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实现简易react

2026-01-26 12:13:47React

实现简易 React 的核心要素

要实现一个简易 React，需要模拟其核心功能：虚拟 DOM、组件化、状态管理和渲染机制。以下是关键步骤和代码示例。

虚拟 DOM 结构

虚拟 DOM 是真实 DOM 的轻量级表示，通常是一个 JavaScript 对象。定义一个简单的虚拟 DOM 结构：

function createElement(type, props, ...children) {
  return {
    type,
    props: {
      ...props,
      children: children.map(child =>
        typeof child === 'object' ? child : createTextElement(child)
      ),
    },
  };
}

function createTextElement(text) {
  return {
    type: 'TEXT_ELEMENT',
    props: {
      nodeValue: text,
      children: [],
    },
  };
}

渲染函数

将虚拟 DOM 渲染到真实 DOM 中。递归处理虚拟 DOM 节点并创建对应的真实 DOM 节点：

function render(element, container) {
  const dom =
    element.type === 'TEXT_ELEMENT'
      ? document.createTextNode('')
      : document.createElement(element.type);

  const isProperty = key => key !== 'children';
  Object.keys(element.props)
    .filter(isProperty)
    .forEach(name => {
      dom[name] = element.props[name];
    });

  element.props.children.forEach(child =>
    render(child, dom)
  );

  container.appendChild(dom);
}

组件和状态管理

实现一个简单的函数组件和状态管理机制。使用闭包和钩子模拟 useState：

let currentHook = null;
let hookIndex = 0;
let componentInstance = null;

function useState(initialState) {
  const hooks = componentInstance.hooks;
  const existingHook = hooks[hookIndex];
  const hook = {
    state: existingHook ? existingHook.state : initialState,
    queue: [],
  };

  const actions = existingHook ? existingHook.queue : [];
  actions.forEach(action => {
    hook.state = typeof action === 'function' ? action(hook.state) : action;
  });

  const setState = action => {
    hook.queue.push(action);
    // 触发重新渲染
    render(componentInstance.element, componentInstance.container);
  };

  hooks[hookIndex] = hook;
  hookIndex++;
  return [hook.state, setState];
}

function createComponent(fn, props) {
  return {
    fn,
    props,
    hooks: [],
    element: null,
    container: null,
  };
}

示例使用

将上述功能组合起来，实现一个简单的计数器组件：

function Counter() {
  const [count, setCount] = useState(0);

  return createElement('div', null,
    createElement('h1', null, 'Count: ', count),
    createElement('button', { onClick: () => setCount(c => c + 1) }, 'Increment')
  );
}

const container = document.getElementById('root');
const element = createElement(Counter, null);
componentInstance = createComponent(Counter, null);
componentInstance.element = element;
componentInstance.container = container;
render(element, container);