Polymer has templates with data binding to DOM Elements. source
Ranked in these QuestionsQuestion Ranking
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.
Con Slow performance in mobile
Since most mobile web browsers don't have a very powerful JS engine, Polymer can be a little slow for mobile devices.
Con Lack of browser support
Due to web components being so new, there is still a lot of issues with browser compatibility. Though Polymer has solved some of these compatibility issues with polyfills, there is still a lot of bugs and unpredictability.
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.