Array.prototype.entries()

¥Syntax

entries()

¥Parameters

没有任何。

¥None.

¥Return value

新的 可迭代的迭代器对象。

¥A new iterable iterator object.

¥Description

当在 稀疏数组 上使用时，entries() 方法会迭代空槽，就好像它们具有值 undefined 一样。

¥When used on sparse arrays, the entries() method iterates empty slots as if they have the value undefined.

entries() 方法是 generic。它只期望 this 值具有 length 属性和整数键控属性。

¥The entries() method is generic. It only expects the this value to have a length property and integer-keyed properties.

¥Examples

¥Iterating with index and element

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

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

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

¥Using a for...of loop

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

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

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

¥Iterating sparse arrays

entries() 将像 undefined 一样访问空槽。

¥entries() will visit empty slots as if they are undefined.

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

¥Calling entries() on non-array objects

entries() 方法读取 this 的 length 属性，然后访问键为小于 length 的非负整数的每个属性。

¥The entries() method reads the length property of this and then accesses each property whose key is a nonnegative integer less than length.

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

¥See also

• core-js 中 Array.prototype.entries 的 Polyfill
• 索引集合 指南
• Array
• Array.prototype.keys()
• Array.prototype.values()
• Array.prototype[Symbol.iterator]()
• TypedArray.prototype.entries()
• 迭代协议