代理与反射：Proxy对象的实际应用场景

const createReactive = (obj, callback) => {

  return new Proxy(obj, {

    get(target, key) {

      return Reflect.get(target, key);

    },

    set(target, key, value) {

      const result = Reflect.set(target, key, value);

      callback(key, value); // 触发更新

      return result;

    }

  });

};

const state = createReactive({ count: 0 }, (key, val) => {

  console.log(`${key} changed to ${val}`);

});

state.count = 1; // 输出：count changed to 1

const createUser = (user) => {

  return new Proxy(user, {

    set(target, key, value) {

      if (key === 'email') {

        const emailRegex = /^[^\s@]+@[^\s@]+\.[^\s@]+$/;

        if (!emailRegex.test(value)) {

          throw new Error('Invalid email format');

        }

      }

      return Reflect.set(target, key, value);

    }

  });

};

const user = createUser({ name: 'Alice' });

user.email = 'alice@example.com'; // 成功

user.email = 'invalid'; // 抛错

const withLogging = (target) => {

  return new Proxy(target, {

    get(target, key) {

      const value = Reflect.get(target, key);

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      if (typeof value === 'function') {

        return function (...args) {

          console.log(`Calling ${key} with`, args);

          const start = performance.now();

          const result = value.apply(this, args);

          const end = performance.now();

          console.log(`${key} took ${end - start}ms`);

          return result;

        };

      }

      return value;

    }

  });

};

const api = withLogging({

  fetchUser(id) {

    return { id, name: 'Bob' };

  }

});

api.fetchUser(123);

const createSecureObject = (obj) => {

  return new Proxy(obj, {

    get(target, key) {

      if (key.startsWith('_')) {

        throw new Error(`Access denied to private property '${key}'`);

      }

      return Reflect.get(target, key);

    },

    set(target, key, value) {

      if (key.startsWith('_')) {

        throw new Error(`Cannot set private property '${key}'`);

      }

      return Reflect.set(target, key, value);

    }

  });

};

const inst = createSecureObject({ _secret: 'hide', name: 'Public' });

console.log(inst.name); // 正常输出

console.log(inst._secret); // 抛错