Array.prototype.keys()

The keys() method returns a new Array Iterator object that contains the keys for each index in the array.

Syntax

arr.keys()

Return value

A new Array iterator object.

Examples

Key iterator doesn't ignore holes

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

Specifications

Specification
ECMAScript (ECMA-262)
The definition of 'Array.prototype.keys' in that specification.

Browser compatibility

Update compatibility data on GitHub
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ChromeEdgeFirefoxInternet ExplorerOperaSafariAndroid webviewChrome for AndroidFirefox for AndroidOpera for AndroidSafari on iOSSamsung InternetNode.js
keysChrome Full support 38Edge Full support 12Firefox Full support 28IE No support NoOpera Full support 25Safari Full support 8WebView Android Full support 38Chrome Android Full support 38Firefox Android Full support 28Opera Android Full support 25Safari iOS Full support 8Samsung Internet Android Full support 3.0nodejs Full support 0.12

Legend

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See also

Related Topics
  1. Standard built-in objects
  2. Array
  3. Properties
    1. Array.length
    2. Array.prototype[@@unscopables]
  4. Methods
    1. Array.from()
    2. Array.isArray()
    3. Array.observe()
    4. Array.of()
    5. Array.prototype.concat()
    6. Array.prototype.copyWithin()
    7. Array.prototype.entries()
    8. Array.prototype.every()
    9. Array.prototype.fill()
    10. Array.prototype.filter()
    11. Array.prototype.find()
    12. Array.prototype.findIndex()
    13. Array.prototype.flat()
    14. Array.prototype.flatMap()
    15. Array.prototype.forEach()
    16. Array.prototype.includes()
    17. Array.prototype.indexOf()
    18. Array.prototype.join()
    19. Array.prototype.keys()
    20. Array.prototype.lastIndexOf()
    21. Array.prototype.map()
    22. Array.prototype.pop()
    23. Array.prototype.push()
    24. Array.prototype.reduce()
    25. Array.prototype.reduceRight()
    26. Array.prototype.reverse()
    27. Array.prototype.shift()
    28. Array.prototype.slice()
    29. Array.prototype.some()
    30. Array.prototype.sort()
    31. Array.prototype.splice()
    32. Array.prototype.toLocaleString()
    33. Array.prototype.toSource()
    34. Array.prototype.toString()
    35. Array.prototype.unshift()
    36. Array.prototype.values()
    37. Array.prototype[@@iterator]()
    38. Array.unobserve()
    39. get Array[@@species]
  5. Inheritance:
  6. Function
  7. Properties
    1. Function.arguments
    2. Function.arity
    3. Function.caller
    4. Function.displayName
    5. Function.length
    6. Function.name
  8. Methods
    1. Function.prototype.apply()
    2. Function.prototype.bind()
    3. Function.prototype.call()
    4. Function.prototype.isGenerator()
    5. Function.prototype.toSource()
    6. Function.prototype.toString()
  9. Object
  10. Properties
    1. Object.prototype.__count__
    2. Object.prototype.__noSuchMethod__
    3. Object.prototype.__parent__
    4. Object.prototype.__proto__
    5. Object.prototype.constructor
  11. Methods
    1. Object.prototype.__defineGetter__()
    2. Object.prototype.__defineSetter__()
    3. Object.prototype.__lookupGetter__()
    4. Object.prototype.__lookupSetter__()
    5. Object.prototype.hasOwnProperty()
    6. Object.prototype.isPrototypeOf()
    7. Object.prototype.propertyIsEnumerable()
    8. Object.prototype.toLocaleString()
    9. Object.prototype.toSource()
    10. Object.prototype.toString()
    11. Object.prototype.unwatch()
    12. Object.prototype.valueOf()
    13. Object.prototype.watch()
    14. Object.setPrototypeOf()