What is React Fiber?
React Fiber is the core algorithm behind React's rendering engine, introduced to enable incremental rendering and improve responsiveness for complex UIs. Fiber replaces the older stack-based algorithm, allowing React to pause, abort, and resume work as needed, making updates smoother and more efficient.
How Does React Fiber Work?
Fiber represents each element in the React tree as a Fiber node, which contains information about the component, its state, props, and relationships (parent, child, sibling). The Fiber architecture enables React to break rendering work into units, process them asynchronously, and prioritize updates based on urgency (e.g., user input vs. background data).
Fiber Node Structure
- Type: The kind of component (function, class, host, etc.)
- Key: Unique identifier for reconciliation
- StateNode: The actual instance (DOM node or class instance)
- Props/State: Current and pending values
- Flags: Indicate what work needs to be done (update, placement, etc.)
- Alternate: Points to the work-in-progress version of the node
Workflow
- Reconciliation: React builds a new Fiber tree based on changes in state or props.
- Work Loop: The Fiber engine processes nodes, yielding to the browser when needed to keep the UI responsive.
- Commit Phase: Once all work is complete, changes are committed to the DOM.
Why is Fiber Important?
- Performance: Enables React to handle large, complex updates without blocking the main thread.
- Prioritization: Allows React to prioritize urgent updates, improving user experience.
- Concurrency: Lays the foundation for features like Concurrent Mode and Suspense.
- Debugging: Understanding Fiber helps diagnose rendering issues and optimize components.
- Interuptible Rendering: Via Double buffering thorugh current and work-in-progress trees
Visualizing Fiber
Below is a simplified diagram of Fiber nodes and their relationships:
graph TD
A["Root Fiber"]
A -->|child| B["Component Fiber 1
Type: FunctionComponent
Key: null
StateNode: Instance
Props: Object
State: Object
Flags: Update
Alternate: WIP Fiber"]
B -->|sibling| C["Component Fiber 2
Type: HostComponent div
Key: 'item1'
StateNode: DOM Node
Props: Object
State: null
Flags: Placement"]
B -->|child| D["Child Fiber
Type: Generic"]
C -->|return| A
D -->|return| B
B -->|alternate| E["WorkInProgress Fiber
(Clone for updates)"]
subgraph "Fiber Properties"
F["Common Properties:
- pendingProps
- memoizedProps
- memoizedState
- subtreeFlags"]
end
Conclusion
Mastering React Fiber is essential for advanced React development. It empowers you to build high-performance, scalable applications and leverage the latest React features with confidence.