Array.prototype.entries()

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"]

entries()

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']

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

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' ]