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React 18 Features

  • Concurrent React & Automatic Batching
    React can now interrupt, pause, and resume renders for smoother UI responsiveness. Automatic batching groups state updates—even inside promises or setTimeout—to avoid redundant re-renders.Simplilearn.comlegacy.reactjs.orgFreeCodeCamp

  • Transitions (startTransition, useTransition)
    Allows you to mark UI changes that are non-urgent (e.g., loading search results), keeping the UI snappy by prioritizing urgent updates (like typing) over transitions.legacy.reactjs.orgFreeCodeCamp

  • Suspense on the Server
    Enables component-level code splitting and streaming server-side rendering. You can show parts of your UI immediately even if other parts are still loading.FreeCodeCamp

  • Strict Mode Enhancements
    In development, components may be mounted, unmounted, and remounted to help detect side-effects—aiming for more resilient state management.Simplilearn.comFreeCodeCamp

  • New Hooks

    • useId: Generates stable unique IDs for SSR setups.acil.in
    • useDeferredValue: Defers updates from expensive state changes.acil.in
    • useSyncExternalStore: Helps integrate with external data stores.acil.in
    • useInsertionEffect: For injecting CSS styles before layout.

React 19 Features

React 19 builds on its predecessor, adding more ergonomic APIs for modern web development:

  • Actions & useActionState
    A new pattern to manage async state updates (like form submissions) in a structured way, with automatic handling of pending states and updates.WikipediaReddit

  • Enhanced Hooks for Forms

    • useFormStatus: Lets child components access form metadata (e.g., pending state, method) without prop drilling.ReactTelerik.com
    • useOptimistic: Enables optimistic UI updates—instantly showing tentative changes while async operations are in-flight.ReactTelerik.com

  • New use() Hook & More
    Developers can now read promises or context using the new use API.RedditFreeCodeCamp

  • Form Enhancements
    React DOM now supports passing functions directly as action and formAction props, tying into the new Actions feature and form reset APIs.React

  • Custom Elements & Metadata Support
    React 19 provides first-class support for Web Components (custom elements), improved document <head> metadata control (like <title>, <meta>), stylesheet, async script loading, and resource preloading.Wikipedia+1Reddit+1

  • Hydration & Context Improvements
    Enhanced hydration diffing (more robust SSR hydration), improved Context handling, cleaning up refs, better error reporting, and support for async scripts and preloaded assets.Wikipedia

  • Hydration Bug Fix
    Hydration errors caused by browser extensions (like Grammarly) injecting unexpected DOM elements are now fixed.Reddit

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