React Fiber
Fiber is a complete rewrite of React's internal rendering engine (introduced in React 16).
Problem with the old engine (Stack Reconciler)
The previous reconciler traversed the component tree recursively and synchronously - it could not be interrupted. With a large tree this blocked the main thread and caused UI jank.
What Fiber changed
- Reconciliation is split into small units of work.
- Work can be paused, cancelled, or resumed.
- Task prioritization: animations matter more than background data updates.
This opened the path to concurrent rendering
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High priority: user input, animations
Low priority: data fetching renders, transitionsSummary: Fiber is the architectural foundation for
Suspense,Transitions,useDeferredValue, and all of Concurrent React.
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