AngularJS

AngularJS is a JavaScript framework that is used in the development of web applications. It was developed by Google, and has been open source since 2010, and it's a top choice for developers when building sites that use JavaScript. Other pros of using AngularJS include server performance gains and the ability to prototype applications faster. Some of the downsides of using AngularJS include the need to have supporting JavaScript for the library to function, the difficulty of learning how to use the library by new developers, and it's difficult to debug.

Angular JS

ReactJS

ReactJS is a JavaScript library that specializes in UI development. It was developed by Facebook, and it's extremely popular due to it using Virtual DOM, which is a program that functions like the DOM in the browser, but it stores the visual representation of a UI in it's memory. Some benefits of using ReactJS include the ease of learning and using, the ability to reuse components, and how easy it is to test code. Some cons of ReactJS include the poor, or even lack there of, documentation regarding ReactJS. In addition, ReactJS only focuses on UIs, so additional resources are needed for backend development.

ReactJS

PolymerJS

PolymerJS is a JavaScript library that allows developers to create their own HTML elements, that can then be used on their other HTML pages. Upsides of using PolymerJS include the capability for developers to create their own plugins, as well as it's high performance on browsers like Chrome and Safari. However, it can be time consuming to develop a lot of elements, custom elements can reduce website performance, especially on mobile, and it is incompatible with Internet Explorer.

PolymerJS

Conclusion

While the few JavaScript libraries mentioned above have a wide range of uses, there are dozens of unique libraries that allow developers to make their time working with JavaScript easier.