@dowhileluke/fns v2.0.1

fns

A collection of utility functions that I am too frequently copying between projects.

No dependencies, 60+ tests, tree-shakable, type-safe.

npm i @dowhileluke/fns

Array Methods

• categorize
• generateArray
• split
• sum
• tail
• truthy

Object Methods

• hasProp
• objectFilter
• objectFindKey
• objectMap

Array Methods

categorize

subdivide an array by some property of each element

const a = { age: 17 }
const b = { age: 40 }
const c = { age: 66 }

// Mode 1 -- boolean
const [babies, others] = categorize([a, b, c], x => x.age < 2)
// babies = []
// others = [a, b, c]

// Mode 2 -- category
function toCategory(person) {
	if (person.age < 2) return 'baby'
	if (person.age < 13) return 'child'
	if (person.age < 20) return 'teen'
	
	return 'adult'
}

const ageGroups = categorize([a, b, c] => toCategory)
// ageGroups.baby  = undefined
// ageGroups.child = undefined
// ageGroups.teen  = [a]
// ageGroups.adult = [b, c]
// Object.keys(ageGroups) = ['teen', 'adult']

generateArray

create a new array for a chosen number of elements or range of integer values

generateArray(4) // [0, 1, 2, 3]
generateArray(2, -2) // [2, 1, 0, -1, -2]

// optional argument: map function
generateArray(1, 3, n => null) // [null, null, null]

split

split an array (or string) in two at a given index

const [manyItems, finalTwo] = split([1, 2, 3, 4, 5], -2)
// manyItems = [1, 2, 3]
// finalTwo = [4, 5]

split('example', 2) // ['ex', 'ample']

sum

find the total of the given numbers

// Mode 1 -- simple
sum([1, 2, 3]) // 6

// Mode 2 -- element property
const cart = [
	{ price: 50, quantity: 2 },
	{ price: 20, quantity: 1 }
]

sum(cart, x => x.price * x.quantity) // 120

tail

get the last element

tail([5, 10, 15, 20]) // 20

truthy

filter a list to include only truthy elements

// Mode 1 -- array
truthy([0, 1, 2]) // [1, 2]

// Mode 2 -- arguments
const isRounded = false

truthy('box', isRounded && 'rounded') // ['box']

Object Methods

hasProp

check if an object contains a key

const example = { u: undefined }

hasProp(example, 'u') // true
hasProp(example, 'x') // false
hasProp('str', 'toLowerCase') // false, only exists on prototype

objectFilter

get a subset of an object (like Array#filter)

const directory = {
	101: { ownerId: 1 },
	102: { ownerId: 1 },
	103: { ownerId: 2 },
}

const ownedBy1 = objectFilter(directory, item => item.ownerId === 1)

Object.keys(ownedBy1) // ['101', '102']

objectFindKey

find an element in an object and return its key (like Array#findIndex)

const a = { value: 1 }
const b = { value: 2 }
const c = { value: 3 }

objectFindKey({ a, b, c }, x => x.value === 2) // 'b'

objectMap

convert each element in an object (like Array#map)

objectMap({ a: 1, b: 2, c: 3 }, x => x ** 2)
// { a: 1, b: 4, c: 9 }