vue 响应式的数据原理

代码：
<!DOCTYPE html>
<html lang="en">
<head>
  <meta charset="UTF-8">
  <meta http-equiv="X-UA-Compatible" content="IE=edge">
  <meta name="viewport" content="width=device-width, initial-scale=1.0">
  <title>Document</title>
</head>
<body>
  <div id="app"></div>

  <script>
    let state = { count: 0 }; // 变成响应式的数据
    let active;

    function defineReactive(obj) {
      for (let key in obj) {
        let value = obj[key]; // 对象对应的值
        let dep = [];
        Object.defineProperty(obj, key, {
          get() {
            if (active) {
              dep.push(active); // 依赖收集
              return value;
            }
          },
          set(newValue) {
            // 触发更新
            value = newValue;
            dep.forEach((watcher) => watcher());
          },
        });
      }
    }

    defineReactive(state);

    const wacther = (fn) => {
      active = fn;
      fn(); // 调用函数
      active = null;
    };

    wacther(() => {
      app.innerHTML = state.count; // 取值
    });

    wacther(() => {
      console.log(state.count);
    });
  </script>
</body>
</html>