One of the most consequential new features of React is Hooks—functions that extend the behavior of functional React components. Hooks are used to "hook into" the React component machinery from your React components. Instead of relying on classes to build components that have state or that rely on executing side effects when the component is mounted, you can use the React Hooks API to pass functions that handle these cases.
The end result is having more flexibility with how you're able to compose React components since functions are more easily shared between modules than component class methods are. Hooks are the future of how React components are assembled, which will have a big impact on the third edition of this book, where there's a new chapter devoted to Hooks, as well as updated code in all chapters from the second edition.
You can read more about Hooks here: https://reactjs.org/docs/Hooks-intro.html.
