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

Array.prototype.entries() - JavaScript | MDN

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entries() 方法返回一个新的数组迭代器对象，该对象包含数组中每个索引的键/值对。

const array1 = ["a", "b", "c"];

const iterator1 = array1.entries();

console.log(iterator1.next().value);
// Expected output: Array [0, "a"]

console.log(iterator1.next().value);
// Expected output: Array [1, "b"]

一个新的可迭代迭代器对象。

当在稀疏数组上使用时，entries() 方法迭代空槽，就像它们的值为 undefined 一样。

entries() 方法是通用的。它只要求 this 值具有 length 属性和以整数为键的属性。

const a = ["a", "b", "c"];

for (const [index, element] of a.entries()) {
  console.log(index, element);
}

// 0 'a'
// 1 'b'
// 2 'c'

const array = ["a", "b", "c"];
const arrayEntries = array.entries();

for (const element of arrayEntries) {
  console.log(element);
}

// [0, 'a']
// [1, 'b']
// [2, 'c']

entries() 将访问空槽，就像它们是 undefined 一样。

for (const element of [, "a"].entries()) {
  console.log(element);
}
// [0, undefined]
// [1, 'a']

entries() 方法读取 this 的 length 属性，然后访问每个整数索引。

const arrayLike = {
  length: 3,
  0: "a",
  1: "b",
  2: "c",
};
for (const entry of Array.prototype.entries.call(arrayLike)) {
  console.log(entry);
}
// [ 0, 'a' ]
// [ 1, 'b' ]
// [ 2, 'c' ]

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