A collection of common, sometimes functional utilities. Uses fast.js + katsu-curry
sort, keys, freeze, assign, and lengthallot, and the partially applied forms grab and takepath, pathOr, prop, and propOrmerge, pathIs, pathEq, propIs, propEq and equalskatsu-curry, whose public API changedchaininvert, not, not1, not2, not3 and updated documentationtoPairs / entries and fromPairsap, foldisDistinctObjectrange, speed improvementsap spec, added bunch of string prototype methods, and added dont-break for better safety in future upgradesApply a list of functions to a list of values
Parameters
applicative (function | Array<functions>) a single function or array of applicativesfunctor Array an array of valuesExamples
import {ap} from 'f-utility'
ap([
(x) => x.toUppercase(),
(x) => `${x} batteries`
],
`abc`.split(``)
) // [`A`, `B`, `C`, `a batteries`, `b batteries`, `c batteries`]
Returns Array a concatenated list of all applicatives applied to all values
string.prototype.join but curried
Parameters
Examples
import {join} from 'f-utility'
join(`x`, [1,2,3]) // `1x2x3`
Returns string joined
return a new array with some other stuff added to it
Parameters
Returns Array combined array
string.prototype.sort but curried
Parameters
Examples
import {sort} from 'f-utility'
sort((x) => x % 2, [1,2,3,4,5,6,7,8]) // [ 0, 2, 4, 6, 8, 9, 7, 5, 3, 1 ]
Returns Array sorted
get the difference between two arrays
Parameters
Examples
import {difference} from 'f-utility'
difference([1,2,3], [2,4,6]) // [4, 6]
difference([2,4,6], [1,2,3]) // [1, 3]
Returns Array filtered array with differences between the two arrays
get both the differences between two arrays, and if one difference is longer, return it
Parameters
Examples
import {symmetricDifference} from 'f-utility'
difference([1,2,3], [1,2]) // [3]
Returns Array filtered array with differences between the two arrays
alter the index of a given array input
Parameters
index number the index to alterfn Function the function to describe the alterationinput Array the input arrayExamples
import {alterIndex} from 'f-utility'
const input = `abcde`.split(``)
alterIndex(0, () => `butts`, input) // [`butts`, `b`, `c`, `d`, `e`]
// also works with negative indicies
alterIndex(-1, () => `x`, input) // [`a`, `b`, `c`, `d`, `x`]
Returns Array an altered copy of the original array
functor.chain(fn) but curried and fast
Parameters
Examples
import {chain} from 'f-utility'
const split = (x) => x.split(``)
const flatSplit = chain(split)
const a = flatSplit([`chain`, `is`, `flatMap`])
console.log(a) // [ 'c', 'h', 'a', 'i', 'n', 'i', 's', 'f', 'l', 'a', 't', 'M', 'a', 'p' ]
Returns (Array | Monad) flat mapped iterable
takes a function that takes two parameters and returns a ternary result
Parameters
cnFn functiona any anythingb any anythingExamples
import {choice} from 'f-utility'
const max = choice((a, b) => a > b)
max(500, 20) // 500
max(20, 500) // 500
Returns any result
a delegatee last function for Either.fold ing
Parameters
Examples
import {I, I, pipe, fold} from 'f-utility'
import {Left, Right} from 'fantasy-eithers'
const saferDivide = (a, b) => (b !== 0 ? Right(a / b) : Left(`Cannot divide by zero`))
fold(I, I, saferDivide(1, 2)) // 0.5
fold(I, I, saferDivide(1, 0)) // `Cannot divide by zero`
Returns any the result of the fold
array.filter(fn) but inverted order, curried and fast
Parameters
Examples
import {filter} from 'f-utility'
filter((x) => x % 2 === 0, [1,2,3,4,5,6,7,8]) // [2,4,6,8]
Returns Array filtered iterable
take a function, flip the two parameters being passed to it, curry it
Parameters
fn function a functionExamples
import {flip} from 'f-utility'
const divide = (a, b) => a / b
const ivideday = flip(divide)
divide(1, 5) // 0.2
ivideday(1, 5) // 5
Returns any the result of invoking function with two inverted parameters
a delegatee last function for Future.fork ing
Parameters
Examples
import {pipe, fork, I} from 'f-utility'
import {trace} from 'xtrace'
import F from 'fluture'
const odd = (x) => (x % 2 === 0 ? F.of(x) : F.reject(`${x} is odd`))
const semiSafeOddity = pipe(
odd,
trace(`oddity`),
fork(console.warn, console.log)
)
semiSafeOddity(5) // console.warn(`5 is odd`)
semiSafeOddity(4) // console.log(4)
Returns any the result of the fork
Parameters
x any anyExamples
import {pipe, invert} from 'f-utility'
const isOdd = pipe(
(x) => x % 2 === 0,
invert
)
Returns boolean !x
return the result of inverting a nullary function
Parameters
fn function a function to invert the result ofExamples
import {not, equal} from 'f-utility'
const ID = 12345
const isntID = not(equal(ID))
isntID(ID) // false
isntID(123) // true
Returns function function
return the result of inverting a unary function
Parameters
fn function a function to invert the result ofa any a parameter to pass to the functionExamples
import {not, equal} from 'f-utility'
const ID = 12345
const isntID = not1(equal, ID)
isntID(ID) // false
isntID(123) // true
Returns function inverted function
return the result of inverting a binary function
Parameters
fn function a function to invert the result ofa any a parameter to pass to the functionb any a parameter to pass to the functionReturns function inverted function
return the result of inverting a tertiary function
Parameters
fn function a function to invert the result ofa any a parameter to pass to the functionb any a parameter to pass to the functionc any a parameter to pass to the functionReturns function inverted function
call a function x times and aggregate the result
Parameters
Examples
import {iterate} from 'f-utility'
iterate(5, () => `x`) // [`x`, `x`, `x`, `x`, `x`]
Returns Array aggregated values from invoking a given function
functor.map(fn) but curried and fast (though will delegate to the functor)
Parameters
Examples
import {map} from 'f-utility'
const add1 = map((x) => x + 1)
add1([1,2,3]) // [2,3,4]
Returns Array mapped iterable
=== comparison
Parameters
a any anythingb any anythingExamples
import {equals} from 'f-utility'
const SAFE_ID = 123456
const equalsID = equals(SAFE_ID)
equalsID(200) // false
equalsID(SAFE_ID) // true
Returns boolean whether a triple-equals b
comparison but inverted
Parameters
b any anythinga any anythingExamples
import {greaterThan, gt} from 'f-utility'
gt(100, 99) // false
gt(100, 100) // false
gt(100, 101) // true
Returns boolean whether a > b
= comparison but inverted
Parameters
b any anythinga any anythingExamples
import {greaterThanOrEqualTo, gte} from 'f-utility'
gte(100, 99) // false
gte(100, 100) // true
gte(100, 101) // true
Returns boolean whether a > b
< comparison but inverted
Parameters
b any anythinga any anythingExamples
import {lessThan, lt} from 'f-utility'
lt(100, 99) // true
lt(100, 100) // false
lt(100, 101) // false
Returns boolean whether a > b
< comparison but inverted
Parameters
b any anythinga any anythingExamples
import {lessThanOrEqualTo, lte} from 'f-utility'
lte(100, 99) // true
lte(100, 100) // true
lte(100, 101) // false
Returns boolean whether a > b
convenience method for Math.round
Parameters
x number a numberExamples
import {round} from 'f-utility'
round(10.3) // 10
round(10.9) // 11
Returns number rounded number
add things
Parameters
Examples
import {add} from 'f-utility'
add(4, 2) // 6
Returns number sum
subtract things
Parameters
Examples
import {subtract} from 'f-utility'
subtract(4, 2) // -2
Returns number subtracted
multiply things
Parameters
Examples
import {multiply} from 'f-utility'
multiply(4, 2) // 8
Returns number multiplied
divide things
Parameters
Examples
import {divide} from 'f-utility'
divide(4, 2) // 0.5
Returns number divided
exponentiate things
Parameters
Examples
import {pow} from 'f-utility'
pow(4, 2) // 16
Returns number b to the power of a
Object.keys https://developer.mozilla.org/en-US/docs/Web/JavaScript/Reference/Global_Objects/Object/keys
Parameters
a Object an objectExamples
import {keys} from 'f-utility'
keys({a: 1, b: 2}) // [`a`, `b`]
Returns Array an array of keys
Parameters
x Object inputExamples
import {values} from 'f-utility'
values({a:1, b: 2, c: 3}) // [1, 2, 3]
Returns Array<Strings> values - an array of properties
Object.freeze https://developer.mozilla.org/en-US/docs/Web/JavaScript/Reference/Global_Objects/Object/freeze
Parameters
a Object an objectExamples
import {freeze} from 'f-utility'
const immutable = freeze({a: 1, b: 2})
immutable.a = 5 // throws error
Returns Object a frozen object
Object.assign https://developer.mozilla.org/en-US/docs/Web/JavaScript/Reference/Global_Objects/Object/assign
Parameters
a Object any number of objectsExamples
import {assign} from 'f-utility'
assign({c: 3}, {a: 1, b: 2}) // {a: 1, b: 2, c: 3}
Returns Object a merged object
object.assign but enforced as a binary function
Parameters
Examples
import {merge} from 'f-utility'
merge({c: 3}, {a: 1, b: 2}) // {a: 1, b: 2, c: 3}
Returns Object c - the results of merging a and b
Object.entries shim https://developer.mozilla.org/en-US/docs/Web/JavaScript/Reference/Global_Objects/Object/entries
Parameters
o Object an objectExamples
import {entries} from 'f-utility'
entries({a: 1, b: 2}) // [[`a`, 1], [`b`, 2]]
Returns Array an array of tuples [key, value] pairs
An alias of entries
https://developer.mozilla.org/en-US/docs/Web/JavaScript/Reference/Global_Objects/Object/entries
Parameters
o Object an objectExamples
import {toPairs} from 'f-utility'
toPairs({a: 1, b: 2}) // [[`a`, 1], [`b`, 2]]
Returns Array an array of tuples [key, value] pairs
convert a list of key value pairs into an object
Parameters
null-null Array a list of [key, value] pairsExamples
import {fromPairs} from 'f-utility'
fromPairs([[`a`, 1], [`b`, 2]]) // {a: 1, b: 2}
Returns Object merged results
a simple object tuple-mapper
Parameters
Examples
import {mapTuples} from 'f-utility'
const input = {
a: 1,
b: 2,
c: 3
}
const fn = ([k, v]) => ([k.toUpperCase(), v * 2])
mapTuples(fn, input) // {A: 2, B: 4, C: 6}
Returns Object a mapped object
a simple object value-only tuple-mapper
Parameters
Examples
import {mapValues} from 'f-utility'
const input = {
a: 1,
b: 2,
c: 3
}
const fn = (v) => (v * 2)
mapValues(fn, input) // {a: 2, b: 4, c: 6}
Returns Object a mapped object
a simple object key-only tuple-mapper
Parameters
Examples
import {mapKeys} from 'f-utility'
const input = {
a: 1,
b: 2,
c: 3
}
const fn = (v) => `__${v}`
mapKeys(fn, input) // {__a: 1, __b: 2, __c: 3}
Returns Object a mapped object
Grab a nested value from an object or return a default
Parameters
def any a default valuelenses Array<string> a list of nested propertiesinput any an object to grab things fromExamples
import {pathOr} from 'f-utility'
pathOr(`default`, [`a`, `b`, `c`], {a: {b: {c: `actual`}}}) // `actual`
pathOr(`default`, [`a`, `b`, `c`], {x: {y: {z: `actual`}}}) // `default`
Returns any a nested value or default
Grab a nested value from an object
Parameters
Examples
import {path} from 'f-utility'
pathOr([`a`, `b`, `c`], {a: {b: {c: `actual`}}}) // `actual`
pathOr([`a`, `b`, `c`], {x: {y: {z: `actual`}}}) // null
Returns any a nested value or null
Grab a property from an object or return a default
Parameters
def any a default valueproperty string a propertyinput any an object to grab things fromExamples
import {propOr} from 'f-utility'
pathOr(`default`, `c`, {c: `actual`}) // `actual`
pathOr(`default`, `c`, {z: `actual`}) // `default`
Returns any a property or default
Grab a property from an object or return null
Parameters
property string a propertyinput any an object to grab things fromExamples
import {prop} from 'f-utility'
path(`c`, {c: `actual`}) // `actual`
path(`c`, {z: `actual`}) // null
Returns any a property or null
Grab a property from an object and compare it with a given function
Parameters
is function an assertion functionlenses Array<strings> a propertyinput any an object to grab things fromReturns boolean a truthy value
Grab a property from an object and compare it with a given value via ===
Parameters
equiv any equivalent valuelenses Array<strings> a propertyinput any an object to grab things fromReturns boolean a truthy value
Grab a property from an object and compare it with a given function
Parameters
equiv any equivalent valueproperty string a propertyinput any an object to grab things fromReturns boolean a truthy value
Grab a property from an object and compare it with a given value via ===
Parameters
equiv any equivalent valueproperty string a propertyinput any an object to grab things fromReturns boolean a truthy value
Simple wrap for floor( x * random )
Parameters
x number a numberExamples
import {random} from 'f-utility'
const {floor} = random
floor(0) // 0
Returns number x - a rounded number
Simple wrap for floor( x * random ) + min
Parameters
Examples
import {random} from 'f-utility'
const {floorMin} = random
floor(0, 0) // 0
Returns number a number that is randomly above the min
Shuffle the contents of an array
Parameters
list Array an array to be shuffledExamples
import {random} from 'f-utility'
const {shuffle} = random
const shuffle(`abcde`.split(``)) // randomly shuffled array
Returns Array shuffled
Take values randomly from objects or arrays
Parameters
encase boolean do we want to return the unwrapped value?input mixed an array or objectExamples
import {random} from 'f-utility'
const {take} = random
const a2e = `abcde`.split(``)
const a2eObject = {a: 1, b: 2, c: 3}
take(true, a2e) // [`a`]
take(true, a2e) // [`d`]
take(false, a2e) // `c`
take(false, a2e) // `b`
take(true, a2eObject) // {b: 2}
take(true, a2eObject) // {c: 3}
take(false, a2eObject) // 1
take(false, a2eObject) // 3
Returns mixed either random values from the object.values or the array values, possibly wrapped
partially-applied take - pull values randomly from an array or an object
Parameters
Examples
import {random} from 'f-utility'
const {pick} = random
pick(`abcde`.split(``)) // `a`
pick(`abcde`.split(``)) // `d`
pick(`abcde`.split(``)) // `b`
partially-applied take - pull values randomly from an array or an object
Parameters
Examples
import {random} from 'f-utility'
const {pick} = random
pick(`abcde`.split(``)) // [`a`]
pick(`abcde`.split(``)) // [`d`]
pick(`abcde`.split(``)) // [`b`]
pull some number of values from an array or object
Parameters
howMany number how many values to takeofThing mixed array or objectExamples
import {random} from 'f-utility'
const {allot} = random
const a2e = `abcde`.split(``)
allot(3, a2e) // [`d`, `b`, `c`]
allot(3, a2e) // [`a`, `e`, `c`]
allot(3, a2e) // [`e`, `b`, `a`]
const a2eObject = {a: 1, b: 2, c: 3, d: 4, e: 5}
allot(3, a2eObject) // {d: 4, e: 5, a: 1}
allot(3, a2eObject) // {a: 1, c: 3, a: 1}
Returns Array values
generate a "word" of some known length
Parameters
source Array<strings> which characters should be used?howLong number how many characters should be used?Examples
import {random} from 'f-utility'
const {wordSource} = random
const dna = wordSource([`g`, `a`, `t`, `c`])
dna(7) // `gattaca`
Returns string word
generate a "word" of some known length
Parameters
x number how many characters should be used?Examples
import {random} from 'f-utility'
const {word} = random
word(5) // `lrmbs`
Returns string word
Simple wrap for round( x * random )
Parameters
x number a numberExamples
import {random} from 'f-utility'
random(5) // 1
random(5) // 3
random(0) // 0
Returns number x - a rounded and randomized number
functor.reduce but curried and fast
Parameters
Examples
import {reduce} from 'f-utility'
const sum = reduce((agg, x) => agg + x, 0)
sum([1, 2, 3, 4, 5]) // 15
Returns any mixed reduction
array.filter((x) => !fn(x)) but inverted order, curried and fast
Parameters
Examples
import {reject} from 'f-utility'
reject((x) => x % 2 !== 0, [1,2,3,4,5,6,7,8]) // [2,4,6,8]
Returns Array filtered iterable
string.split(x) but delegatee last
Parameters
Examples
import {split} from `f-utility`
split(`x`, `1x2x3`) // [`1`, `2`, `3`]
Returns Array<strings>
string.replace but delegatee last https://developer.mozilla.org/en-US/docs/Web/JavaScript/Reference/Global_Objects/String/replace
Parameters
Returns string string with replacements
string.trim() but delegatee last
Parameters
string string to trimExamples
import {trim} from `f-utility`
trim(` 20932 `) // `20932`
Returns string trimmed
a ternary statement, but curried and lazy
Parameters
cn any anything to be evaluated as truthya any anythingb any anythingExamples
import {ternary} from `f-utility`
ternary(true, `a`, `b`) // `a`
ternary(false, `a`, `b`) // `b`
Returns mixed a / b
a ternary statement, but curried and lazy and where each case is a function
Parameters
cnFn function anything to be evaluated as truthyaFn function a functionbFn function b functiono mixed inputExamples
import {triplet} from 'f-utility'
const test = (x) => x % 2 === 0
const double = (x) => x * 2
const half = (x) => x / 2
triplet(test, double, half, 100) // 200
triplet(test, double, half, 5) // 2.5
Returns any anything
returns boolean based on type
Parameters
type stringx any anythingExamples
import {isTypeof} from 'f-utility'
isTypeof(`boolean`, true) // true
isTypeof(`boolean`, `nope`) // false
Returns boolean whether x is typeof type
test whether something is a boolean
Parameters
x any anythingExamples
import {isBoolean} from 'f-utility'
isBoolean(true) // true
isBoolean(1) // false
isBoolean(`a`) // false
isBoolean([`a`]) // false
Returns boolean true if the input is a boolean
test whether something is a number
Parameters
x any anythingExamples
import {isNumber} from 'f-utility'
isNumber(true) // false
isNumber(1) // true
isNumber(`a`) // false
isNumber([`a`]) // false
Returns boolean true if the input is a number
test whether something is a function
Parameters
x any anythingExamples
import {isFunction} from 'f-utility'
isFunction(true) // false
isFunction(1) // false
isFunction(`a`) // false
isFunction([`a`]) // false
isFunction(() => {}) // true
Returns boolean true if the input is a function
test whether something is a string
Parameters
x any anythingExamples
import {isString} from 'f-utility'
isString(true) // false
isString(1) // false
isString(`a`) // true
isString([`a`]) // false
isString(() => {}) // false
Returns boolean true if the input is a string
test whether something is null-ish
Parameters
x any anythingExamples
import {isNil} from 'f-utility'
isNil(true) // false
isNil(1) // false
isNil(`a`) // false
isNil([`a`]) // false
isNil({}) // false
isNil(null) // true
isNil(undefined) // true
Returns boolean true if the input is null-ish
test whether something is an object
Parameters
x any anythingExamples
import {isObject} from 'f-utility'
isObject(true) // false
isObject(1) // false
isObject(`a`) // false
isObject([`a`]) // true
isObject({}) // true
isObject(null) // true
Returns boolean true if the input is a object
test whether something is an array
Parameters
x any anythingExamples
import {isArray} from 'f-utility'
isArray(true) // false
isArray(1) // false
isArray(`a`) // false
isArray([`a`]) // true
isArray({}) // false
isArray(null) // false
isArray(undefined) // false
Returns boolean true if the input is an array
test whether something is a non-null object which isn't an array
Parameters
x any anythingExamples
import {isDistinctObject} from 'f-utility'
isDistinctObject(true) // false
isDistinctObject(1) // false
isDistinctObject(`a`) // false
isDistinctObject([`a`]) // false
isDistinctObject({}) // true
isDistinctObject(null) // false
isDistinctObject(undefined) // false
Returns boolean true if the input is an object that isn't an array and isn't null
array.some(fn) but curried and lazy
Parameters
Examples
import {some} from 'f-utility'
some((x) => x === `j`, [`j`, `k`, `l`]) // true
some((x) => x === `z`, [`j`, `k`, `l`]) // false
Returns boolean
array.every(fn) but curried and lazy
Parameters
Examples
import {isNumber, every} from 'f-utility'
every(isNumber, [0, 1, 2, 3, 4]) // true
every(isNumber, [0, 1, 2, 3, `four`]) // false
Returns boolean
FAQs
functional utilities
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We found that f-utility demonstrated a not healthy version release cadence and project activity because the last version was released a year ago. It has 1 open source maintainer collaborating on the project.
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