React 18 introduced the concurrent rendering foundation plus new APIs like createRoot, automatic batching, transitions, and new hooks. Explain the key changes and why they matter to users and developers.
What's new in React 18?
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The Core Idea
React 18 is about a new rendering foundation (concurrency) plus APIs that make apps feel more responsive without changing every component. It also adds new hooks and stricter dev checks to surface unsafe effects.
Change | Why it matters | Example |
|---|---|---|
New root API | Enables concurrent features and improved scheduling |
|
Automatic batching | Fewer renders across async boundaries | Multiple state updates in timeouts/promises |
Transitions | Keep urgent input responsive during heavy updates |
|
Deferred values | Let expensive UI lag slightly behind fast input |
|
Suspense + streaming SSR | Faster time-to-first-byte and incremental rendering | Stream HTML and hydrate as data arrives |
New hooks for ids and external stores | Stable ids for a11y and safer subscriptions |
|
Migration notes
Move to createRoot to opt into React 18 behavior, and audit effects for StrictMode double-invocation in dev. Use transitions for non-urgent updates and keep effects idempotent.
Summary
React 18 adds concurrent rendering foundations, automatic batching, transitions/deferred values for responsiveness, stronger Suspense/streaming capabilities, and new hooks like useId. The goal is smoother UI without blocking urgent updates.
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