浅析Vue2/Vue3中响应式的原理

<div id="app">
  <p>{{ message }}</p>
  <button @click="changeMessage">Change Message</button>
</div>
<script>
  const vm = new Vue({
    el: '#app',
    data: {
      message: 'Hello, Vue 2!'
    },
    methods: {
      changeMessage() {
        this.message = 'Hello, World!';
      }
    }
  });
</script>

// 简化版的观察者类
class SimpleWatcher {
  constructor(vm, key, updateFn) {
    this.vm = vm;
    this.key = key;
    this.updateFn = updateFn;
    // 在这里模拟一下Vue的依赖收集
    Dep.target = this;
    this.vm[this.key];
    Dep.target = null;
  }
  // 依赖更新时触发的方法
  update() {
    this.updateFn.call(this.vm, this.vm[this.key]);
  }
}
// 简化版的依赖管理类
class SimpleDep {
  constructor() {
    this.subscribers = [];
  }
  // 添加观察者
  addSubscriber(subscriber) {
    this.subscribers.push(subscriber);
  }
  // 通知观察者进行更新
  notify() {
    this.subscribers.forEach((subscriber) => subscriber.update());
  }
}
// 简化版的Vue响应式类
class SimpleVue {
  constructor(data) {
    this._data = data;
    this._proxyData(data);
  }
  // 将data对象转换为getter和setter
  _proxyData(data) {
    for (let key in data) {
      if (Object.prototype.hasOwnProperty.call(data, key)) {
        const dep = new SimpleDep();
        Object.defineProperty(data, key, {
          get: () => {
            if (Dep.target) {
              dep.addSubscriber(Dep.target);
            }
            return data['_'+key];
          },
          set: (newValue) => {
            data['_'+key] = newValue;
            dep.notify();
          },
        });
      }
    }
  }
}
// Dep类，用于简化依赖收集
class Dep {
  static target = null;
}

// 使用示例
const data = {
  message: 'Hello, Vue!'
};
const vm = new SimpleVue(data);
// 添加观察者
new SimpleWatcher(vm, 'message', (value) => {
  console.log('数据更新了：', value);
});
// 修改数据，触发更新
data.message = 'Hello, World!';

<div id="app">
  <p>{{ message }}</p>
  <button onclick="changeMessage()">Change Message</button>
</div>
<script>
  function reactive(data) {
    return new Proxy(data, {
      get(target, key) {
        console.log('读取数据', key);
        return target[key];
      },
      set(target, key, value) {
        console.log('更新数据', key, value);
        target[key] = value;
        updateView(); // 数据更新后，手动更新视图
        return true;
      }
    });
  }
  function updateView() {
    const messageElement = document.querySelector('p');
    messageElement.textContent = app.message;
  }
  const data = {
    message: 'Hello, Simple Vue!'
  };
  const app = reactive(data);
  function changeMessage() {
    app.message = 'Hello, World!';
  }
  // 页面加载完成后，手动更新视图
  updateView();
</script>