Array.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 May 2018.

keys() 方法返回一个新的数组迭代器对象,其中包含数组中每个索引的键。

尝试一下

const array1 = ["a", "b", "c"];
const iterator = array1.keys();

for (const key of iterator) {
  console.log(key);
}

// Expected output: 0
// Expected output: 1
// Expected output: 2

语法

js
keys()

返回值

描述

当用于稀疏数组时,keys() 方法迭代空槽,就像它们的值为 undefined 一样。

keys() 方法是通用的。它只期望 this 值具有 length 属性和整数键属性。

示例

在稀疏数组中使用 keys()

Object.keys() 只包含数组中实际存在的键不同,keys() 迭代器不会忽略缺失属性的键。

js
const arr = ["a", , "c"];
const sparseKeys = Object.keys(arr);
const denseKeys = [...arr.keys()];
console.log(sparseKeys); // ['0', '2']
console.log(denseKeys); // [0, 1, 2]

在非数组对象上调用 keys()

keys() 方法读取 thislength 属性,然后生成 0 到 length - 1 之间的所有整数索引。实际并不会访问索引。

js
const arrayLike = {
  length: 3,
};
for (const entry of Array.prototype.keys.call(arrayLike)) {
  console.log(entry);
}
// 0
// 1
// 2

规范

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

浏览器兼容性

Report problems with this compatibility data on GitHub
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

参见