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WeakMap.prototype.has() - JavaScript | MDN

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WeakMap 实例的 has() 返回一个布尔值，指示该 WeakMap 中是否存在具有指定键的元素。

const weakmap1 = new WeakMap();
const object1 = {};
const object2 = {};

weakmap1.set(object1, "foo");

console.log(weakmap1.has(object1));
// Expected output: true

console.log(weakmap1.has(object2));
// Expected output: false

key

要测试是否在该 WeakMap 对象中存在的元素的键。

如果指定键的元素存在于 WeakMap 对象中，则返回 true；否则返回 false。如果 key 不是对象或非全局注册的符号，则始终返回 false。

const wm = new WeakMap();
wm.set(window, "foo");

wm.has(window); // 返回 true
wm.has("baz"); // 返回 false

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