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WeakMap.prototype.has() - JavaScript | MDN
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WeakMap.prototype.has()
Baseline
Widely available
This feature is well established and works across many devices and browser versions. It’s been available across browsers since 2015年7月.
has() メソッドは、特定のキーをもつ要素が WeakMap オブジェクト内に存在するかどうかを示す真偽値を返します。
試してみましょう
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
構文
ws.has(key);
引数
key-
WeakMapオブジェクトに存在するかテストする要素のキーです。
返値
- Boolean
-
WeakMapオブジェクト内に特定のキーをもつ要素が存在していたらtrueを返します。さもなければfalseを返します。
例
has() メソッドの使用
js
var wm = new WeakMap();
wm.set(window, "foo");
wm.has(window); // true を返す
wm.has("baz"); // false を返す
仕様書
| Specification |
|---|
| ECMAScript® 2026 Language Specification # sec-weakmap.prototype.has |
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