How React elements work
In this book, we assume that you are familiar with components and their instances, but there is another object you should know about if you want to use React effectively – the element. Elements are lightweight immutable descriptions of what should be rendered, while components are more complex stateful objects responsible for generating elements.
Whenever you call createClass, extend Component, or declare a stateless function, you are creating a component. React manages all the instances of your components at runtime, and there can be more than one instance of the same component in memory at a given point in time.
As mentioned previously, React follows a declarative paradigm, and there’s no need to tell it how to interact with the DOM; you declare what you want to see on the screen, and React does the job for you. One of the tools that makes this process more expressive and readable is JSX, which allows you to write HTML-like syntax directly...