This library is very highly preferable, and the famous library. Many other famous libraries are built on top of the jQuery. So, this is the starting point and must knowable library for a web developer.
Few words from official jQuery which describe more about it.
This library is built on top of the jQuery. If you want to add user rich control, then this library provides you great controls like a date picker, accordion, dialog and more.
This library popular across major devices like Mobile, Tablet, desktop and more which support touch friendly UI framework. As a part of this library, It provides amazing controls to for great amazing touch experience with attractive graphics specially on Mobile and Tablet.
So, are you planning to build native applications for mobile and tablet, if yes, then this library “jQouery Mobile Framwork” will give a comfort zone to build with well-known platforms like PhoneGap & Worklight.
It supports rich and responsive spectacles and editor user interfaces with a clean fundamental data model. “KO” will be more easily assumed if you are having practice in MVVM apps, RUBY on Rails, ASP .NET MVC or other MV* technologies. Any time you have sections of the UI that update dynamically (e.g., changing depending on the user’s actions or when an external data source changes), KO can help you implement it more simply and maintainable.
These days this is very popular framework among the developers, which works on all platforms. This framework is majorly using CSS to make web responsive on all platforms.