React 19 is already here.

But surprisingly, many React developers are still not familiar with the most useful features introduced in React 18.

That's exactly why I created this guide, to help you clearly understand the powerful features React 18 provides and how they improve real-world React applications.

React 18 is the most significant release since React 16 introduced Hooks. At its core, React 18 is about one big idea: concurrent rendering , and everything else flows from it.

This guide walks through every major feature and API introduced in React 18, with practical code examples you can use today.

Table of Contents

Concurrent Rendering

New Root API — createRoot

Automatic Batching

startTransition and useTransition

useDeferredValue

Suspense Improvements

useId

useSyncExternalStore

useInsertionEffect

Strict Mode Changes

React Server Components

Migration Guide

1.…