Map.prototype.keys()

Baseline Widely available

This feature is well established and works across many devices and browser versions. It’s been available across browsers since July 2015.

keys()Map インスタンスのメソッドで、この Map オブジェクトに挿入された要素のキーを挿入順に列挙する新しいイテレーターオブジェクトを返します。

試してみましょう

const map1 = new Map();

map1.set("0", "foo");
map1.set(1, "bar");

const iterator1 = map1.keys();

console.log(iterator1.next().value);
// Expected output: "0"

console.log(iterator1.next().value);
// Expected output: 1

構文

js
keys()

引数

なし。

返値

keys() の使用

js
const myMap = new Map();
myMap.set("0", "foo");
myMap.set(1, "bar");
myMap.set({}, "baz");

const mapIter = myMap.keys();

console.log(mapIter.next().value); // "0"
console.log(mapIter.next().value); // 1
console.log(mapIter.next().value); // {}

仕様書

Specification
ECMAScript® 2025 Language Specification
# sec-map.prototype.keys

ブラウザーの互換性

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desktopmobileserver
Chrome
Edge
Firefox
Opera
Safari
Chrome Android
Firefox for Android
Opera Android
Safari on iOS
Samsung Internet
WebView Android
WebView on iOS
Deno
Node.js
keys

Legend

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Full support
Full support

関連情報