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  1. 給開發者的 Web 技術文件
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  3. JavaScript 參考文件
  4. 標準內建物件
  5. Array
  6. Array.prototype.keys()
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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 2015年7月.

keys() 方法會回傳一個包含陣列中的每一個索引之鍵（keys）的新 Array Iterator 物件。

In this article

嘗試一下

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

語法

arr.keys()

回傳值

一個新的 Array 迭代器（iterator）物件。

範例

鍵迭代器不會乎略陣列中的空元素

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

規範

Specification
ECMAScript® 2027 Language Specification
# sec-array.prototype.keys

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  1. 標準內建物件
  2. Array
  3. 建構子
    1. Array()
  4. 靜態方法
    1. Array.from()
    2. fromAsync()
    3. Array.isArray()
    4. Array.of()
  5. 靜態屬性
    1. [Symbol.species]
  6. 實體方法
    1. at()
    2. Array.prototype.concat()
    3. Array.prototype.copyWithin()
    4. Array.prototype.entries()
    5. every()
    6. Array.prototype.fill()
    7. Array.prototype.filter()
    8. Array.prototype.find()
    9. Array.prototype.findIndex()
    10. findLast()
    11. findLastIndex()
    12. Array.prototype.flat()
    13. flatMap()
    14. forEach()
    15. Array.prototype.includes()
    16. Array.prototype.indexOf()
    17. Array.prototype.join()
    18. Array.prototype.keys()
    19. Array.prototype.lastIndexOf()
    20. Array.prototype.map()
    21. Array.prototype.pop()
    22. Array.prototype.push()
    23. Array.prototype.reduce()
    24. reduceRight()
    25. Array.prototype.reverse()
    26. Array.prototype.shift()
    27. Array.prototype.slice()
    28. some()
    29. Array.prototype.sort()
    30. Array.prototype.splice()
    31. toLocaleString()
    32. toReversed()
    33. toSorted()
    34. toSpliced()
    35. Array.prototype.toString()
    36. Array.prototype.unshift()
    37. Array.prototype.values()
    38. with()
    39. Array.prototype[Symbol.iterator]()
  7. 實體屬性
    1. Array.length
    2. [Symbol.unscopables]
  8. 繼承
  9. Object/Function
  10. 靜態方法
    1. Function.prototype.apply()
    2. Function.prototype.bind()
    3. Function.prototype.call
    4. toString()
    5. [Symbol.hasInstance]()
  11. 靜態屬性
    1. displayName
    2. Function.length
    3. name
    4. prototype
    5. arguments
    6. caller
  12. 實體方法
    1. __defineGetter__()
    2. __defineSetter__()
    3. __lookupGetter__()
    4. __lookupSetter__()
    5. Object.prototype.hasOwnProperty()
    6. isPrototypeOf()
    7. propertyIsEnumerable()
    8. toLocaleString()
    9. toString()
    10. valueOf()
  13. 實體屬性
    1. __proto__
    2. constructor

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