keys-iterator

Returns an iterator of the keys/indexes of an Object, Map, Array, or Typed Array. Useful for when you need the keys of a collection object but aren’t sure what type of collection you’ll be given.

Installation

Requires Node.js 6.0.0 or above.

npm i keys-iterator

API

The module exports a single function.

Parameters

1. Bindable: c (Array, iterator, Object, Map, Set, string, or Typed Array)
2. Object argument:
   • Optional: arrays / maps / sets (array, class, or string): A class that should be treated as equivalent to Array/Map/Set (respectively), the string name of such a class, or an array of such classes/strings.
   • Optional: inObj (boolean): Whether or not to act like the “in” operator by including inherited Object property keys. Only takes effect if c is an Object (i.e. not another recognized type). Defaults to false.
   • Optional: reflectObj (boolean): Whether or not to use reflection to include non-enumerable Object property keys. Only takes effect if c is an Object (i.e. not another recognized type). Defaults to false.

Return Value

An iterator which yields keys from the collection.

Examples

Arrays

const keys = require('keys-iterator')

const i = keys(['a', 'b'])
i.next().value // 0
i.next().value // 1
i.next().done // true

// Supports the bind operator
['a', 'b']::keys()

Iterators

keys-iterator will treat an iterator as if it were an array of values. Each “key” will be an incrementing integer index that starts at zero.

const keys = require('keys-iterator')

function * gen () {
  yield 'a'
  yield 'b'
}

const i = keys(gen())
i.next().value // 0
i.next().value // 1
i.next().done // true

Maps

const keys = require('keys-iterator')

const map = new Map()
map.set('key', 'value')

const i = keys(map)
i.next().value // 'key'
i.next().done // true

Objects

const keys = require('keys-iterator')

const i = keys({key: 'value'})
i.next().value // 'key'
i.next().done // true

// Supports the bind operator
const obj = {key: 'value'}
obj::keys()

Inherited Object Properties

Include Object property keys from the prototype chain by setting inObj to true:

const keys = require('keys-iterator')

function Cls () {}
Cls.prototype.key = 'value'

const i = keys(new Cls(), {inObj: true})
i.next().value // 'key'
i.next().done // true

Non-Enumerable Object Properties

Include non-enumerable Object property keys by setting reflectObj to true:

const keys = require('keys-iterator')

const obj = {}
Object.defineProperty(obj, 'key', {value: 'value', enumerable: false})

const i = keys(obj, {reflectObj: true})
i.next().value // 'key'
i.next().done // true

Sets

keys-iterator will treat a Set like an array, and will yield integer index keys starting at zero. Note that this behavior is different from that of the built-in Set.prototype.keys() method.

const keys = require('keys-iterator')

const set = new Set()
set.add('first')
set.add('second')

const i = keys(set)
i.next().value // 0
i.next().value // 1
i.next().done // true

Strings

keys-iterator will treat a string like a character array, and will yield integer index keys starting at zero.

const keys = require('keys-iterator')

const i = keys('hi')
i.next().value // 0
i.next().value // 1
i.next().done // true

Typed Arrays

const keys = require('keys-iterator')

const typedArray = new Int32Array(new ArrayBuffer(4))

const i = keys(typedArray)
i.next().value // 0
i.next().done // true

Related

• entries-iterator
• entries-array
• keys-array
• prop-keys
• values-iterator
• values-array