Unlocking the Power of React Fiber
Ever wondered what happens when you call ReactDOM.render(<App />, document.getElementById('root'))? Behind the scenes, React builds a complex DOM tree and renders your application on the screen. But have you ever stopped to think about how it actually works?
The Old Way: The Stack Reconciler
Before React Fiber, the stack reconciler was the default reconciler for React. This algorithm traversed the component tree recursively, updating the DOM tree accordingly. However, this approach had its limitations. Every update would trigger a complete rerender of the entire subtree, causing dropped frames and a poor user experience.
The Problem with Dropped Frames
Dropped frames occur when the browser takes longer than 16ms to render a frame. This can happen when the React renderer takes too long to update the DOM tree. The result is a janky, unresponsive user interface.
Enter React Fiber
React Fiber is an internal engine change that makes React faster and smarter. It’s an asynchronous reconciler that can pause, resume, and restart rendering work on components as new updates come in. This allows React to break away from the limits of the synchronous stack reconciler and fine-tune rendering components for optimal performance.
How React Fiber Works
React Fiber uses a singly-linked list of fiber nodes to represent the component tree. Each fiber node holds the component’s state, props, and underlying DOM element. When an update occurs, React creates a new fiber node and performs a parent-first, depth-first traversal of the tree. The render phase builds a new tree based on the updates, and the commit phase swaps the root pointers of the current tree and workInProgress tree.
The JavaScript Execution Stack
To understand how React Fiber works, it’s essential to understand how the JavaScript engine handles execution contexts. The JavaScript engine uses a stack data structure to handle function calls and returns. However, when it comes to asynchronous events, the engine uses a queue data structure to handle the event loop.
The Fiber Node
A fiber node represents a unit of work with its own virtual stack. It holds the component’s state, props, and underlying DOM element. The fiber node also has a priority field, which indicates the priority of the work represented by the fiber.
The Render Phase
During the render phase, React builds a new tree based on the updates. It starts with the root node and recursively traverses the tree, creating new fiber nodes as needed. The render phase is where React performs the reconciliation algorithm, determining what changes need to be applied to the DOM tree.
The Commit Phase
Once the render phase completes, React moves on to the commit phase. Here, it swaps the root pointers of the current tree and workInProgress tree, effectively committing the changes to the DOM tree.
Conclusion
React Fiber is a powerful engine change that makes React faster and more efficient. By understanding how it works, you can unlock the full potential of React and build faster, more responsive applications.