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

Array.prototype.entries() - JavaScript | MDN

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Array 實例的 entries() 方法會回傳一個新的陣列迭代器物件，其中包含陣列中每個索引的鍵／值對。

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

const iterator1 = array1.entries();

console.log(iterator1.next().value);
// 預期輸出：Array [0, "a"]

console.log(iterator1.next().value);
// 預期輸出：Array [1, "b"]

無。

一個新的可迭代迭代器物件。

當 entries() 方法用於稀疏陣列時，它會將空槽視為 undefined 來進行迭代。

entries() 方法是通用的，它僅要求 this 物件具有 length 屬性及整數索引鍵屬性。

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() 方法會將空槽視為 undefined 來進行迭代。

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

entries() 方法會讀取 this 的 length 屬性，並存取所有鍵為非負整數且小於 length 的屬性。

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

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