React in Patterns

React in patterns is a free book that serves as an introduction to React. Even though it's tied to React, it's a compelling read if you do anything with user interfaces.
It is nice that we may think about every React component as a black box. It has its own input, lifecycle and output. It is up to us to compose these boxes. And maybe that is one of the advantages that React offers. Easy to abstract and easy to compose.
Instead exploring React's API surface like most guides do, it gradually explains the idea of a component model, and how to deal with state & data flow. 

Thinking in components, and more specifically learning how to separate your applications concerns with components, has changed the way I tackle interfaces for the modern web.