深入了解 React Fiber：应用与源码实现

import React, { useState, useEffect } from 'react';

const ExampleComponent = ({ count }) => {
  const [value, setValue] = useState(0);

  useEffect(() => {
    const fetchData = async () => {
      try {
        await new Promise(resolve => setTimeout(resolve, 1000));
        setValue(count);
      } catch (error) {
        console.error('Error fetching data:', error);
      }
    };

    fetchData();
  }, [count]);

  return (
    <div>
      <p>Value: {value}</p>
    </div>
  );
};

const ParentComponent = () => {
  const [count, setCount] = useState(0);

  const handleClick = () => {
    setCount(prevCount => prevCount + 1);
  };

  return (
    <div>
      <button onClick={handleClick}>Increment Count</button>
      <ExampleComponent count={count} />
    </div>
  );
};

export default ParentComponent;
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import React, { memo } from 'react';

const MemoizedComponent = memo(({ data }) => {
  // 仅在 data 发生变化时重新渲染
  return <div>Data: {data}</div>;
});
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// 定义 React Fiber 节点的数据结构
class FiberNode {
  constructor(tag, props, key) {
    this.tag = tag; // 组件类型（函数组件、类组件、原生组件等）
    this.props = props; // 组件的属性
    this.key = key; // 组件的 key
    this.child = null; // 第一个子节点
    this.sibling = null; // 兄弟节点
    this.return = null; // 父节点
    this.effectTag = null; // 标记节点需要进行的操作（更新、插入、删除等）
  }
}

// 任务类型
const HostRoot = 3; // 根节点
const HostComponent = 5; // 原生组件

// 工作单元
let nextUnitOfWork = null;

// 创建 Fiber 节点
function createFiber(tag, props, key) {
  return new FiberNode(tag, props, key);
}

// 构建 Fiber 树
function reconcileChildren(workInProgress, children) {
  let prevFiber = null;
  let oldFiber = workInProgress.alternate && workInProgress.alternate.child;

  for (let i = 0; i < children.length || oldFiber !== null; i++) {
    const child = children[i];
    let newFiber = null;

    const sameType = oldFiber && child && child.type === oldFiber.type;

    if (sameType) {
      // 类型相同，复用旧 Fiber 节点
      newFiber = createFiber(child.type, child.props, child.key);
      newFiber.alternate = oldFiber;
      newFiber.return = workInProgress;
      newFiber.effectTag = 'UPDATE';
    }

    if (!sameType && child) {
      // 类型不同，创建新的 Fiber 节点
      newFiber = createFiber(child.type, child.props, child.key);
      newFiber.return = workInProgress;
      newFiber.effectTag = 'PLACEMENT';
    }

    if (!sameType && oldFiber) {
      // 类型不同，删除旧的 Fiber 节点
      oldFiber.effectTag = 'DELETION';
      workInProgress.effectTag = 'UPDATE';
    }

    if (oldFiber) {
      oldFiber = oldFiber.sibling;
    }

    if (i === 0) {
      workInProgress.child = newFiber;
    } else if (prevFiber) {
      prevFiber.sibling = newFiber;
    }

    prevFiber = newFiber;
  }
}

// 创建任务
function performUnitOfWork(workInProgress) {
  // 处理当前任务
  const { type, props } = workInProgress;
  if (typeof type === 'string') {
    // 原生组件
    updateHostComponent(workInProgress);
  } else if (

typeof type === 'function') {
    // 函数组件
    updateFunctionComponent(workInProgress);
  }

  // 返回下一个任务
  if (workInProgress.child) {
    return workInProgress.child;
  }

  let nextFiber = workInProgress;
  while (nextFiber) {
    if (nextFiber.sibling) {
      return nextFiber.sibling;
    }
    nextFiber = nextFiber.return;
  }

  return null;
}

// 更新原生组件
function updateHostComponent(workInProgress) {
  // 简化版本，不处理属性更新等逻辑
  if (!workInProgress.stateNode) {
    workInProgress.stateNode = document.createElement(workInProgress.type);
  }

  reconcileChildren(workInProgress, workInProgress.props.children);
}

// 更新函数组件
function updateFunctionComponent(workInProgress) {
  // 简化版本，不处理 Hook 等逻辑
  const children = workInProgress.type(workInProgress.props);
  reconcileChildren(workInProgress, children);
}

// 开始渲染
function render(element, container) {
  const rootFiber = createFiber(HostRoot, { children: [element] });
  nextUnitOfWork = rootFiber;
}

// 工作循环
function workLoop(deadline) {
  while (nextUnitOfWork && deadline.timeRemaining() > 1) {
    nextUnitOfWork = performUnitOfWork(nextUnitOfWork);
  }

  if (!nextUnitOfWork) {
    console.log('Render complete');
  }

  requestIdleCallback(workLoop);
}

// 启动渲染
requestIdleCallback(workLoop);

// 示例应用
const element = <div>Hello, Fiber!</div>;
const container = document.getElementById('root');
render(element, container);
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