React Fiber: Analysis, Operation, and Effects

How Fiber Works

Fiber optimizes the UI update process through three main phases:

Render Phase (Can be interrupted)

Determines what changes need to be made.
Traverses the Fiber tree using the Reconciliation algorithm.
Compares the old and new Virtual DOM (diffing).
Creates a list of changes (work-in-progress tree).

🛑 This phase can be interrupted if the browser needs to handle critical tasks like scrolling or animations.

Commit Phase (Cannot be interrupted)

Applies changes from the Fiber tree to the actual DOM.
Runs componentDidMount, componentDidUpdate, useEffect.

✅ Since React pre-calculates all changes in the Render Phase, the Commit Phase is very fast.

Work Loop & Scheduler

React uses a scheduler to control execution time.
The scheduler assigns priority levels to tasks.
If there is a high-priority task (e.g., user interaction), React pauses the Render Phase and handles that task first.
Uses mechanisms like requestIdleCallback or MessageChannel to optimize scheduling.

Effects and Benefits of Fiber

Feature	React Stack (Old)	React Fiber (New)
Performance	Blocking (synchronous)	Non-blocking (can pause)
UI Updates	Entire component tree	Partial updates
Animation & Gesture	Laggy when loading	Smoother, UI prioritized
Concurrent Mode	Not supported	Supported (future)
Error Handling	No Error Boundary	Supports Error Boundary
Memory Usage	Higher	More optimized

Real-world Applications of Fiber

Suspense & Lazy Loading: Load components smoothly.
Concurrent Mode: Enhances UI experience by prioritizing critical tasks.
Better Animation: React can pause rendering to prioritize animations.

Conclusion

React Fiber makes React more powerful by optimizing UI updates, improving performance, and reducing lag in complex interfaces. This is a major advancement that helps React compete with other frameworks like Vue and Svelte. 🚀