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handler.ownKeys() - JavaScript | MDN

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handler.ownKeys() 方法用于拦截 Reflect.ownKeys().

const monster1 = {
  _age: 111,
  [Symbol("secret")]: "I am scared!",
  eyeCount: 4,
};

const handler1 = {
  ownKeys(target) {
    return Reflect.ownKeys(target);
  },
};

const proxy1 = new Proxy(monster1, handler1);

for (const key of Object.keys(proxy1)) {
  console.log(key);
  // Expected output: "_age"
  // Expected output: "eyeCount"
}

var p = new Proxy(target, {
  ownKeys: function (target) {},
});

下面的参数被传递给 ownKeys。this 被绑定在 handler 上。

target

目标对象。

ownKeys 方法必须返回一个可枚举对象。

handler.ownKeys() 方法用于拦截 Reflect.ownKeys().

如果违反了下面的约束，proxy 将抛出错误 TypeError:

• ownKeys 的结果必须是一个数组。
• 数组的元素类型要么是一个 String ，要么是一个 Symbol.
• 结果列表必须包含目标对象的所有不可配置（non-configurable）、自有（own）属性的 key.
• 如果目标对象不可扩展，那么结果列表必须包含目标对象的所有自有（own）属性的 key，不能有其他值。

下面的代码拦截 Object.getOwnPropertyNames().

var p = new Proxy(
  {},
  {
    ownKeys: function (target) {
      console.log("called");
      return ["a", "b", "c"];
    },
  },
);

console.log(Object.getOwnPropertyNames(p)); // "called"; outputs [ 'a', 'b', 'c' ]

下面的代码违反了约定

var obj = {};
Object.defineProperty(obj, "a", {
  configurable: false,
  enumerable: true,
  value: 10,
});

var p = new Proxy(obj, {
  ownKeys: function (target) {
    return [123, 12.5, true, false, undefined, null, {}, []];
  },
});

console.log(Object.getOwnPropertyNames(p));

// TypeError: proxy [[OwnPropertyKeys]] 必须返回一个数组
// 数组元素类型只能是 String 或 Symbol

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