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

Map.prototype.has() - JavaScript | MDN

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Map 实例的 has() 方法返回一个布尔值，指示具有指定键的元素是否存在。

const map1 = new Map();
map1.set("bar", "foo");

console.log(map1.has("bar"));
// Expected output: true

console.log(map1.has("baz"));
// Expected output: false

key

用于测试 Map 对象中是否存在的元素的键。

如果 Map 对象中存在具有指定键的元素，则返回 true；否则返回 false。

const myMap = new Map();
myMap.set("bar", "foo");

console.log(myMap.has("bar")); // true
console.log(myMap.has("baz")); // false

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