It provides a base component.
Ranked in these QuestionsQuestion Ranking
Pro Provides built in support for UI widgets
Huge amount of widgets available, also easy to build custom widgets by extending the available components.
Pro Professional support available
If you buy a license you can get professional support and premium forums. Support has short contact times and solutions are of great value.
Pro Well documented
ExtJS' documentation is very detailed and helpful. All concepts and parts of the framework are thoroughly explained.
Pro IDE plugins available
Plugins are available for JetBrains, Eclipse and Visual Studio.
Pro Easy reusability of code
By using the packages and custom components, code can be reused very simply.
Pro Flat learning curve
Pro Forum support
Forum support is available.
Pro Excellent design tools
Eg: Sencha Architect.
Pro Developer friendly integrated tools
Sencha Cmd, Sencha Inspector and some IDE plugins etc., are the tools which helps developers to speed up their development.
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 Flex layout components
It provides Flex layout components.
Pro CSS is easy to apply
CSS can be applied far more comfortably than React.
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.
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 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 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 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 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.
Con Completely unreliable with regard to licensing and pricing
That ExtJs is expensive is not the problem, but what they did is started completely free, then switched the licensing model when they had profited from the community. Also, they suddenly switched from a single user license to a minimum of 5 users.
Ext-JS is not for free, it comes with a license.
Con Large footprint
The library is almost 500Kb in size hence significantly affects your page load time.
Con Expensive licensing
ExtJS is free for use in open source projects, but you have to use the unstable version which is riddled with bugs. Furthermore, to build a project (even if it's open source), you have to buy their proprietary tools.
For commercial projects, it costs $665 for a license.
Con No real support
You only get a limited premium questions that could be answered via the support and if the issue is too large then you might lose all your credits (it has a credit system for support) in one question.
In addition the replies in premium forum are sometimes less thought of than you would get in stackoverflow.
Con Lots of bugs
The community is very small and this is because the licencing is very expensive. Therefore not many people to test the framework and give feedback in order to fix.
They try to do everything in house which means that a small company (linkedin shows about 100 employees) tries to imitate something very large.
The scaling problems lead to lots of bugs and instability.
Con No web-workers
ExtJS does not take into account the asynchronous nature of todays web browsers where you can do heavy stuff on the background.
Con Tooling is poor
They had a GUI architect tool, but that tool never was up to date with the current framework version. Now they even seem to have abandoned the whole architect app. Also, to build a ExtJs app you have to use their tool (and then you have to pay, from that moment ExtJs is no longer GPL). But this tool also has lots of bugs.
Con Steep learning curve
ExtJs is a very opinionated framework. You have to do it the ExtJs way or it's the highway. So, a lot of time, things in your own opinion doesn't make sense or don't work in the way you expect it.
Con Quantity yes, quality no
There is a large amount of source code that can be useful and indeed all the samples works flawlessly.
When you try to get into more complex scenarios you will find yourself in situations where things just do not work as expected. You will have to do manual work.
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.