Blocking Rendering (Traditional React)

• React processes updates one at a time and can’t be interrupted once it starts.
• If a render takes a long time (e.g., complex components, heavy calculations), the entire app becomes unresponsive until the render is complete.
• Even minor interactions like typing or clicking can feel laggy during heavy rendering.
• Rendering happens in a synchronous and non-prioritized way — no matter how important the update is.

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Concurrent Rendering (Concurrent Mode)

• React can pause, interrupt, and even abandon a render if something more important happens.
• Rendering is split into small chunks and spread across frames, keeping the app feeling smooth and responsive.
• Urgent updates (like typing) are prioritized, while less urgent work (like lazy-loading a sidebar) happens in the background.
• Rendering becomes asynchronous and priority-based, allowing React to adapt better to real-world user interactions.

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Quick Comparison Table:

Aspect	Blocking Rendering	Concurrent Rendering
Interruptible?	❌ No	✅ Yes
Priority System?	❌ No	✅ Yes
Responsiveness	❌ Can freeze UI	✅ Stays responsive
Update Type	Synchronous	Asynchronous
Typical Usage	Classic React apps	Modern apps with heavy interactivity

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