Ranked in these QuestionsQuestion Ranking
Pro Easy data binding
Pro Easy to learn
Has a low entry barrier and an easy learning curve. It's especially easy to learn for beginners.
Pro Built in templating
Bindings in Knockout can also be used to control the generated structure of the HTML. There are bindings provided to allow for iteration and conditionals. The structure of the html reflects the structure of the data so iterative elements are bound to arrays in the data model. Having the HTML structure maintained by bindings keeps the templating simple, easy to read, and maintain.
Knockout also allows for string based templating so you can use whatever templating library you prefer.
Pro Legacy browser support
Supports a large number of browsers, including IE6.
Pro Great documentation
The excellent tutorials with built-in exercises are a great learning experience, even for people without prior MVVM and data binding experience.
Pro Lightweight and plays nicely with other libraries
Pro Dynamic models help with keeping the code simple and clean
Models in Knockout can be watched to keep the page data up to date by using observable objects. The observables notify Knockout when data is changed and automatically updates the page when this happens. By having Knockout maintain this relation, it keeps the front end code cleaner and simpler, and by enforcing a consistent pattern with observables the methodology can be more robust.
Pro Very flexible
One can do a lot of things and it keeps self references and other types of loops under control.
Pro It's only a library
Knockout does one thing, and does it well. It doesn't try to take on more than one area. It does MVVM data binding and that is it.
Pro Simple manageable modules
Using components is a great way of breaking up large modules into simpler ones.
Pro Comprehensive documentation
The Sencha documentation is comprehensive, with detailed documentation and a number of examples displaying the various widgets, tools and themes.
Pro Supports MVC and MVVM development
Pro Supports Web and Mobile deployment out of the one framework or codebase
Pro Support for easy theming of applications
Pro Visual Design tool available
The Sencha Architect product allows you to visually build your application, or rapidly prototype a system.
Pro IDE Plugins available
A number of plugins are available for some of the commonly used IDEs (eg: JetBrains, Eclipse, Visual Studio), providing templates, refactoring support, hinting and code completion/generation, as well as management of includes and other time-saving features.
Pro Charting package included
Con Slower than others when amount of objects grows
Knockout has a bad performance when the dealing with large amount of objects. You can see more here.
Con Can become complex once the application grows large
Knockout leaves the application structure to the developer and it can become quite complex and unmanageable in the hands of a beginner once the application grows large and complex.
Con Two way binding requires a little extra work
When allowing users to edit existing data, the two-way binding of observables means you'll need to have to save original values before they're edited, to make comparisons or revert if the user cancels the action.
Con Sencha CMD is bloated and frustrating to work with
To do any meaningful development, you are stuck with CMD. There is a gulp task that will handle the JS concatenation, but there is nothing outside of CMD that can handle theming in their ecosystem.
In addition, CMD is based on Java, and is very heavy to run (600MB+ on Windows 10 to watch for changes in the application and recompile).
Con Sencha CMD (their CLI) is under documented, and out of date
Their latest release of CMD changed some configuration locations, but the documentation was not updated to reflect this. There is no reference guide on the json configuration files, other than the (unfortunate use of) comments in the generated json files.
Con They use proprietary extensions to SASS, making it incompatible with anything but their Fashion processor
On the plus side, you do not have to install ruby alongside CMD for more recent versions of ExtJS. However, their Fashion processor seems to only be available through CMD.
Con Too often breaking changes between versions. They have little concept of backwards compatibility
Compounded by the fact that there are now two "toolkits" in the same "version" of ExtJS, with certain components not existing in one vs the other.
Con The IDE tools are not sold separately - you must purchase the appropriate license pack
You get all the IDE plugins, even if you only need one. They should offer sell them individually, or continue to bundle them with a dev license pack.
Con Difficult to integrate with 3rd party software
Any third party library you wish to include has to be wrapped in some sort of component adapter. You have to do a lot of tweaking to get the build process right if you want the 3rd party lib to be bundled into your application in the right order.
Con Can be expensive
The framework is a commercial package, and the recent decision to start with a minimum of 5 users may rule out smaller developer teams or startups. Recently, they have started a program that allow essentially what are contractors to purchase single licenses, but not individual, independent developers.