available, which you can pick and choose to use to fit your programming style.
Pro Easy to abstract interaction
All Backbone classes extend an events class that allows for listening and triggering functionality. Because all classes implement events by default it is easier to provide asynchronous communication between objects, and it allows better abstraction of interaction so the event emitting object does not need to know the structure or existence of the receiving object.
Pro Based on web components
Web Components are a collection of specifications released by W3C as a way to reduce the complexity of web apps by creating reusable components. Browser support is currently poor for web components, however Polymer is developed to make web components compatible with modern browsers.
Pro Various basic components
It provides a base component.
Pro HTML markup is not string
HTML markup as it can be a non-string.
Pro CSS is easy to apply
CSS can be applied far more comfortably than React.
Pro Flex layout components
It provides Flex layout components.
Pro Excellent documentation
Polymer guides you as with tools (cli, build environment, app templates,..) as with complimentary documentation on all phases of app development from creation of app as progresive web app to production deployment instructions.
As Polymer is standards based, the whole community around those standards also helping in documentation and support.
Pro Complete web app stack support
Full app stack from data tier to routing, progressive web app, responsive layouts makes no need to seek outside of Polymer ecosystem for application features.
In addition to waste set of mature web components in Polymer Elements along with Vaadin Elements there are thousands of web components in the wild comparable to jQuery plugins set.
Pro API is easy to understand, based on standard
The Polymer APIs are split on application layers and follow standards on all possible ways: Web Components, CSS variables, async API via Promises and so on.
Pro Excellent routing
The router is embedded into CLI for project creation and covers as web as Progressive web app, also fused with Polymer layouts out of the box. The shop template for CLI has a complete solution including the routing.
Pro No need for special debugging tools
The presence od specialized debugging tools are advertised by competitors. The all features of web components are natively supported by browser embedded development tools.
Con Requires more coding compared to other frameworks
Because many features are not provided out of the box, you either have to write more base class code to get those features, or find a plugin that provides them in a way you like.
It does not provide much structure either, things like memory management must be kept in mind by the developer, also the lack of view lifecycle management makes state changes prone to memory leaks.
Con Can easily lead you to spaghetti code
Heavy event-binding can lead to unmanageable spaghetti mess. BB tempts users to overuse it for no reason.
Con No data binding
Backbone does not have data binding support. However, there are some libraries that can be implemented in order to have data binding in Backbone. Such as Epoxy
Con No server-side rendering
Polymer does not support server-side rendering. This results in higher loading times, more HTTP requests and it's not very SEO friendly, since search engines have no way of indexing a page if it's not rendered in the server.