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Last updated on Sep 29, 2023
Last updated on Sep 21, 2023
React Fiber is a reimplementation of React's core algorithm, designed to enhance the user interface's responsiveness and renderability. The term "fiber" refers to a unit of work, a fundamental concept in the fiber architecture. The React team introduced React Fiber to improve the reconciliation phase of the React application, making it more efficient and effective.
React Fiber is not a feature but an ongoing reimplementation of React's reconciliation algorithm. The react fiber reconciler, a critical part of the fiber architecture, is responsible for updating the user interfaces. It does this by comparing the current tree (the tree data structure representing the current state of the UI) with the work in progress tree (the tree data structure representing the new state of the UI).
The fiber architecture is a term coined by the React team to describe the new reconciliation algorithm in React Fiber. This architecture is designed to enable incremental rendering, allowing React to split rendering work into chunks and spread it out over multiple frames.
In the fiber architecture, each react element corresponds to a fiber node. The fiber node is a JavaScript object that contains information about the react element, its rendered output, and its relationships with other fibers in the fiber tree. The fiber tree, in turn, represents the structure of the React application.
The fiber architecture also introduces the concept of a virtual stack frame, a data structure that allows React to pause, resume, and reuse previously completed work. This is a significant departure from the traditional call stack model, where the stack frame is discarded once the function execution is completed.
1 // A simple React component represented as a fiber node 2 const FiberNode = { 3 type: 'div', 4 key: 'myDiv', 5 props: { 6 children: [ 7 { type: 'p', props: { children: 'Hello, world!' } }, 8 ], 9 }, 10 }; 11
React Fiber aims to improve the responsiveness and renderability of user interfaces in React applications. It does this by introducing a new reconciliation algorithm that can split rendering work into chunks and spread it out over multiple frames. This process, known as incremental rendering, allows React to prioritize high-priority updates (such as user interactions) over low-priority updates (such as offscreen rendering).
Another main goal of React Fiber is to provide a more predictable and controllable rendering environment. With the fiber architecture, developers can specify the priority of different updates and control when and how these updates are applied to the DOM tree. This makes it easier to optimize the rendering process and ensure a smooth user experience.
React Fiber also aims to support new features and improvements in the React ecosystem, such as the concurrent mode and the Suspense component. These features rely on the fiber architecture's ability to pause, resume, and reuse previously completed work.
React Fiber and the Virtual DOM are both core concepts in React, but they serve different purposes and work in different ways.
The Virtual DOM is a lightweight representation of the actual DOM tree. It allows React to determine the minimum number of updates required to synchronize the actual DOM tree with the desired state of the user interface. This process, known as reconciliation, is performed by the React reconciliation algorithm.
On the other hand, React Fiber is a reimplementation of the reconciliation algorithm. It introduces a new data structure (the fiber node) and a new execution model (the fiber architecture) to enable incremental rendering and improve the responsiveness and renderability of user interfaces.
While the Virtual DOM focuses on minimizing the number of updates to the actual DOM tree, React Fiber focuses on managing the rendering work and controlling when and how these updates are applied. This makes React Fiber more flexible and powerful than the Virtual DOM, especially in complex and dynamic user interfaces.
React Fiber works by creating a fiber tree that mirrors the component tree of a React application. Each fiber node in the fiber tree represents a React element and contains information about the element, such as its type, props, state, and relationships with other elements.
During the rendering process, React Fiber traverses the fiber tree and creates a unit of work for each fiber node. The unit of work represents the tasks that need to be performed for the fiber node, such as creating a new DOM element, updating an existing DOM element, or unmounting an old DOM element.
React Fiber uses a scheduling algorithm to prioritize the units of work and decide which ones should be performed first. High-priority units of work, such as user interactions and animation frames, are performed before low-priority units of work, such as offscreen rendering.
Once all the units of work have been performed, React Fiber enters the commit phase, where it applies the changes to the DOM tree. This is done in a single pass to minimize the impact on the rendering performance.
1 // A simple example of how React Fiber works 2 function App() { 3 const [count, setCount] = React.useState(0); 4 5 return ( 6 <div> 7 <p>You clicked {count} times</p> 8 <button onClick={() => setCount(count + 1)}> 9 Click me 10 </button> 11 </div> 12 ); 13 } 14
The fiber tree plays a crucial role in React Fiber. It is a tree data structure that mirrors the component tree of a React application. Each fiber node in the fiber tree represents a React element and contains information about the element, such as its type, props, state, and relationships with other elements.
The fiber tree is used by React Fiber during the rendering process. It is traversed to create units of work for each fiber node, and these units of work are then prioritized and performed based on their priority.
The fiber tree also plays a crucial role in the commit phase of React Fiber. During the commit phase, React Fiber traverses the fiber tree and applies the changes to the DOM tree. This is done in a single pass to minimize the impact on the rendering performance.
A fiber node is a JavaScript object that represents a React element in the fiber tree. It contains information about the React element, such as its type, props, state, and relationships with other elements.
Each fiber node also contains additional fields that are used by React Fiber during the rendering process. These fields include the fiber's priority, the fiber's previous output, and pointers to the fiber's parent, sibling, and child fibers.
The fiber node is a fundamental concept in React Fiber. It is used to represent the structure of the React application and manage the rendering work. By manipulating the fiber nodes, React Fiber can control when and how the updates are applied to the DOM tree.
1 // An example of a fiber node 2 const fiberNode = { 3 type: 'div', 4 key: 'myDiv', 5 props: { 6 children: [ 7 { type: 'p', props: { children: 'Hello, world!' } }, 8 ], 9 }, 10 // Additional fields used by React Fiber 11 priority: 1, 12 previousOutput: null, 13 parent: null, 14 sibling: null, 15 child: null, 16 }; 17
The unit of work is another fundamental concept in React Fiber. It represents the tasks that need to be performed for a fiber node, such as creating a new DOM element, updating an existing DOM element, or unmounting an old DOM element.
The unit of work is created during the rendering process when React Fiber traverses the fiber tree. Each fiber node generates a unit of work, and these units of work are then prioritized and performed based on their priority.
The concept of the unit of work allows React Fiber to split the rendering work into chunks and spread it out over multiple frames. This enables incremental rendering, which improves the responsiveness and renderability of user interfaces in React applications.
The React Fiber reconciler is a part of the React Fiber architecture responsible for updating the user interfaces. It does this by comparing the current tree with the workinprogress tree and determining the minimum number of updates required to synchronize the two trees.
The reconciler works in two phases: the render phase and the commit phase. During the render phase, the reconciler traverses the workinprogress tree and creates a unit of work for each fiber node. These units of work are then prioritized and performed based on their priority.
During the commit phase, the reconciler applies the changes to the DOM tree. This is done in a single pass to minimize the impact on the rendering performance.
The reconciler also handles the lifecycle methods of class components and the hooks of functional components. It calls these methods and hooks at the appropriate times during the rendering process.
1 // An example of a class component with lifecycle methods 2 class MyComponent extends React.Component { 3 componentDidMount() { 4 console.log('Component did mount'); 5 } 6 7 componentDidUpdate() { 8 console.log('Component did update'); 9 } 10 11 componentWillUnmount() { 12 console.log('Component will unmount'); 13 } 14 15 render() { 16 return <div>Hello, world!</div>; 17 } 18 } 19
Host components are the actual DOM elements that are rendered by React components. They are the lowest level of components in a React application and are managed directly by the React Fiber reconciler.
During the rendering process, the reconciler creates a unit of work for each host component. This unit of work represents the tasks that need to be performed for the host component, such as creating a new DOM element, updating an existing DOM element, or unmounting an old DOM element.
The reconciler also handles the lifecycle methods of host components. It calls these methods at the appropriate times during the rendering process, ensuring that the host components are updated correctly and efficiently.
React Fiber uses a tree data structure to represent the structure of a React application. This tree, known as the fiber tree, mirrors the component tree of the application. Each node in the fiber tree, known as a fiber node, represents a React element and contains information about the element, such as its type, props, state, and relationships with other elements.
The fiber tree is used by the React Fiber reconciler during the rendering process. It is traversed to create units of work for each fiber node, and these units of work are then prioritized and performed based on their priority.
The fiber tree also plays a crucial role in the commit phase of React Fiber. During the commit phase, the reconciler traverses the fiber tree and applies the changes to the DOM tree. This is done in a single pass to minimize the impact on the rendering performance.
React Fiber uses multiple frames to spread out the rendering work over time. This is done to improve the responsiveness and renderability of user interfaces in React applications.
During the rendering process, React Fiber creates a unit of work for each fiber node. These units of work are then prioritized and performed over multiple frames, based on their priority.
High-priority units of work, such as user interactions and animation frames, are performed before low-priority units of work, such as offscreen rendering. This allows React Fiber to respond quickly to user interactions and maintain a smooth animation frame rate, even in complex and dynamic user interfaces.
React's reconciliation algorithm is a core part of React Fiber. It is responsible for comparing the current tree with the workinprogress tree and determining the minimum number of updates required to synchronize the two trees.
The reconciliation algorithm works in two phases: the render phase and the commit phase. During the render phase, the algorithm traverses the workinprogress tree and creates a unit of work for each fiber node. These units of work are then prioritized and performed based on their priority.
During the commit phase, the algorithm applies the changes to the DOM tree. This is done in a single pass to minimize the impact on the rendering performance.
The reconciliation algorithm also handles the lifecycle methods of class components and the hooks of functional components. It calls these methods and hooks at the appropriate times during the rendering process, ensuring that the components are updated correctly and efficiently.
Child fibers are an essential part of the fiber tree in React Fiber. Each fiber node in the fiber tree can have one or more child fibers, which represent the child elements of the corresponding React element.
During the rendering process, React Fiber traverses the fiber tree and creates a unit of work for each fiber node, including the child fibers. These units of work are then prioritized and performed based on their priority.
Child fibers also play a crucial role in the commit phase of React Fiber. During the commit phase, React Fiber traverses the fiber tree, including the child fibers, and applies the changes to the DOM tree. This is done in a single pass to minimize the impact on the rendering performance.
1 // An example of a fiber node with child fibers 2 const fiberNode = { 3 type: 'div', 4 key: 'myDiv', 5 props: { 6 children: [ 7 { type: 'p', props: { children: 'Hello, world!' } }, 8 ], 9 }, 10 // Child fibers 11 child: { 12 type: 'p', 13 props: { children: 'Hello, world!' }, 14 // Additional fields used by React Fiber 15 priority: 1, 16 previousOutput: null, 17 parent: fiberNode, 18 sibling: null, 19 child: null, 20 }, 21 }; 22
The React team played a pivotal role in developing React Fiber. They recognized the limitations of the existing reconciliation algorithm and embarked on a complete rewrite of the algorithm, resulting in the creation of React Fiber.
The team's goal was to create a reconciliation algorithm that could support incremental rendering, allowing React to split rendering work into chunks and spread it out over multiple frames. This would improve the responsiveness and renderability of user interfaces in React applications.
The React team also wanted to provide a more predictable and controllable rendering environment. With React Fiber, developers can specify the priority of different updates and control when and how these updates are applied to the DOM tree.
The fiber reconciler is a key component of React Fiber. It is responsible for the process of reconciliation, which involves comparing the current tree and the workinprogress tree to determine the minimum number of updates required to synchronize the two trees.
The fiber reconciler works in two phases: the render phase and the commit phase. During the render phase, the reconciler traverses the workinprogress tree and creates a unit of work for each fiber node. These units of work are then prioritized and performed based on their priority.
During the commit phase, the reconciler applies the changes to the DOM tree. This is done in a single pass to minimize the impact on the rendering performance.
The fiber reconciler also handles the lifecycle methods of class components and the hooks of functional components. It calls these methods and hooks at the appropriate times during the rendering process.
React Native is a popular framework for building mobile applications using React and JavaScript. It uses the same reconciliation algorithm as React, which means it also benefits from the improvements introduced by React Fiber.
With React Fiber, React Native can provide a more responsive and smoother user experience. The incremental rendering feature of React Fiber allows React Native to prioritize high-priority updates, such as user interactions and animation frames, over low-priority updates, such as offscreen rendering.
React Fiber also provides a more predictable and controllable rendering environment for React Native. Developers can specify the priority of different updates and control when and how these updates are applied, making it easier to optimize the performance of React Native applications.
Lifecycle methods are a key feature of class components in React. They allow developers to control the behavior of a component at different stages of its lifecycle, such as when it is created, updated, or destroyed.
In React Fiber, lifecycle methods are handled by the fiber reconciler. The reconciler calls these methods at the appropriate times during the rendering process, ensuring that the components are updated correctly and efficiently.
For example, the componentDidMount method is called after a component is mounted (i.e., created and inserted into the DOM tree). The componentDidUpdate method is called after a component is updated. The componentWillUnmount method is called before a component is unmounted (i.e., removed from the DOM tree).
The initial render phase is the first phase of the rendering process in React Fiber. During this phase, the fiber reconciler traverses the workinprogress tree and creates a unit of work for each fiber node. These units of work represent the tasks that need to be performed for the fiber nodes, such as creating a new DOM element, updating an existing DOM element, or unmounting an old DOM element.
The initial render phase is also when the reconciler handles the lifecycle methods of class components and the hooks of functional components. It calls these methods and hooks at the appropriate times, ensuring that the components are updated correctly and efficiently.
Once the initial render phase is completed, React Fiber enters the commit phase, where it applies the changes to the DOM tree. This is done in a single pass to minimize the impact on the rendering performance.
React Fiber uses a tree data structure, known as the fiber tree, to represent the structure of a React application. Each node in the fiber tree, known as a fiber node, represents a React element and contains information about the element, such as its type, props, state, and relationships with other elements.
The fiber tree plays a crucial role in the rendering process in React Fiber. It is traversed to create units of work for each fiber node, and these units of work are then prioritized and performed based on their priority.
The fiber tree also plays a crucial role in the commit phase of React Fiber. During the commit phase, React Fiber traverses the fiber tree and applies the changes to the DOM tree. This is done in a single pass to minimize the impact on the rendering performance.
Incremental rendering is a key feature of React Fiber. It allows React to split rendering work into chunks and spread it out over multiple frames. This improves the responsiveness and renderability of user interfaces in React applications.
With incremental rendering, React can prioritize high-priority updates, such as user interactions and animation frames, over low-priority updates, such as offscreen rendering. This allows React to respond quickly to user interactions and maintain a smooth animation frame rate, even in complex and dynamic user interfaces.
Incremental rendering also provides a more predictable and controllable rendering environment. Developers can specify the priority of different updates and control when and how these updates are applied, making it easier to optimize the performance of React applications.
The call stack is a data structure used by JavaScript engines to keep track of function calls. When a function is called, a new stack frame is pushed onto the call stack. When a function returns, its stack frame is popped from the call stack.
In traditional JavaScript engines, the call stack is a "last in, first out" (LIFO) data structure. This means that the function that is currently being executed (i.e., the function at the top of the call stack) must finish executing before the next function can start.
However, this model can lead to problems in complex user interfaces, where many updates may need to be performed at the same time. If a low-priority update takes a long time to complete, it can block high-priority updates, leading to a poor user experience.
React Fiber solves this problem by introducing a new execution model based on a virtual stack frame. This model allows React to pause, resume, and reuse previously completed work, enabling incremental rendering and improving the responsiveness and renderability of user interfaces.
1 // An example of a long-running function that blocks the call stack 2 function longRunningFunction() { 3 let result = 0; 4 for (let i = 0; i < 1e9; i++) { 5 result += i; 6 } 7 return result; 8 } 9 10 // This function call will block the call stack until it finishes 11 longRunningFunction(); 12 13 // This function call will not start until the previous function finishes 14 console.log('Hello, world!'); 15
The DOM tree is a tree data structure that represents the structure of a web page. Each node in the DOM tree represents an HTML element and contains information about the element, such as its tag name, attributes, and child elements.
In React Fiber, the DOM tree is the final output of the rendering process. During the commit phase, React Fiber traverses the fiber tree and applies the changes to the DOM tree. This is done in a single pass to minimize the impact on the rendering performance.
React Fiber also uses the DOM tree to handle user interactions. When a user interacts with an element (e.g., by clicking a button or typing into an input field), React Fiber updates the corresponding fiber node and re-renders the affected parts of the DOM tree.
The current tree is a tree data structure that represents the current state of the user interface in a React application. It is one of the two trees that are compared during the reconciliation process, the other being the workinprogress tree.
During the render phase, React Fiber traverses the workinprogress tree and compares each fiber node with the corresponding fiber node in the current tree. If there are differences, React Fiber creates a unit of work for the fiber node and adds it to the update queue.
During the commit phase, React Fiber applies the updates to the DOM tree, transforming the current tree into the workinprogress tree. This process is known as "committing the work".
The current tree plays a crucial role in React Fiber. It allows React to keep track of the current state of the user interface and determine the minimum number of updates required to synchronize the user interface with the desired state.
The stack reconciler is the old reconciliation algorithm used by React before the introduction of React Fiber. It is called the "stack" reconciler because it uses the JavaScript call stack to keep track of the reconciliation process.
The stack reconciler works by traversing the component tree in a depth-first order and performing all the updates in a single pass. This approach is simple and efficient for small and static user interfaces, but it can lead to performance issues in complex and dynamic user interfaces.
React Fiber introduces a new reconciliation algorithm, known as the fiber reconciler, to address these issues. The fiber reconciler uses a virtual stack frame to enable incremental rendering, allowing React to split rendering work into chunks and spread it out over multiple frames. This improves the responsiveness and renderability of user interfaces in React applications.
The rendering process is a key part of React Fiber. It involves creating a fiber tree that mirrors the component tree of a React application, creating a unit of work for each fiber node, prioritizing and performing these units of work, and applying the changes to the DOM tree.
The rendering process in React Fiber works in two phases: the render phase and the commit phase. During the render phase, React Fiber traverses the workinprogress tree and creates a unit of work for each fiber node. These units of work are then prioritized and performed based on their priority.
During the commit phase, React Fiber applies the changes to the DOM tree. This is done in a single pass to minimize the impact on the rendering performance.
The rendering process also involves handling the lifecycle methods of class components and the hooks of functional components. React Fiber calls these methods and hooks at the appropriate times during the rendering process, ensuring that the components are updated correctly and efficiently.
1 // An example of a simple React component 2 function MyComponent() { 3 const [count, setCount] = React.useState(0); 4 5 return ( 6 <div> 7 <p>You clicked {count} times</p> 8 <button onClick={() => setCount(count + 1)}> 9 Click me 10 </button> 11 </div> 12 ); 13 } 14 15 // The rendering process in React Fiber 16 ReactDOM.render(<MyComponent />, document.getElementById('root')); 17
React Fiber is a powerful tool for building responsive and renderable user interfaces in React applications. It introduces a new reconciliation algorithm that enables incremental rendering, allowing React to split rendering work into chunks and spread it out over multiple frames.
React Fiber also provides a more predictable and controllable rendering environment. Developers can specify the priority of different updates and control when and how these updates are applied to the DOM tree. This makes it easier to optimize the performance of React applications.
Furthermore, React Fiber supports new features and improvements in the React ecosystem, such as the concurrent mode and the Suspense component. These features rely on the ability of React Fiber to pause, resume, and reuse previously completed work.
In conclusion, React Fiber is a significant advancement in the development of React applications. It improves the responsiveness and renderability of user interfaces, provides a more predictable and controllable rendering environment, and supports new features and improvements in the React ecosystem. Whether you're a seasoned React developer or just starting out, understanding and leveraging the power of React Fiber can help you build better React applications.
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