🔑 fast-keys

fast-keys is a highly performant alternative to Object.keys. Its API has many of the same methods as Array.prototype, plus a few additional helpers.

• ⏩ 🏎 Really, really fast
• 🧠 Less heap allocation and garbage collection than Object.keys
• 🛠️ Extra utility methods

Why should I use this?

Object.keys has a significant performance cost. It's extremely common to use Object.keys to determine the number of keys in an object:

const object = { foo: 1, bar: 1, baz: 1 }
const keyLength = Object.keys(object).length

In order to determine the key length, the runtime will allocate an array containing all of the object's keys and then return the length of the array. For applications where performance is important, the cost of these array allocations quickly adds up. Not only is the array allocation expensive, the runtime will need to perform additional garbage collection to clean up the arrays.

Of course, it's possible to do explicit object key iteration in performance-critical applications - but by doing so we aren't able to use many of the useful functional tools available in the Javascript ecosystem.

This library provides the best of both worlds: the familiar functional-style Object.keys and Array.prototype interfaces without the performance costs of unnecessary Array allocations or garbage collection.

How fast is it?

It's about 8-10x faster than using Object.keys, depending on the properties of the objects and the Array.prototype methods. It also uses much less memory and requires less garbage collection, so the performance might be even better depending on your application.

Benchmarks

https://jsperf.com/fast-keys

Examples

import K from 'fast-keys'

const object = { foo: 1, bar: 1, baz: 1 }

console.log(K(object).length) // 3

console.log(K(object).map(string => string + '2')) // [ 'foo2', 'bar2', 'baz2' ]

console.log(K(object).toSet()) // Set { 'foo', 'bar', 'baz' }

fast-keys has many of the Array.prototype methods, and some extra helpers too.

API Reference

function K()

The default export of the module.

Accepts any non-nil value and returns a IFastKeys instance.

function K <ObjectType> (object: ObjectType): IFastKeys<ObjectType>

IFastKeys

The interface that exposes the Array.prototype methods.

interface IFastKeys <ObjectType> {
    length: number;

    some(iteratee: Predicate<ObjectType>): boolean
    map<A>(iteratee: (key: keyof ObjectType) => A): Array<A>
    toSet(): Set<keyof ObjectType>
    every(iteratee: Predicate<ObjectType>): boolean
    filter(iteratee: Predicate<ObjectType>): Array
    forEach(iteratee: (key: keyof ObjectType) => void): void
    find(predicate: Predicate<ObjectType>): keyof ObjectType | undefined
}

type Predicate <ObjectType> = (key: keyof ObjectType) => boolean

length	some()	map()	toSet()	every()	filter()	forEach()	find()

IFastKeys predicates are only passed the key and are not passed the index or the entire array of keys.

All functions only operate on keys that are own, enumerable, and string. This is the same behavior as Object.keys. Non-enumerable, inherited, and Symbol keys will be skipped.

IFastKeys instances don't cache or pre-compute the results of any calls, so you can use the same IFastKeys instance even if the underlying object changes. For example:

import K from 'fast-keys'

const object = { foo:1 }
const fkObject = K(object)

console.log(fkObject.length) // 1

object.bar = 1

console.log(fkObject.length) // 2

IFastKeys.length

^MDN The number of own (i.e. non-inherited) enumerable string keys of the object.

IFastKeys.some

^MDN Returns true if at least one key satisfies the predicate. Short-circuits and returns immediately if a key satisfies the predicate.

function some (iteratee: (key: string) => boolean): boolean

IFastKeys.map

^MDN Returns a new Array containing the results of applying the iteratee to each key in the object.

function map <A> (iteratee: (key: string) => A): Array<A>

IFastKeys.toSet

Returns a Set containing the object's keys. Equivalent to new Set(Object.keys(object)).

function toSet (): Set<string>

IFastKeys.every

^MDN Returns true if every key satisfies the predicate. Short-circuits and returns immediately if a key fails.

function every (iteratee: (key: string) => boolean): boolean

IFastKeys.filter

^MDN Returns a new Array containing only the keys that satisfy the predicate.

function filter (iteratee: (key: string) => boolean): Array<string>

IFastKeys.forEach

^MDN Execute some function for each key in the object. An opportunity to do side effects for each key.

function forEach (iteratee: (key: string) => void): void

IFastKeys.find

^MDN Returns the first key that satisfies the predicate, or returns undefined. Short-circuits and returns immediately if a matching key is found.

function find (iteratee: (key: string) => boolean): string | undefined