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Showing content from https://developer.mozilla.org/zh-CN/docs/Web/JavaScript/Reference/Global_Objects/WeakSet/has below:

WeakSet.prototype.has() - JavaScript | MDN

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WeakSet 实例的 has() 方法返回一个布尔值，指示该 WeakSet 中指定的对象是否存在。

const weakset1 = new WeakSet();
const object1 = {};
const object2 = {};

weakset1.add(object1);

console.log(weakset1.has(object1));
// Expected output: true

console.log(weakset1.has(object2));
// Expected output: false

value

要测试是否在该 WeakSet 对象中存在的值。

如果指定的值存在于 WeakSet 对象中，则返回 true；否则返回 false。如果 value 不是对象或非全局注册的符号，则始终返回 false。

const ws = new WeakSet();
const obj = {};
ws.add(window);

ws.has(window); // 返回 true
ws.has(obj); // 返回 false

// 存储非全局注册的符号
const sym = Symbol("foo");
ws.add(sym);
ws.add(Symbol.iterator);

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