Now that you have some grasp of React elements, we can explain React components, which are JavaScript functions or ES6 classes that accept arbitrary inputs (props) and return the React elements ...

ECMAScript 2015 (or ES6) is the next big thing and front end developers should start learning it now, not later.

No examples using ES6 syntax. All of the examples use ES5 syntax, which feels kludgy after working with better language ergonomics for years.