ReactJS tries to solve the problem from the View layer. It can very well be defined and used as the V in any of the MVC frameworks. It's not opinionated about how it should be used. It creates abstract representations of views. It breaks down parts of the view in the Components. These components encompass both the logic to handle the display of view and the view itself. It can contain data that it uses to render the state of the app.

To avoid complexity of interactions and subsequent render processing required, React does a full render of the application. It maintains a simple flow of work.

React is founded on the idea that DOM manipulation is an expensive operation and should be minimized. It also recognizes that optimizing DOM manipulation by hand will result in a lot of boilerplate code, which is error-prone, boring, and repetitive.

React solves this by giving the developer a virtual DOM to render to instead of the actual DOM. It finds difference between the real DOM and virtual DOM and conducts the minimum number of DOM operations required to achieve the new state.

React is also declarative. When the data changes, React conceptually hits the refresh button and knows to only update the changed parts.

This simple flow of data, coupled with dead simple display logic, makes development with ReactJS straightforward and simple to understand.

Who uses React? If you've used any of the services such as Facebook, Instagram, Netflix, Alibaba, Yahoo, E-Bay, Khan-Academy, AirBnB, Sony, and Atlassian, you've already come across and used React on the Web.

In just under a year, React has seen adoption from major Internet companies in their core products.

In its first-ever conference, React also announced the development of React Native. React Native allows the development of mobile applications using React. It transpiles React code to the native application code, such as Objective-C for iOS applications.

At the time of writing this, Facebook already uses React Native in its Groups and Ads Manager app.

In this book, we will be following a conversation between two developers, Mike and Shawn. Mike is a senior developer at Adequate Consulting and Shawn has just joined the company. Mike will be mentoring Shawn and conducting pair programming with him.