What's new in React 18?

The examples in this book are based on React 18. This release doesn't introduce sweeping API changes the way React 16 did. There are, however, two notable changes that we'll cover in more depth in Chapter 13, High-Performance State Updates.

Automatic batching

Batching state updates together drastically improves the performance of React applications because it reduces the number of renders to be performed. React has always had the ability to batch multiple state updates into one state update, but it was limited by where this could happen. Specifically, you could only batch state updates together inside event handler functions. The problem here is that most of our state update code runs in an asynchronous way that prevents automatic batching from happening.

React 18 removes this barrier and allows for automatic state update batching to happen anywhere. In Chapter 13, High-Performance State Updates, you'll see examples that compare how this worked prior to React 18 and what you can expect now.

State transitions

React 18 introduces the notion of a state transition. The idea with state transitions is that the less important state updates that take place in your application should have lower priority than state updates that should happen immediately. In Chapter 13, High-Performance State Updates, we'll explore the new APIs that make setting state update priority a reality in React 18.

It might not seem like much has changed in React 18, but the two major areas that we'll cover have far-reaching consequences for how React applications are implemented going forward. Existing React APIs for this version have mostly been left unchanged so that the React community can quickly adopt this latest major version upgrade without any friction.