React 18 Released: Concurrent Rendering and Automatic Batching

What happened

React 18 became available on March 29, 2022. Its central change was the introduction of a concurrent renderer, a behind-the-scenes update to React's core rendering model that unlocks a set of new capabilities. Concurrency is opt-in: existing apps upgrade and behave as before until they start using concurrent features.

Concurrent rendering

The defining property of Concurrent React is that rendering is interruptible. React can start rendering an update, pause, continue later, or even abandon an in-progress render, while guaranteeing the UI stays consistent by deferring DOM mutations until the whole tree is ready. This lets React prepare new screens in the background without blocking the main thread, keeping the interface responsive to input during large rendering tasks.

Automatic batching

React 18 extended automatic batching so that multiple state updates are grouped into a single re-render even inside promises, timeouts and native event handlers, not just React event handlers as before. In practice this means fewer unnecessary renders for the same code, with no changes required from developers.

Transitions and Suspense on the server

The release added the transitions API, with startTransition and useTransition, to distinguish urgent updates such as typing from non-urgent ones such as rendering search results, so the UI stays responsive. It also added support for Suspense during server-side rendering and introduced streaming SSR through new APIs like renderToPipeableStream, alongside new client APIs createRoot and hydrateRoot.

Why it mattered

React 18 laid the foundation that later releases built on. Most existing components worked without changes, but the concurrent renderer, transitions and streaming SSR gave library authors and frameworks the primitives to build smoother, more responsive experiences. It was also the base on which React Server Components would later stabilise in React 19.

Related on Skillo

See also: React 19's Actions and stable Server Components.

Sources

• React v18.0 (official React blog)

Published date reflects the original event date (2022-03-29). This article is original Skillo editorial written from the sources above; facts were verified in September 2026.