Rambdax

Extended version of Rambda(utility library) - Documentation

Rambda is smaller and faster alternative to the popular functional programming library Ramda. - Documentation

❯ Differences between Rambda and Rambdax

Rambdax passthrough all Rambda methods and introduce some new functions.

The idea of Rambdax is to extend Rambda without worring for Ramda compatibility.

❯ Example use

import { composeAsync, filter, delay, mapAsync } from 'rambdax'

const result = await composeAsync(
  mapAsync(async x => {
    await delay(100)
    return x + 1
  }),
  filter(x => x > 1)
)([1, 2, 3])
// => [3, 4]

You can test this example in Rambda's REPL

• Differences between Rambda and Ramda
• API
• Changelog

❯ Rambdax's advantages

TypeScript included

TypeScript definitions are included in the library, in comparison to Ramda, where you need to additionally install @types/ramda.

Still, you need to be aware that functional programming features in TypeScript are in development, which means that using R.compose/R.pipe can be problematic.

Important - Rambdax version 9.0.0(or higher) requires TypeScript version 4.3.3(or higher).

Dot notation for R.path, R.paths, R.assocPath and R.lensPath

Standard usage of R.path is R.path(['a', 'b'], {a: {b: 1} }).

In Rambda you have the choice to use dot notation(which is arguably more readable):

R.path('a.b', {a: {b: 1} })

Comma notation for R.pick and R.omit

Similar to dot notation, but the separator is comma(,) instead of dot(.).

R.pick('a,b', {a: 1 , b: 2, c: 3} })
// No space allowed between properties

Extendable with Ramda community projects

Rambdax implements some methods from Ramda community projects, such as R.lensSatisfies, R.lensEq and R.viewOr.

Understandable source code due to little usage of internals

Ramda uses a lot of internals, which hides a lot of logic. Reading the full source code of a method can be challenging.

Better VSCode experience

If the project is written in Javascript, then go to source definition action will lead you to actual implementation of the method.

Alternative TS definitions

Alternative TS definitions are available as rambdax/immutable. These are Rambdax definitions linted with ESLint functional/prefer-readonly-type plugin.

❯ Missing Ramda methods

Click to see the full list of 43 Ramda methods not implemented in Rambda and their status.

• into

• invert

• invertObj

• invoker

• keysIn

• lift

• liftN

• mapAccum

• mapAccumRight

• memoizeWith

• mergeDeepWith

• mergeDeepWithKey

• mergeWithKey

• nAry

• nthArg

• o

• otherwise

• pair

• partialRight

• pathSatisfies

• pipeWith

• project

• promap

• reduceRight

• reduceWhile

• reduced

• remove

• scan

• sequence

• splitWhenever

• symmetricDifferenceWith

• andThen

• toPairsIn

• unary

• uncurryN

• unfold

• unionWith

• until

• useWith

• valuesIn

• xprod

• thunkify

• default

  Most of above methods are in progress to be added to Rambda. The following methods are not going to be added:

• __ - placeholder method allows user to further customize the method call. While, it seems useful initially, the price is too high in terms of complexity for TypeScript definitions. If it is not easy exressable in TypeScript, it is not worth it as Rambda is a TypeScript first library.

• construct - Using classes is not very functional programming oriented.

• constructN - same as above

• transduce - currently is out of focus

• traverse - same as above

❯ Install

• yarn add rambdax

• For UMD usage either use ./dist/rambdax.umd.js or the following CDN link:

https://unpkg.com/rambdax@CURRENT_VERSION/dist/rambdax.umd.js

• with deno

import {add} from "https://deno.land/x/rambda/mod.ts";

Differences between Rambda and Ramda

• Rambda's type detects async functions and unresolved Promises. The returned values are 'Async' and 'Promise'.

• Rambda's type handles NaN input, in which case it returns NaN.

• Rambda's forEach can iterate over objects not only arrays.

• Rambda's map, filter, partition when they iterate over objects, they pass property and input object as predicate's argument.

• Rambda's filter returns empty array with bad input(null or undefined), while Ramda throws.

• Ramda's clamp work with strings, while Rambda's method work only with numbers.

• Ramda's indexOf/lastIndexOf work with strings and lists, while Rambda's method work only with lists as iterable input.

• Error handling, when wrong inputs are provided, may not be the same. This difference will be better documented once all brute force tests are completed.

• TypeScript definitions between rambda and @types/ramda may vary.

❯ Benchmarks

Click to expand all benchmark results

There are methods which are benchmarked only with Ramda and Rambda(i.e. no Lodash).

Note that some of these methods, are called with and without curring. This is done in order to give more detailed performance feedback.

The benchmarks results are produced from latest versions of Rambda, Lodash(4.17.21) and Ramda(0.29.1).

method	Rambda	Ramda	Lodash
add	🚀 Fastest	21.52% slower	82.15% slower
adjust	8.48% slower	🚀 Fastest	🔳
all	🚀 Fastest	7.18% slower	🔳
allPass	🚀 Fastest	88.25% slower	🔳
allPass	🚀 Fastest	98.56% slower	🔳
and	🚀 Fastest	89.09% slower	🔳
any	🚀 Fastest	92.87% slower	45.82% slower
anyPass	🚀 Fastest	98.25% slower	🔳
append	🚀 Fastest	2.07% slower	🔳
applySpec	🚀 Fastest	80.43% slower	🔳
assoc	72.32% slower	60.08% slower	🚀 Fastest
clone	🚀 Fastest	91.86% slower	86.48% slower
compose	6.07% slower	16.89% slower	🚀 Fastest
converge	78.63% slower	🚀 Fastest	🔳
curry	🚀 Fastest	28.86% slower	🔳
curryN	🚀 Fastest	41.05% slower	🔳
defaultTo	🚀 Fastest	48.91% slower	🔳
drop	🚀 Fastest	82.35% slower	🔳
dropLast	🚀 Fastest	86.74% slower	🔳
equals	58.37% slower	96.73% slower	🚀 Fastest
filter	6.7% slower	72.03% slower	🚀 Fastest
find	🚀 Fastest	85.14% slower	42.65% slower
findIndex	🚀 Fastest	86.48% slower	72.27% slower
flatten	🚀 Fastest	85.68% slower	3.57% slower
ifElse	🚀 Fastest	58.56% slower	🔳
includes	🚀 Fastest	81.64% slower	🔳
indexOf	🚀 Fastest	80.17% slower	🔳
indexOf	🚀 Fastest	82.2% slower	🔳
init	🚀 Fastest	92.24% slower	13.3% slower
is	🚀 Fastest	57.69% slower	🔳
isEmpty	🚀 Fastest	97.14% slower	54.99% slower
last	🚀 Fastest	93.43% slower	5.28% slower
lastIndexOf	🚀 Fastest	85.19% slower	🔳
map	🚀 Fastest	86.6% slower	11.73% slower
match	🚀 Fastest	44.83% slower	🔳
merge	🚀 Fastest	12.21% slower	55.76% slower
none	🚀 Fastest	96.48% slower	🔳
objOf	🚀 Fastest	38.05% slower	🔳
omit	🚀 Fastest	69.95% slower	97.34% slower
over	🚀 Fastest	56.23% slower	🔳
path	37.81% slower	77.81% slower	🚀 Fastest
pick	🚀 Fastest	19.07% slower	80.2% slower
pipe	🚀 Fastest	0.11% slower	🔳
prop	🚀 Fastest	87.95% slower	🔳
propEq	🚀 Fastest	91.92% slower	🔳
range	🚀 Fastest	61.8% slower	57.44% slower
reduce	60.48% slower	77.1% slower	🚀 Fastest
repeat	48.57% slower	68.98% slower	🚀 Fastest
replace	33.45% slower	33.99% slower	🚀 Fastest
set	🚀 Fastest	50.35% slower	🔳
sort	🚀 Fastest	40.23% slower	🔳
sortBy	🚀 Fastest	25.29% slower	56.88% slower
split	🚀 Fastest	55.37% slower	17.64% slower
splitEvery	🚀 Fastest	71.98% slower	🔳
take	🚀 Fastest	91.96% slower	4.72% slower
takeLast	🚀 Fastest	93.39% slower	19.22% slower
test	🚀 Fastest	82.34% slower	🔳
type	🚀 Fastest	48.6% slower	🔳
uniq	🚀 Fastest	84.9% slower	🔳
uniqBy	51.93% slower	🚀 Fastest	🔳
uniqWith	8.29% slower	🚀 Fastest	🔳
uniqWith	14.23% slower	🚀 Fastest	🔳
update	🚀 Fastest	52.35% slower	🔳
view	🚀 Fastest	76.15% slower	🔳

❯ Used by

• ESLint plugin Mocha

• WatermelonDB

• Walmart Canada reported by w-b-dev

• VSCode Slack integration

• Webpack PostCSS

• MobX-State-Tree decorators

• Rewrite of the Betaflight configurator

• MineFlayer plugin

API

add

It adds a and b.

💥 It doesn't work with strings, as the inputs are parsed to numbers before calculation.

Try this R.add example in Rambda REPL

addIndex

Try this R.addIndex example in Rambda REPL

addIndexRight

Same as R.addIndex, but it will passed indexes are decreasing, instead of increasing.

adjust

adjust<T>(index: number, replaceFn: (x: T) => T, list: T[]): T[]

It replaces index in array list with the result of replaceFn(list[i]).

const result = R.adjust(
  0,
  a => a + 1,
  [0, 100]
) // => [1, 100]

Try this R.adjust example in Rambda REPL

R.adjust source

import { cloneList } from './_internals/cloneList.js'
import { curry } from './curry.js'

function adjustFn(
  index, replaceFn, list
){
  const actualIndex = index < 0 ? list.length + index : index
  if (index >= list.length || actualIndex < 0) return list

  const clone = cloneList(list)
  clone[ actualIndex ] = replaceFn(clone[ actualIndex ])

  return clone
}

export const adjust = curry(adjustFn)

Tests

import { add } from './add.js'
import { adjust } from './adjust.js'
import { pipe } from './pipe.js'

const list = [ 0, 1, 2 ]
const expected = [ 0, 11, 2 ]

test('happy', () => {})

test('happy', () => {
  expect(adjust(
    1, add(10), list
  )).toEqual(expected)
})

test('with curring type 1 1 1', () => {
  expect(adjust(1)(add(10))(list)).toEqual(expected)
})

test('with curring type 1 2', () => {
  expect(adjust(1)(add(10), list)).toEqual(expected)
})

test('with curring type 2 1', () => {
  expect(adjust(1, add(10))(list)).toEqual(expected)
})

test('with negative index', () => {
  expect(adjust(
    -2, add(10), list
  )).toEqual(expected)
})

test('when index is out of bounds', () => {
  const list = [ 0, 1, 2, 3 ]
  expect(adjust(
    4, add(1), list
  )).toEqual(list)
  expect(adjust(
    -5, add(1), list
  )).toEqual(list)
})

all

all<T>(predicate: (x: T) => boolean, list: T[]): boolean

It returns true, if all members of array list returns true, when applied as argument to predicate function.

const list = [ 0, 1, 2, 3, 4 ]
const predicate = x => x > -1

const result = R.all(predicate, list)
// => true

Try this R.all example in Rambda REPL

R.all source

export function all(predicate, list){
  if (arguments.length === 1) return _list => all(predicate, _list)

  for (let i = 0; i < list.length; i++){
    if (!predicate(list[ i ])) return false
  }

  return true
}

Tests

import { all } from './all.js'

const list = [ 0, 1, 2, 3, 4 ]

test('when true', () => {
  const fn = x => x > -1

  expect(all(fn)(list)).toBeTrue()
})

test('when false', () => {
  const fn = x => x > 2

  expect(all(fn, list)).toBeFalse()
})

allFalse

allFalse(...inputs: any[]): boolean

It returns true if all inputs arguments are falsy(empty objects and empty arrays are considered falsy).

Functions are valid inputs, but these functions cannot have their own arguments.

This method is very similar to R.anyFalse, R.anyTrue and R.allTrue

R.allFalse(0, null, [], {}, '', () => false)
// => true

Try this R.allFalse example in Rambda REPL

R.allFalse source

import { isTruthy } from './_internals/isTruthy.js'
import { type } from './type.js'

export function allFalse(...inputs){
  let counter = 0
  while (counter < inputs.length){
    const x = inputs[ counter ]

    if (type(x) === 'Function'){
      if (isTruthy(x())){
        return false
      }
    } else if (isTruthy(x)){
      return false
    }

    counter++
  }

  return true
}

Tests

import { runTests } from 'helpers-fn'

import { allFalse } from './allFalse.js'

const happy = { ok : [ () => false, () => [], () => {}, null, false, [] ] }
const withArray = { fail : [ ...happy.ok, [ 1 ] ] }
const withObject = { fail : [ ...happy.ok, { a : 1 } ] }
const withFunction = { fail : [ ...happy.ok, () => ({ a : 1 }) ] }
const withBoolean = { fail : [ ...happy.ok, true ] }

const testData = {
  label : 'R.allFalse',
  data  : [ happy, withArray, withObject, withFunction, withBoolean ],
  fn    : input => allFalse(...input),
}
runTests(testData)

allPass

allPass<T>(predicates: ((x: T) => boolean)[]): (input: T) => boolean

It returns true, if all functions of predicates return true, when input is their argument.

const input = {
  a : 1,
  b : 2,
}
const predicates = [
  x => x.a === 1,
  x => x.b === 2,
]
const result = R.allPass(predicates)(input) // => true

Try this R.allPass example in Rambda REPL

R.allPass source

export function allPass(predicates){
  return (...input) => {
    let counter = 0
    while (counter < predicates.length){
      if (!predicates[ counter ](...input)){
        return false
      }
      counter++
    }

    return true
  }
}

Tests

import { allPass } from './allPass.js'

test('happy', () => {
  const rules = [ x => typeof x === 'number', x => x > 10, x => x * 7 < 100 ]

  expect(allPass(rules)(11)).toBeTrue()

  expect(allPass(rules)(undefined)).toBeFalse()
})

test('when returns true', () => {
  const conditionArr = [ val => val.a === 1, val => val.b === 2 ]

  expect(allPass(conditionArr)({
    a : 1,
    b : 2,
  })).toBeTrue()
})

test('when returns false', () => {
  const conditionArr = [ val => val.a === 1, val => val.b === 3 ]

  expect(allPass(conditionArr)({
    a : 1,
    b : 2,
  })).toBeFalse()
})

test('works with multiple inputs', () => {
  const fn = function (
    w, x, y, z
  ){
    return w + x === y + z
  }
  expect(allPass([ fn ])(
    3, 3, 3, 3
  )).toBeTrue()
})

allTrue

allTrue(...input: any[]): boolean

It returns true if all inputs arguments are truthy(empty objects and empty arrays are considered falsy).

R.allTrue(1, true, {a: 1}, [1], 'foo', () => true)
// => true

Try this R.allTrue example in Rambda REPL

R.allTrue source

import { isFalsy } from './_internals/isFalsy.js'
import { type } from './type.js'

export function allTrue(...inputs){
  let counter = 0
  while (counter < inputs.length){
    const x = inputs[ counter ]

    if (type(x) === 'Function'){
      if (isFalsy(x())){
        return false
      }
    } else if (isFalsy(x)){
      return false
    }

    counter++
  }

  return true
}

Tests

import { allTrue } from './allTrue.js'

test('with functions', () => {
  const foo = () => 1
  const bar = () => false
  const baz = () => JSON.parse('{sda')
  const result = allTrue(
    foo, bar, baz
  )
  expect(result).toBeFalse()
})

test('usage with non boolean', () => {
  const foo = { a : 1 }
  const baz = [ 1, 2, 3 ]

  const result = allTrue(
    foo, foo, baz
  )
  expect(result).toBeTrue()
})

test('usage with boolean', () => {
  const foo = 4
  const baz = [ 1, 2, 3 ]

  const result = allTrue(foo > 2, baz.length === 3)
  expect(result).toBeTrue()
})

test('escapes early - case 0', () => {
  const foo = undefined
  const result = allTrue(foo, () => foo.a)
  expect(result).toBeFalse()
})

test('escapes early - case 1', () => {
  const foo = null
  const result = allTrue(foo, () => foo.a)
  expect(result).toBeFalse()
})

test('escapes early - case 2', () => {
  const foo = { a : 'bar' }
  const result = allTrue(
    foo, foo.a, foo.a.b
  )
  expect(result).toBeFalse()
})

test('escapes early - case 3', () => {
  const foo = { a : { b : 'foo' } }
  const result = allTrue(
    foo,
    () => foo.a,
    () => foo.a.b
  )
  expect(result).toBeTrue()
})

allType

allType(targetType: RambdaTypes): (...input: any[]) => boolean

It returns a function which will return true if all of its inputs arguments belong to targetType.

💥 targetType is one of the possible returns of R.type

const targetType = 'String'

const result = R.allType(
  targetType
)('foo', 'bar', 'baz')
// => true

Try this R.allType example in Rambda REPL

R.allType source

import { type } from './type.js'

export function allType(targetType){
  return (...inputs) => {
    let counter = 0

    while (counter < inputs.length){
      if (type(inputs[ counter ]) !== targetType){
        return false
      }
      counter++
    }

    return true
  }
}

Tests

import { allType } from './allType.js'

test('when true', () => {
  const result = allType('Array')(
    [ 1, 2, 3 ], [], [ null ]
  )

  expect(result).toBeTrue()
})

test('when false', () => {
  const result = allType('String')(
    1, undefined, null, []
  )

  expect(result).toBeFalse()
})

always

It returns function that always returns x.

Try this R.always example in Rambda REPL

and

Logical AND

Try this R.and example in Rambda REPL

any

any<T>(predicate: (x: T) => boolean, list: T[]): boolean

It returns true, if at least one member of list returns true, when passed to a predicate function.

const list = [1, 2, 3]
const predicate = x => x * x > 8
R.any(fn, list)
// => true

Try this R.any example in Rambda REPL

R.any source

export function any(predicate, list){
  if (arguments.length === 1) return _list => any(predicate, _list)

  let counter = 0
  while (counter < list.length){
    if (predicate(list[ counter ], counter)){
      return true
    }
    counter++
  }

  return false
}

Tests

import { any } from './any.js'

const list = [ 1, 2, 3 ]

test('happy', () => {
  expect(any(x => x < 0, list)).toBeFalse()
})

test('with curry', () => {
  expect(any(x => x > 2)(list)).toBeTrue()
})

anyFalse

anyFalse(...input: any[]): boolean

It returns true if any of inputs is falsy(empty objects and empty arrays are considered falsy).

R.anyFalse(1, {a: 1}, [1], () => false)
// => true

Try this R.anyFalse example in Rambda REPL

R.anyFalse source

import { isFalsy } from './_internals/isFalsy.js'
import { type } from './type.js'

export function anyFalse(...inputs){
  let counter = 0
  while (counter < inputs.length){
    const x = inputs[ counter ]

    if (type(x) === 'Function'){
      if (isFalsy(x())){
        return true
      }
    } else if (isFalsy(x)){
      return true
    }

    counter++
  }

  return false
}

Tests

import { anyFalse } from './anyFalse.js'

test('when true', () => {
  expect(anyFalse(
    true, true, false
  )).toBeTruthy()
})

test('when false', () => {
  expect(anyFalse(true, true)).toBeFalsy()
})

test('supports function', () => {
  expect(anyFalse(
    true,
    () => true,
    () => false
  )).toBeTruthy()
})

anyPass

anyPass<T>(predicates: ((x: T) => boolean)[]): (input: T) => boolean

It accepts list of predicates and returns a function. This function with its input will return true, if any of predicates returns true for this input.

const isBig = x => x > 20
const isOdd = x => x % 2 === 1
const input = 11

const fn = R.anyPass(
  [isBig, isOdd]
)

const result = fn(input) 
// => true

Try this R.anyPass example in Rambda REPL

R.anyPass source

export function anyPass(predicates){
  return (...input) => {
    let counter = 0
    while (counter < predicates.length){
      if (predicates[ counter ](...input)){
        return true
      }
      counter++
    }

    return false
  }
}

Tests

import { anyPass } from './anyPass.js'

test('happy', () => {
  const rules = [ x => typeof x === 'string', x => x > 10 ]
  const predicate = anyPass(rules)
  expect(predicate('foo')).toBeTrue()
  expect(predicate(6)).toBeFalse()
})

test('happy', () => {
  const rules = [ x => typeof x === 'string', x => x > 10 ]

  expect(anyPass(rules)(11)).toBeTrue()
  expect(anyPass(rules)(undefined)).toBeFalse()
})

const obj = {
  a : 1,
  b : 2,
}

test('when returns true', () => {
  const conditionArr = [ val => val.a === 1, val => val.a === 2 ]

  expect(anyPass(conditionArr)(obj)).toBeTrue()
})

test('when returns false + curry', () => {
  const conditionArr = [ val => val.a === 2, val => val.b === 3 ]

  expect(anyPass(conditionArr)(obj)).toBeFalse()
})

test('with empty predicates list', () => {
  expect(anyPass([])(3)).toBeFalse()
})

test('works with multiple inputs', () => {
  const fn = function (
    w, x, y, z
  ){
    console.log(
      w, x, y, z
    )

    return w + x === y + z
  }
  expect(anyPass([ fn ])(
    3, 3, 3, 3
  )).toBeTrue()
})

anyTrue

anyTrue(...input: any[]): boolean

It returns true if any of inputs arguments are truthy(empty objects and empty arrays are considered falsy).

R.anyTrue(0, null, [], {}, '', () => true)
// => true

Try this R.anyTrue example in Rambda REPL

R.anyTrue source

import { isTruthy } from './_internals/isTruthy.js'
import { type } from './type.js'

export function anyTrue(...inputs){
  let counter = 0
  while (counter < inputs.length){
    const x = inputs[ counter ]

    if (type(x) === 'Function'){
      if (isTruthy(x())){
        return true
      }
    } else if (isTruthy(x)){
      return true
    }

    counter++
  }

  return false
}

Tests

import { anyTrue } from './anyTrue.js'

test('when true', () => {
  expect(anyTrue(
    true, true, false
  )).toBeTruthy()
})

test('when false', () => {
  expect(anyTrue(
    false, false, false
  )).toBeFalsy()
})

test('supports function', () => {
  expect(anyTrue(
    false,
    false,
    false,
    () => false,
    () => true
  )).toBeTruthy()
})

anyType

anyType(targetType: RambdaTypes): (...input: any[]) => boolean

It returns a function which will return true if at least one of its inputs arguments belongs to targetType.

targetType is one of the possible returns of R.type

💥 targetType is one of the possible returns of R.type

const targetType = 'String'

const result = R.anyType(
  targetType
)(1, {}, 'foo')
// => true

Try this R.anyType example in Rambda REPL

R.anyType source

import { type } from './type.js'

export function anyType(targetType){
  return (...inputs) => {
    let counter = 0

    while (counter < inputs.length){
      if (type(inputs[ counter ]) === targetType){
        return true
      }
      counter++
    }

    return false
  }
}

Tests

import { anyType } from './anyType.js'

test('when true', () => {
  const result = anyType('Array')(
    1, undefined, null, []
  )

  expect(result).toBeTrue()
})

test('when false', () => {
  const result = anyType('String')(
    1, undefined, null, []
  )

  expect(result).toBeFalse()
})

ap

ap<T, U>(fns: Array<(a: T) => U>[], vs: T[]): U[]

It takes a list of functions and a list of values. Then it returns a list of values obtained by applying each function to each value.

const result = R.ap(
  [
    x => x + 1,
    x => x + 2,
  ],
  [1, 2, 3]
)
// => [2, 3, 4, 3, 4, 5]

Try this R.ap example in Rambda REPL

R.ap source

export function ap(functions, input){
  if (arguments.length === 1){
    return _inputs => ap(functions, _inputs)
  }

  return functions.reduce((acc, fn) => [ ...acc, ...input.map(fn) ], [])
}

Tests

import { ap } from './ap.js'

function mult2(x){
  return x * 2
}
function plus3(x){
  return x + 3
}

test('happy', () => {
  expect(ap([ mult2, plus3 ], [ 1, 2, 3 ])).toEqual([ 2, 4, 6, 4, 5, 6 ])
})

aperture

aperture<N extends number, T>(n: N, list: T[]): Array<Tuple<T, N>> | []

It returns a new list, composed of consecutive n-tuples from a list.

const result = R.aperture(2, [1, 2, 3, 4])
// => [[1, 2], [2, 3], [3, 4]]

Try this R.aperture example in Rambda REPL

R.aperture source

export function aperture(step, list){
  if (arguments.length === 1){
    return _list => aperture(step, _list)
  }
  if (step > list.length) return []
  let idx = 0
  const limit = list.length - (step - 1)
  const acc = new Array(limit)
  while (idx < limit){
    acc[ idx ] = list.slice(idx, idx + step)
    idx += 1
  }

  return acc
}

Tests

import { aperture } from './aperture.js'

const list = [ 1, 2, 3, 4, 5, 6, 7 ]

test('happy', () => {
  expect(aperture(1, list)).toEqual([ [ 1 ], [ 2 ], [ 3 ], [ 4 ], [ 5 ], [ 6 ], [ 7 ] ])
  expect(aperture(2, list)).toEqual([
    [ 1, 2 ],
    [ 2, 3 ],
    [ 3, 4 ],
    [ 4, 5 ],
    [ 5, 6 ],
    [ 6, 7 ],
  ])
  expect(aperture(3, list)).toEqual([
    [ 1, 2, 3 ],
    [ 2, 3, 4 ],
    [ 3, 4, 5 ],
    [ 4, 5, 6 ],
    [ 5, 6, 7 ],
  ])
  expect(aperture(8, list)).toEqual([])
})

append

append<T>(xToAppend: T, iterable: T[]): T[]

It adds element x at the end of iterable.

const x = 'foo'

const result = R.append(x, ['bar', 'baz'])
// => ['bar', 'baz', 'foo']

Try this R.append example in Rambda REPL

R.append source

import { cloneList } from './_internals/cloneList.js'

export function append(x, input){
  if (arguments.length === 1) return _input => append(x, _input)

  if (typeof input === 'string') return input.split('').concat(x)

  const clone = cloneList(input)
  clone.push(x)

  return clone
}

Tests

import { append } from './append.js'

test('happy', () => {
  expect(append('tests', [ 'write', 'more' ])).toEqual([
    'write',
    'more',
    'tests',
  ])
})

test('append to empty array', () => {
  expect(append('tests')([])).toEqual([ 'tests' ])
})

test('with strings', () => {
  expect(append('o', 'fo')).toEqual([ 'f', 'o', 'o' ])
})

apply

apply<T = any>(fn: (...args: any[]) => T, args: any[]): T

It applies function fn to the list of arguments.

This is useful for creating a fixed-arity function from a variadic function. fn should be a bound function if context is significant.

const result = R.apply(Math.max, [42, -Infinity, 1337])
// => 1337

Try this R.apply example in Rambda REPL

R.apply source

export function apply(fn, args){
  if (arguments.length === 1){
    return _args => apply(fn, _args)
  }

  return fn.apply(this, args)
}

Tests

import { apply } from './apply.js'
import { bind } from './bind.js'
import { identity } from './identity.js'

test('happy', () => {
  expect(apply(identity, [ 1, 2, 3 ])).toBe(1)
})

test('applies function to argument list', () => {
  expect(apply(Math.max, [ 1, 2, 3, -99, 42, 6, 7 ])).toBe(42)
})

test('provides no way to specify context', () => {
  const obj = {
    method (){
      return this === obj
    },
  }
  expect(apply(obj.method, [])).toBeFalse()
  expect(apply(bind(obj.method, obj), [])).toBeTrue()
})

applyDiff

applyDiff<Output>(rules: ApplyDiffRule[], obj: object): Output

It changes paths in an object according to a list of operations. Valid operations are add, update and delete. Its use-case is while writing tests and you need to change the test data.

Note, that you cannot use update operation, if the object path is missing in the input object. Also, you cannot use add operation, if the object path has a value.

const obj = {a: {b:1, c:2}}
const rules = [
  {op: 'remove', path: 'a.c'},
  {op: 'add', path: 'a.d', value: 4},
  {op: 'update', path: 'a.b', value: 2},
]
const result = R.applyDiff(rules, Record<string, unknown>)
const expected = {a: {b: 2, d: 4}}

// => `result` is equal to `expected`

Try this R.applyDiff example in Rambda REPL

R.applyDiff source

import { createPath } from './_internals/createPath.js'
import { assocPathFn } from './assocPath.js'
import { path as pathModule } from './path.js'
const ALLOWED_OPERATIONS = [ 'remove', 'add', 'update' ]

export function removeAtPath(path, obj){
  const p = createPath(path)

  const len = p.length
  if (len === 0) return
  if (len === 1) return delete obj[ p[ 0 ] ]
  if (len === 2) return delete obj[ p[ 0 ] ][ p[ 1 ] ]
  if (len === 3) return delete obj[ p[ 0 ] ][ p[ 1 ] ][ p[ 2 ] ]
  if (len === 4) return delete obj[ p[ 0 ] ][ p[ 1 ] ][ p[ 2 ] ][ p[ 3 ] ]
  if (len === 5) return delete obj[ p[ 0 ] ][ p[ 1 ] ][ p[ 2 ] ][ p[ 3 ] ][ p[ 4 ] ]
  if (len === 6)
    return delete obj[ p[ 0 ] ][ p[ 1 ] ][ p[ 2 ] ][ p[ 3 ] ][ p[ 4 ] ][ p[ 5 ] ]

  if (len === 7)
    return delete obj[ p[ 0 ] ][ p[ 1 ] ][ p[ 2 ] ][ p[ 3 ] ][ p[ 4 ] ][ p[ 5 ] ][ p[ 6 ] ]

  if (len === 8)
    return delete obj[ p[ 0 ] ][ p[ 1 ] ][ p[ 2 ] ][ p[ 3 ] ][ p[ 4 ] ][ p[ 5 ] ][ p[ 6 ] ][ p[ 7 ] ]

  if (len === 9)
    return delete obj[ p[ 0 ] ][ p[ 1 ] ][ p[ 2 ] ][ p[ 3 ] ][ p[ 4 ] ][ p[ 5 ] ][ p[ 6 ] ][ p[ 7 ] ][ p[ 8 ] ]

  if (len === 10)
    return delete obj[ p[ 0 ] ][ p[ 1 ] ][ p[ 2 ] ][ p[ 3 ] ][ p[ 4 ] ][ p[ 5 ] ][ p[ 6 ] ][ p[ 7 ] ][ p[ 8 ] ][
      p[ 9 ]
    ]

}

export function applyDiff(rules, obj){
  if (arguments.length === 1) return _obj => applyDiff(rules, _obj)

  let clone = { ...obj }

  rules.forEach(({ op, path, value }) => {
    if (!ALLOWED_OPERATIONS.includes(op)) return
    if (op === 'add' && path && value !== undefined){
      if (pathModule(path, obj)) return

      clone = assocPathFn(
        path, value, clone
      )

      return
    }

    if (op === 'remove'){
      if (pathModule(path, obj) === undefined) return

      removeAtPath(path, clone)

      return
    }
    if (op === 'update' && path && value !== undefined){
      if (pathModule(path, obj) === undefined) return

      clone = assocPathFn(
        path, value, clone
      )

    }
  })

  return clone
}

Tests

import { applyDiff } from './applyDiff.js'

test('remove operation', () => {
  const rules = [
    {
      op   : 'remove',
      path : 'a.b',
    },
  ]
  const result = applyDiff(rules, {
    a : {
      b : 1,
      c : 2,
    },
  })
  expect(result).toEqual({ a : { c : 2 } })
})

test('update operation', () => {
  const rules = [
    {
      op    : 'update',
      path  : 'a.b',
      value : 3,
    },
    {
      op    : 'update',
      path  : 'a.c.1',
      value : 3,
    },
    {
      op    : 'update',
      path  : 'a.d',
      value : 3,
    },
  ]
  expect(applyDiff(rules, {
    a : {
      b : 1,
      c : [ 1, 2 ],
    },
  })).toEqual({
    a : {
      b : 3,
      c : [ 1, 3 ],
    },
  })
})

test('add operation', () => {
  const rules = [
    {
      op    : 'add',
      path  : 'a.b',
      value : 3,
    },
    {
      op    : 'add',
      path  : 'a.d',
      value : 3,
    },
  ]
  const result = applyDiff(rules, {
    a : {
      b : 1,
      c : 2,
    },
  })

  expect(result).toEqual({
    a : {
      b : 1,
      c : 2,
      d : 3,
    },
  })
})

applySpec

applySpec<Spec extends Record<string, AnyFunction>>(
  spec: Spec
): (
  ...args: Parameters<ValueOfRecord<Spec>>
) => { [Key in keyof Spec]: ReturnType<Spec[Key]> }

💥 The currying in this function works best with functions with 4 arguments or less. (arity of 4)

const fn = R.applySpec({
  sum: R.add,
  nested: { mul: R.multiply }
})
const result = fn(2, 4) 
// => { sum: 6, nested: { mul: 8 } }

Try this R.applySpec example in Rambda REPL

R.applySpec source

import { isArray } from './_internals/isArray.js'

// recursively traverse the given spec object to find the highest arity function
export function __findHighestArity(spec, max = 0){
  for (const key in spec){
    if (spec.hasOwnProperty(key) === false || key === 'constructor') continue

    if (typeof spec[ key ] === 'object'){
      max = Math.max(max, __findHighestArity(spec[ key ]))
    }

    if (typeof spec[ key ] === 'function'){
      max = Math.max(max, spec[ key ].length)
    }
  }

  return max
}

function __filterUndefined(){
  const defined = []
  let i = 0
  const l = arguments.length
  while (i < l){
    if (typeof arguments[ i ] === 'undefined') break
    defined[ i ] = arguments[ i ]
    i++
  }

  return defined
}

function __applySpecWithArity(
  spec, arity, cache
){
  const remaining = arity - cache.length

  if (remaining === 1)
    return x =>
      __applySpecWithArity(
        spec, arity, __filterUndefined(...cache, x)
      )
  if (remaining === 2)
    return (x, y) =>
      __applySpecWithArity(
        spec, arity, __filterUndefined(
          ...cache, x, y
        )
      )
  if (remaining === 3)
    return (
      x, y, z
    ) =>
      __applySpecWithArity(
        spec, arity, __filterUndefined(
          ...cache, x, y, z
        )
      )
  if (remaining === 4)
    return (
      x, y, z, a
    ) =>
      __applySpecWithArity(
        spec,
        arity,
        __filterUndefined(
          ...cache, x, y, z, a
        )
      )
  if (remaining > 4)
    return (...args) =>
      __applySpecWithArity(
        spec, arity, __filterUndefined(...cache, ...args)
      )

  // handle spec as Array
  if (isArray(spec)){
    const ret = []
    let i = 0
    const l = spec.length
    for (; i < l; i++){
      // handle recursive spec inside array
      if (typeof spec[ i ] === 'object' || isArray(spec[ i ])){
        ret[ i ] = __applySpecWithArity(
          spec[ i ], arity, cache
        )
      }
      // apply spec to the key
      if (typeof spec[ i ] === 'function'){
        ret[ i ] = spec[ i ](...cache)
      }
    }

    return ret
  }

  // handle spec as Object
  const ret = {}
  // apply callbacks to each property in the spec object
  for (const key in spec){
    if (spec.hasOwnProperty(key) === false || key === 'constructor') continue

    // apply the spec recursively
    if (typeof spec[ key ] === 'object'){
      ret[ key ] = __applySpecWithArity(
        spec[ key ], arity, cache
      )
      continue
    }

    // apply spec to the key
    if (typeof spec[ key ] === 'function'){
      ret[ key ] = spec[ key ](...cache)
    }
  }

  return ret
}

export function applySpec(spec, ...args){
  // get the highest arity spec function, cache the result and pass to __applySpecWithArity
  const arity = __findHighestArity(spec)

  if (arity === 0){
    return () => ({})
  }
  const toReturn = __applySpecWithArity(
    spec, arity, args
  )

  return toReturn
}

Tests

import { applySpec as applySpecRamda, nAry } from 'ramda'

import {
  add,
  always,
  compose,
  dec,
  inc,
  map,
  path,
  prop,
  T,
} from '../rambda.js'
import { applySpec } from './applySpec.js'

test('different than Ramda when bad spec', () => {
  const result = applySpec({ sum : { a : 1 } })(1, 2)
  const ramdaResult = applySpecRamda({ sum : { a : 1 } })(1, 2)
  expect(result).toEqual({})
  expect(ramdaResult).toEqual({ sum : { a : {} } })
})

test('works with empty spec', () => {
  expect(applySpec({})()).toEqual({})
  expect(applySpec([])(1, 2)).toEqual({})
  expect(applySpec(null)(1, 2)).toEqual({})
})

test('works with unary functions', () => {
  const result = applySpec({
    v : inc,
    u : dec,
  })(1)
  const expected = {
    v : 2,
    u : 0,
  }
  expect(result).toEqual(expected)
})

test('works with binary functions', () => {
  const result = applySpec({ sum : add })(1, 2)
  expect(result).toEqual({ sum : 3 })
})

test('works with nested specs', () => {
  const result = applySpec({
    unnested : always(0),
    nested   : { sum : add },
  })(1, 2)
  const expected = {
    unnested : 0,
    nested   : { sum : 3 },
  }
  expect(result).toEqual(expected)
})

test('works with arrays of nested specs', () => {
  const result = applySpec({
    unnested : always(0),
    nested   : [ { sum : add } ],
  })(1, 2)

  expect(result).toEqual({
    unnested : 0,
    nested   : [ { sum : 3 } ],
  })
})

test('works with arrays of spec objects', () => {
  const result = applySpec([ { sum : add } ])(1, 2)

  expect(result).toEqual([ { sum : 3 } ])
})

test('works with arrays of functions', () => {
  const result = applySpec([ map(prop('a')), map(prop('b')) ])([
    {
      a : 'a1',
      b : 'b1',
    },
    {
      a : 'a2',
      b : 'b2',
    },
  ])
  const expected = [
    [ 'a1', 'a2' ],
    [ 'b1', 'b2' ],
  ]
  expect(result).toEqual(expected)
})

test('works with a spec defining a map key', () => {
  expect(applySpec({ map : prop('a') })({ a : 1 })).toEqual({ map : 1 })
})

test('cannot retains the highest arity', () => {
  const f = applySpec({
    f1 : nAry(2, T),
    f2 : nAry(5, T),
  })
  const fRamda = applySpecRamda({
    f1 : nAry(2, T),
    f2 : nAry(5, T),
  })
  expect(f).toHaveLength(0)
  expect(fRamda).toHaveLength(5)
})

test('returns a curried function', () => {
  expect(applySpec({ sum : add })(1)(2)).toEqual({ sum : 3 })
})

// Additional tests
// ============================================
test('arity', () => {
  const spec = {
    one   : x1 => x1,
    two   : (x1, x2) => x1 + x2,
    three : (
      x1, x2, x3
    ) => x1 + x2 + x3,
  }
  expect(applySpec(
    spec, 1, 2, 3
  )).toEqual({
    one   : 1,
    two   : 3,
    three : 6,
  })
})

test('arity over 5 arguments', () => {
  const spec = {
    one   : x1 => x1,
    two   : (x1, x2) => x1 + x2,
    three : (
      x1, x2, x3
    ) => x1 + x2 + x3,
    four : (
      x1, x2, x3, x4
    ) => x1 + x2 + x3 + x4,
    five : (
      x1, x2, x3, x4, x5
    ) => x1 + x2 + x3 + x4 + x5,
  }
  expect(applySpec(
    spec, 1, 2, 3, 4, 5
  )).toEqual({
    one   : 1,
    two   : 3,
    three : 6,
    four  : 10,
    five  : 15,
  })
})

test('curried', () => {
  const spec = {
    one   : x1 => x1,
    two   : (x1, x2) => x1 + x2,
    three : (
      x1, x2, x3
    ) => x1 + x2 + x3,
  }
  expect(applySpec(spec)(1)(2)(3)).toEqual({
    one   : 1,
    two   : 3,
    three : 6,
  })
})

test('curried over 5 arguments', () => {
  const spec = {
    one   : x1 => x1,
    two   : (x1, x2) => x1 + x2,
    three : (
      x1, x2, x3
    ) => x1 + x2 + x3,
    four : (
      x1, x2, x3, x4
    ) => x1 + x2 + x3 + x4,
    five : (
      x1, x2, x3, x4, x5
    ) => x1 + x2 + x3 + x4 + x5,
  }
  expect(applySpec(spec)(1)(2)(3)(4)(5)).toEqual({
    one   : 1,
    two   : 3,
    three : 6,
    four  : 10,
    five  : 15,
  })
})

test('undefined property', () => {
  const spec = { prop : path([ 'property', 'doesnt', 'exist' ]) }
  expect(applySpec(spec, {})).toEqual({ prop : undefined })
})

test('restructure json object', () => {
  const spec = {
    id          : path('user.id'),
    name        : path('user.firstname'),
    profile     : path('user.profile'),
    doesntExist : path('user.profile.doesntExist'),
    info        : { views : compose(inc, prop('views')) },
    type        : always('playa'),
  }

  const data = {
    user : {
      id        : 1337,
      firstname : 'john',
      lastname  : 'shaft',
      profile   : 'shaft69',
    },
    views : 42,
  }

  expect(applySpec(spec, data)).toEqual({
    id          : 1337,
    name        : 'john',
    profile     : 'shaft69',
    doesntExist : undefined,
    info        : { views : 43 },
    type        : 'playa',
  })
})

applyTo

Try this R.applyTo example in Rambda REPL

ascend

Try this R.ascend example in Rambda REPL

assoc

It makes a shallow clone of obj with setting or overriding the property prop with newValue.

💥 This copies and flattens prototype properties onto the new object as well. All non-primitive properties are copied by reference.

Try this R.assoc example in Rambda REPL

assocPath

assocPath<Output>(path: Path, newValue: any, obj: object): Output

It makes a shallow clone of obj with setting or overriding with newValue the property found with path.

const path = 'b.c'
const newValue = 2
const obj = { a: 1 }

R.assocPath(path, newValue, Record<string, unknown>)
// => { a : 1, b : { c : 2 }}

Try this R.assocPath example in Rambda REPL

R.assocPath source

import { cloneList } from './_internals/cloneList.js'
import { createPath } from './_internals/createPath.js'
import { isArray } from './_internals/isArray.js'
import { isIndexInteger } from './_internals/isInteger.js'
import { assocFn } from './assoc.js'
import { curry } from './curry.js'

export function assocPathFn(
  path, newValue, input
){
  const pathArrValue = createPath(path)
  if (pathArrValue.length === 0) return newValue

  const index = pathArrValue[ 0 ]
  if (pathArrValue.length > 1){
    const condition =
      typeof input !== 'object' ||
      input === null ||
      !input.hasOwnProperty(index)

    const nextInput = condition ?
      isIndexInteger(pathArrValue[ 1 ]) ?
        [] :
        {} :
      input[ index ]

    newValue = assocPathFn(
      Array.prototype.slice.call(pathArrValue, 1),
      newValue,
      nextInput
    )
  }

  if (isIndexInteger(index) && isArray(input)){
    const arr = cloneList(input)
    arr[ index ] = newValue

    return arr
  }

  return assocFn(
    index, newValue, input
  )
}

export const assocPath = curry(assocPathFn)

Tests

import { assocPathFn } from './assocPath.js'

test.only('happy', () => {
  const path = 'a.c.1'
  const input = {
    a : {
      b : 1,
      c : [ 1, 2 ],
    },
  }
  assocPathFn(
    path, 3, input
  )
  expect(input).toEqual({
    a : {
      b : 1,
      c : [ 1, 2 ],
    },
  })
})

test('string can be used as path input', () => {
  const testObj = {
    a : [ { b : 1 }, { b : 2 } ],
    d : 3,
  }
  const result1 = assocPathFn(
    [ 'a', 0, 'b' ], 10, testObj
  )
  const result2 = assocPathFn(
    'a.0.b', 10, testObj
  )

  const expected = {
    a : [ { b : 10 }, { b : 2 } ],
    d : 3,
  }
  expect(result1).toEqual(expected)
  expect(result2).toEqual(expected)
})

test('difference with ramda - doesn\'t overwrite primitive values with keys in the path', () => {
  const obj = { a : 'str' }
  const result = assocPath(
    [ 'a', 'b' ], 42, obj
  )

  expect(result).toEqual({
    a : {
      0 : 's',
      1 : 't',
      2 : 'r',
      b : 42,
    },
  })
})

test('bug', () => {
  /*
    https://github.com/selfrefactor/rambda/issues/524
  */
  const state = {}

  const withDateLike = assocPath(
    [ 'outerProp', '2020-03-10' ],
    { prop : 2 },
    state
  )
  const withNumber = assocPath(
    [ 'outerProp', '5' ], { prop : 2 }, state
  )

  const withDateLikeExpected = { outerProp : { '2020-03-10' : { prop : 2 } } }
  const withNumberExpected = { outerProp : { 5 : { prop : 2 } } }
  expect(withDateLike).toEqual(withDateLikeExpected)
  expect(withNumber).toEqual(withNumberExpected)
})

test('adds a key to an empty object', () => {
  expect(assocPath(
    [ 'a' ], 1, {}
  )).toEqual({ a : 1 })
})

test('adds a key to a non-empty object', () => {
  expect(assocPath(
    'b', 2, { a : 1 }
  )).toEqual({
    a : 1,
    b : 2,
  })
})

test('adds a nested key to a non-empty object', () => {
  expect(assocPath(
    'b.c', 2, { a : 1 }
  )).toEqual({
    a : 1,
    b : { c : 2 },
  })
})

test('adds a nested key to a nested non-empty object - curry case 1', () => {
  expect(assocPath('b.d',
    3)({
    a : 1,
    b : { c : 2 },
  })).toEqual({
    a : 1,
    b : {
      c : 2,
      d : 3,
    },
  })
})

test('adds a key to a non-empty object - curry case 1', () => {
  expect(assocPath('b', 2)({ a : 1 })).toEqual({
    a : 1,
    b : 2,
  })
})

test('adds a nested key to a non-empty object - curry case 1', () => {
  expect(assocPath('b.c', 2)({ a : 1 })).toEqual({
    a : 1,
    b : { c : 2 },
  })
})

test('adds a key to a non-empty object - curry case 2', () => {
  expect(assocPath('b')(2, { a : 1 })).toEqual({
    a : 1,
    b : 2,
  })
})

test('adds a key to a non-empty object - curry case 3', () => {
  const result = assocPath('b')(2)({ a : 1 })

  expect(result).toEqual({
    a : 1,
    b : 2,
  })
})

test('changes an existing key', () => {
  expect(assocPath(
    'a', 2, { a : 1 }
  )).toEqual({ a : 2 })
})

test('undefined is considered an empty object', () => {
  expect(assocPath(
    'a', 1, undefined
  )).toEqual({ a : 1 })
})

test('null is considered an empty object', () => {
  expect(assocPath(
    'a', 1, null
  )).toEqual({ a : 1 })
})

test('value can be null', () => {
  expect(assocPath(
    'a', null, null
  )).toEqual({ a : null })
})

test('value can be undefined', () => {
  expect(assocPath(
    'a', undefined, null
  )).toEqual({ a : undefined })
})

test('assignment is shallow', () => {
  expect(assocPath(
    'a', { b : 2 }, { a : { c : 3 } }
  )).toEqual({ a : { b : 2 } })
})

test('empty array as path', () => {
  const result = assocPath(
    [], 3, {
      a : 1,
      b : 2,
    }
  )
  expect(result).toBe(3)
})

test('happy', () => {
  const expected = { foo : { bar : { baz : 42 } } }
  const result = assocPath(
    [ 'foo', 'bar', 'baz' ], 42, { foo : null }
  )
  expect(result).toEqual(expected)
})

binary

Try this R.binary example in Rambda REPL

bind

bind<F extends AnyFunction, T>(fn: F, thisObj: T): (...args: Parameters<F>) => ReturnType<F>

Creates a function that is bound to a context.

💥 R.bind does not provide the additional argument-binding capabilities of Function.prototype.bind.

const log = R.bind(console.log, console)
const result = R.pipe(
  R.assoc('a', 2), 
  R.tap(log), 
  R.assoc('a', 3)
)({a: 1}); 
// => result - `{a: 3}`
// => console log - `{a: 2}`

Try this R.bind example in Rambda REPL

R.bind source

import { curryN } from './curryN.js'

export function bind(fn, thisObj){
  if (arguments.length === 1){
    return _thisObj => bind(fn, _thisObj)
  }

  return curryN(fn.length, (...args) => fn.apply(thisObj, args))
}

Tests

import { bind } from './bind.js'

function Foo(x){
  this.x = x
}
function add(x){
  return this.x + x
}
function Bar(x, y){
  this.x = x
  this.y = y
}
Bar.prototype = new Foo()
Bar.prototype.getX = function (){
  return 'prototype getX'
}

test('returns a function', () => {
  expect(typeof bind(add)(Foo)).toBe('function')
})

test('returns a function bound to the specified context object', () => {
  const f = new Foo(12)
  function isFoo(){
    return this instanceof Foo
  }
  const isFooBound = bind(isFoo, f)
  expect(isFoo()).toBeFalse()
  expect(isFooBound()).toBeTrue()
})

test('works with built-in types', () => {
  const abc = bind(String.prototype.toLowerCase, 'ABCDEFG')
  expect(typeof abc).toBe('function')
  expect(abc()).toBe('abcdefg')
})

test('works with user-defined types', () => {
  const f = new Foo(12)
  function getX(){
    return this.x
  }
  const getXFooBound = bind(getX, f)
  expect(getXFooBound()).toBe(12)
})

test('works with plain objects', () => {
  const pojso = { x : 100 }
  function incThis(){
    return this.x + 1
  }
  const incPojso = bind(incThis, pojso)
  expect(typeof incPojso).toBe('function')
  expect(incPojso()).toBe(101)
})

test('does not interfere with existing object methods', () => {
  const b = new Bar('a', 'b')
  function getX(){
    return this.x
  }
  const getXBarBound = bind(getX, b)
  expect(b.getX()).toBe('prototype getX')
  expect(getXBarBound()).toBe('a')
})

test('preserves arity', () => {
  const f0 = function (){
    return 0
  }
  const f1 = function (a){
    return a
  }
  const f2 = function (a, b){
    return a + b
  }
  const f3 = function (
    a, b, c
  ){
    return a + b + c
  }

  expect(bind(f0, {})).toHaveLength(0)
  expect(bind(f1, {})).toHaveLength(1)
  expect(bind(f2, {})).toHaveLength(2)
  expect(bind(f3, {})).toHaveLength(3)
})

both

both(pred1: Pred, pred2: Pred): Pred

It returns a function with input argument.

This function will return true, if both firstCondition and secondCondition return true when input is passed as their argument.

const firstCondition = x => x > 10
const secondCondition = x => x < 20
const fn = R.both(firstCondition, secondCondition)

const result = [fn(15), fn(30)]
// => [true, false]

Try this R.both example in Rambda REPL

R.both source

export function both(f, g){
  if (arguments.length === 1) return _g => both(f, _g)

  return (...input) => f(...input) && g(...input)
}

Tests

import { both } from './both.js'

const firstFn = val => val > 0
const secondFn = val => val < 10

test('with curry', () => {
  expect(both(firstFn)(secondFn)(17)).toBeFalse()
})

test('without curry', () => {
  expect(both(firstFn, secondFn)(7)).toBeTrue()
})

test('with multiple inputs', () => {
  const between = function (
    a, b, c
  ){
    return a < b && b < c
  }
  const total20 = function (
    a, b, c
  ){
    return a + b + c === 20
  }
  const fn = both(between, total20)
  expect(fn(
    5, 7, 8
  )).toBeTrue()
})

test('skip evaluation of the second expression', () => {
  let effect = 'not evaluated'
  const F = function (){
    return false
  }
  const Z = function (){
    effect = 'Z got evaluated'
  }
  both(F, Z)()

  expect(effect).toBe('not evaluated')
})

call

Try this R.call example in Rambda REPL

chain

chain<T, U>(fn: (n: T) => U[], list: T[]): U[]

The method is also known as flatMap.

const duplicate = n => [ n, n ]
const list = [ 1, 2, 3 ]

const result = chain(duplicate, list)
// => [ 1, 1, 2, 2, 3, 3 ]

Try this R.chain example in Rambda REPL

R.chain source

export function chain(fn, list){
  if (arguments.length === 1){
    return _list => chain(fn, _list)
  }

  return [].concat(...list.map(fn))
}

Tests

import { chain as chainRamda } from 'ramda'

import { chain } from './chain.js'

const duplicate = n => [ n, n ]

test('happy', () => {
  const fn = x => [ x * 2 ]
  const list = [ 1, 2, 3 ]

  const result = chain(fn, list)

  expect(result).toEqual([ 2, 4, 6 ])
})

test('maps then flattens one level', () => {
  expect(chain(duplicate, [ 1, 2, 3 ])).toEqual([ 1, 1, 2, 2, 3, 3 ])
})

test('maps then flattens one level - curry', () => {
  expect(chain(duplicate)([ 1, 2, 3 ])).toEqual([ 1, 1, 2, 2, 3, 3 ])
})

test('flattens only one level', () => {
  const nest = n => [ [ n ] ]
  expect(chain(nest, [ 1, 2, 3 ])).toEqual([ [ 1 ], [ 2 ], [ 3 ] ])
})

test('can compose', () => {
  function dec(x){
    return [ x - 1 ]
  }
  function times2(x){
    return [ x * 2 ]
  }

  const mdouble = chain(times2)
  const mdec = chain(dec)
  expect(mdec(mdouble([ 10, 20, 30 ]))).toEqual([ 19, 39, 59 ])
})

test('@types/ramda broken test', () => {
  const score = {
    maths   : 90,
    physics : 80,
  }

  const calculateTotal = score => {
    const { maths, physics } = score

    return maths + physics
  }

  const assocTotalToScore = (total, score) => ({
    ...score,
    total,
  })

  const calculateAndAssocTotalToScore = chainRamda(assocTotalToScore,
    calculateTotal)
  expect(() =>
    calculateAndAssocTotalToScore(score)).toThrowErrorMatchingInlineSnapshot('"fn(...) is not a function"')
})

clamp

Restrict a number input to be within min and max limits.

If input is bigger than max, then the result is max.

If input is smaller than min, then the result is min.

Try this R.clamp example in Rambda REPL

clone

It creates a deep copy of the input, which may contain (nested) Arrays and Objects, Numbers, Strings, Booleans and Dates.

💥 It doesn't work with very specific types, such as MongoDB's ObjectId.

Try this R.clone example in Rambda REPL

collectBy

Try this R.collectBy example in Rambda REPL

comparator

It returns a comparator function that can be used in sort method.

Try this R.comparator example in Rambda REPL

complement

It returns inverted version of origin function that accept input as argument.

The return value of inverted is the negative boolean value of origin(input).

Try this R.complement example in Rambda REPL

compose

It performs right-to-left function composition.

Try this R.compose example in Rambda REPL

composeAsync

Asynchronous version of R.compose. awaits the result of each function before passing it to the next. Returns a Promise of the result.

Try this R.composeAsync example in Rambda REPL

composeWith

Try this R.composeWith example in Rambda REPL

concat

It returns a new string or array, which is the result of merging x and y.

Try this R.concat example in Rambda REPL

cond

It takes list with conditions and returns a new function fn that expects input as argument.

This function will start evaluating the conditions in order to find the first winner(order of conditions matter).

The winner is this condition, which left side returns true when input is its argument. Then the evaluation of the right side of the winner will be the final result.

If no winner is found, then fn returns undefined.

Try this R.cond example in Rambda REPL

contains

contains<T, U>(target: T, compareTo: U): boolean

It returns true if all of target object properties are R.equal to compareTo object.

const result = R.contains({a:1}, {a:1, b:2})
// => true

Try this R.contains example in Rambda REPL

R.contains source

import { equals } from './equals.js'

export function contains(target, toCompare){
  if (arguments.length === 1){
    return _toCompare => contains(target, _toCompare)
  }
  let willReturn = true

  Object.keys(target).forEach(prop => {
    if (!willReturn) return
    if (
      toCompare[ prop ] === undefined ||
      !equals(target[ prop ], toCompare[ prop ])
    ){
      willReturn = false
    }
  })

  return willReturn
}

Tests

import { contains } from './contains.js'

const target = { a : 1 }
const compareTo = {
  a : 1,
  b : 2,
}

test('happy', () => {
  expect(contains(target, compareTo)).toBeTrue()
})

test('curried', () => {
  expect(contains({
    ...target,
    c : 3,
  },
  compareTo)).toBeFalse()
})

converge

Accepts a converging function and a list of branching functions and returns a new function. When invoked, this new function is applied to some arguments, each branching function is applied to those same arguments. The results of each branching function are passed as arguments to the converging function to produce the return value.

💥 Explanation is taken from Ramda documentation

Try this R.converge example in Rambda REPL

count

It counts how many times predicate function returns true, when supplied with iteration of list.

Try this R.count example in Rambda REPL

countBy

countBy<T extends unknown>(transformFn: (x: T) => any, list: T[]): Record<string, number>

It counts elements in a list after each instance of the input list is passed through transformFn function.

const list = [ 'a', 'A', 'b', 'B', 'c', 'C' ]

const result = countBy(R.toLower, list)
const expected = { a: 2, b: 2, c: 2 }
// => `result` is equal to `expected`

Try this R.countBy example in Rambda REPL

R.countBy source

export function countBy(fn, list){
  if (arguments.length === 1){
    return _list => countBy(fn, _list)
  }
  const willReturn = {}

  list.forEach(item => {
    const key = fn(item)
    if (!willReturn[ key ]){
      willReturn[ key ] = 1
    } else {
      willReturn[ key ]++
    }
  })

  return willReturn
}

Tests

import { countBy } from './countBy.js'

const list = [ 'a', 'A', 'b', 'B', 'c', 'C' ]

test('happy', () => {
  const result = countBy(x => x.toLowerCase(), list)
  expect(result).toEqual({
    a : 2,
    b : 2,
    c : 2,
  })
})

curry

It expects a function as input and returns its curried version.

Try this R.curry example in Rambda REPL

curryN

It returns a curried equivalent of the provided function, with the specified arity.

debounce

debounce<T, U>(fn: (input: T) => U, ms: number, immediate?: boolean): (input: T) => void

let counter = 0
const increment = () => {
  counter++
}

const debounced = R.debounce(increment, 1000)

async function fn(){
  debounced()
  await R.delay(500)
  debounced()
  await R.delay(800)
  console.log(counter) // => 0

  await R.delay(1200)
  console.log(counter) // => 1

  return counter
}
const result = await fn()
// `result` resolves to `1`

Try this R.debounce example in Rambda REPL

R.debounce source

export function debounce(
  func, ms, immediate = false
){
  let timeout

  return function (...input){
    const later = function (){
      timeout = null
      if (!immediate){
        return func.apply(null, input)
      }
    }
    const callNow = immediate && !timeout
    clearTimeout(timeout)
    timeout = setTimeout(later, ms)
    if (callNow){
      return func.apply(null, input)
    }
  }
}

Tests

import { debounce } from './debounce.js'
import { delay } from './delay.js'

test('happy', async () => {
  let counter = 0
  let aHolder

  const inc = a => {
    aHolder = a
    counter++
  }
  const incWrapped = debounce(inc, 500)

  incWrapped(1)
  expect(counter).toBe(0)

  await delay(200)

  incWrapped(2)
  expect(counter).toBe(0)

  await delay(700)
  expect(counter).toBe(1)
  expect(aHolder).toBe(2)
})

test('immediate debounce', async () => {
  let counter = 0
  const inc = () => {
    counter++
  }

  const incWrapped = debounce(
    inc, 500, true
  )
  incWrapped()
  expect(counter).toBe(1)
  await delay(200)
  incWrapped()
  expect(counter).toBe(1)
  await delay(700)
  incWrapped()
  expect(counter).toBe(2)
})

dec

It decrements a number.

Try this R.dec example in Rambda REPL

defaultTo

defaultTo<T>(defaultValue: T, input: T | null | undefined): T

It returns defaultValue, if all of inputArguments are undefined, null or NaN.

Else, it returns the first truthy inputArguments instance(from left to right).

💥 Rambda's defaultTo accept indefinite number of arguments when non curried, i.e. R.defaultTo(2, foo, bar, baz).

R.defaultTo('foo', 'bar') // => 'bar'
R.defaultTo('foo', undefined) // => 'foo'

// Important - emtpy string is not falsy value(same as Ramda)
R.defaultTo('foo', '') // => 'foo'

Try this R.defaultTo example in Rambda REPL

R.defaultTo source

function isFalsy(input){
  return (
    input === undefined || input === null || Number.isNaN(input) === true
  )
}

export function defaultTo(defaultArgument, input){
  if (arguments.length === 1){
    return _input => defaultTo(defaultArgument, _input)
  }

  return isFalsy(input) ? defaultArgument : input
}

Tests

import { defaultTo } from './defaultTo.js'

test('with undefined', () => {
  expect(defaultTo('foo')(undefined)).toBe('foo')
})

test('with null', () => {
  expect(defaultTo('foo')(null)).toBe('foo')
})

test('with NaN', () => {
  expect(defaultTo('foo')(NaN)).toBe('foo')
})

test('with empty string', () => {
  expect(defaultTo('foo', '')).toBe('')
})

test('with false', () => {
  expect(defaultTo('foo', false)).toBeFalse()
})

test('when inputArgument passes initial check', () => {
  expect(defaultTo('foo', 'bar')).toBe('bar')
})

delay

delay(ms: number): Promise<'RAMBDAX_DELAY'>

setTimeout as a promise that resolves to R.DELAY variable after ms milliseconds.

const result = R.delay(1000)
// `result` resolves to `RAMBDAX_DELAY`

Try this R.delay example in Rambda REPL

R.delay source

export const DELAY = 'RAMBDAX_DELAY'

export function delay(ms){
  return new Promise(resolve => {
    setTimeout(() => {
      resolve(DELAY)
    }, ms)
  })
}

Tests

import { DELAY, delay } from './delay.js'

test('usage with variables', async () => {
  await expect(delay(500)).resolves.toBe(DELAY)
})

descend

Try this R.descend example in Rambda REPL

difference

difference<T>(a: T[], b: T[]): T[]

It returns the uniq set of all elements in the first list a not contained in the second list b.

R.equals is used to determine equality.

const a = [ 1, 2, 3, 4 ]
const b = [ 3, 4, 5, 6 ]

const result = R.difference(a, b)
// => [ 1, 2 ]

Try this R.difference example in Rambda REPL

R.difference source

import { includes } from './includes.js'
import { uniq } from './uniq.js'

export function difference(a, b){
  if (arguments.length === 1) return _b => difference(a, _b)

  return uniq(a).filter(aInstance => !includes(aInstance, b))
}

Tests

import { difference as differenceRamda } from 'ramda'

import { difference } from './difference.js'

test('difference', () => {
  const a = [ 1, 2, 3, 4 ]
  const b = [ 3, 4, 5, 6 ]
  expect(difference(a)(b)).toEqual([ 1, 2 ])

  expect(difference([], [])).toEqual([])
})

test('difference with objects', () => {
  const a = [ { id : 1 }, { id : 2 }, { id : 3 }, { id : 4 } ]
  const b = [ { id : 3 }, { id : 4 }, { id : 5 }, { id : 6 } ]
  expect(difference(a, b)).toEqual([ { id : 1 }, { id : 2 } ])
})

test('no duplicates in first list', () => {
  const M2 = [ 1, 2, 3, 4, 1, 2, 3, 4 ]
  const N2 = [ 3, 3, 4, 4, 5, 5, 6, 6 ]
  expect(difference(M2, N2)).toEqual([ 1, 2 ])
})

test('should use R.equals', () => {
  expect(difference([ 1 ], [ 1 ])).toHaveLength(0)
  expect(differenceRamda([ NaN ], [ NaN ])).toHaveLength(0)
})

differenceWith

differenceWith<T1, T2>(
  pred: (a: T1, b: T2) => boolean,
  list1: T1[],
  list2: T2[],
): T1[]

const result = R.differenceWith(
  (a, b) => a.x === b.x,
  [{x: 1}, {x: 2}],
  [{x: 1}, {x: 3}]
)
// => [{x: 2}]

Try this R.differenceWith example in Rambda REPL

R.differenceWith source

import { curry } from './curry.js'
import { _indexOf } from './equals.js'

export function differenceWithFn(
  fn, a, b
){
  const willReturn = []
  const [ first, second ] = a.length > b.length ? [ a, b ] : [ b, a ]

  first.forEach(item => {
    const hasItem = second.some(secondItem => fn(item, secondItem))
    if (!hasItem && _indexOf(item, willReturn) === -1){
      willReturn.push(item)
    }
  })

  return willReturn
}

export const differenceWith = curry(differenceWithFn)

Tests

import { differenceWith } from './differenceWith.js'

test('happy', () => {
  const foo = [ { a : 1 }, { a : 2 }, { a : 3 } ]
  const bar = [ { a : 3 }, { a : 4 } ]
  const fn = function (r, s){
    return r.a === s.a
  }
  const result = differenceWith(
    fn, foo, bar
  )
  expect(result).toEqual([ { a : 1 }, { a : 2 } ])
})

dissoc

It returns a new object that does not contain property prop.

Try this R.dissoc example in Rambda REPL

dissocPath

Try this R.dissocPath example in Rambda REPL

divide

Try this R.divide example in Rambda REPL

drop

drop<T>(howMany: number, input: T[]): T[]

It returns howMany items dropped from beginning of list or string input.

R.drop(2, ['foo', 'bar', 'baz']) // => ['baz']
R.drop(2, 'foobar')  // => 'obar'

Try this R.drop example in Rambda REPL

R.drop source

export function drop(howManyToDrop, listOrString){
  if (arguments.length === 1) return _list => drop(howManyToDrop, _list)

  return listOrString.slice(howManyToDrop > 0 ? howManyToDrop : 0)
}

Tests

import assert from 'assert'

import { drop } from './drop.js'

test('with array', () => {
  expect(drop(2)([ 'foo', 'bar', 'baz' ])).toEqual([ 'baz' ])
  expect(drop(3, [ 'foo', 'bar', 'baz' ])).toEqual([])
  expect(drop(4, [ 'foo', 'bar', 'baz' ])).toEqual([])
})

test('with string', () => {
  expect(drop(3, 'rambda')).toBe('bda')
})

test('with non-positive count', () => {
  expect(drop(0, [ 1, 2, 3 ])).toEqual([ 1, 2, 3 ])
  expect(drop(-1, [ 1, 2, 3 ])).toEqual([ 1, 2, 3 ])
  expect(drop(-Infinity, [ 1, 2, 3 ])).toEqual([ 1, 2, 3 ])
})

test('should return copy', () => {
  const xs = [ 1, 2, 3 ]

  assert.notStrictEqual(drop(0, xs), xs)
  assert.notStrictEqual(drop(-1, xs), xs)
})

dropLast

dropLast<T>(howMany: number, input: T[]): T[]

It returns howMany items dropped from the end of list or string input.

R.dropLast(2, ['foo', 'bar', 'baz']) // => ['foo']
R.dropLast(2, 'foobar')  // => 'foob'

Try this R.dropLast example in Rambda REPL

R.dropLast source

export function dropLast(howManyToDrop, listOrString){
  if (arguments.length === 1){
    return _listOrString => dropLast(howManyToDrop, _listOrString)
  }

  return howManyToDrop > 0 ?
    listOrString.slice(0, -howManyToDrop) :
    listOrString.slice()
}

Tests

import assert from 'assert'

import { dropLast } from './dropLast.js'

test('with array', () => {
  expect(dropLast(2)([ 'foo', 'bar', 'baz' ])).toEqual([ 'foo' ])
  expect(dropLast(3, [ 'foo', 'bar', 'baz' ])).toEqual([])
  expect(dropLast(4, [ 'foo', 'bar', 'baz' ])).toEqual([])
})

test('with string', () => {
  expect(dropLast(3, 'rambda')).toBe('ram')
})

test('with non-positive count', () => {
  expect(dropLast(0, [ 1, 2, 3 ])).toEqual([ 1, 2, 3 ])
  expect(dropLast(-1, [ 1, 2, 3 ])).toEqual([ 1, 2, 3 ])
  expect(dropLast(-Infinity, [ 1, 2, 3 ])).toEqual([ 1, 2, 3 ])
})

test('should return copy', () => {
  const xs = [ 1, 2, 3 ]

  assert.notStrictEqual(dropLast(0, xs), xs)
  assert.notStrictEqual(dropLast(-1, xs), xs)
})

dropLastWhile

Try this R.dropLastWhile example in Rambda REPL

dropRepeats

dropRepeats<T>(list: T[]): T[]

It removes any successive duplicates according to R.equals.

const result = R.dropRepeats([
  1, 
  1, 
  {a: 1}, 
  {a:1}, 
  1
])
// => [1, {a: 1}, 1]

Try this R.dropRepeats example in Rambda REPL

R.dropRepeats source

import { isArray } from './_internals/isArray.js'
import { equals } from './equals.js'

export function dropRepeats(list){
  if (!isArray(list)){
    throw new Error(`${ list } is not a list`)
  }

  const toReturn = []

  list.reduce((prev, current) => {
    if (!equals(prev, current)){
      toReturn.push(current)
    }

    return current
  }, undefined)

  return toReturn
}

Tests

import { dropRepeats as dropRepeatsRamda } from 'ramda'

import { compareCombinations } from './_internals/testUtils.js'
import { add } from './add.js'
import { dropRepeats } from './dropRepeats.js'

const list = [ 1, 2, 2, 2, 3, 4, 4, 5, 5, 3, 2, 2, { a : 1 }, { a : 1 } ]
const listClean = [ 1, 2, 3, 4, 5, 3, 2, { a : 1 } ]

test('happy', () => {
  const result = dropRepeats(list)
  expect(result).toEqual(listClean)
})

const possibleLists = [
  [ add(1), async () => {}, [ 1 ], [ 1 ], [ 2 ], [ 2 ] ],
  [ add(1), add(1), add(2) ],
  [],
  1,
  /foo/g,
  Promise.resolve(1),
]

describe('brute force', () => {
  compareCombinations({
    firstInput : possibleLists,
    callback   : errorsCounters => {
      expect(errorsCounters).toMatchInlineSnapshot(`
        {
          "ERRORS_MESSAGE_MISMATCH": 0,
          "ERRORS_TYPE_MISMATCH": 0,
          "RESULTS_MISMATCH": 1,
          "SHOULD_NOT_THROW": 3,
          "SHOULD_THROW": 0,
          "TOTAL_TESTS": 6,
        }
      `)
    },
    fn      : dropRepeats,
    fnRamda : dropRepeatsRamda,
  })
})

dropRepeatsBy

Try this R.dropRepeatsBy example in Rambda REPL

dropRepeatsWith

Try this R.dropRepeatsWith example in Rambda REPL

dropWhile

Try this R.dropWhile example in Rambda REPL

either

either(firstPredicate: Pred, secondPredicate: Pred): Pred

It returns a new predicate function from firstPredicate and secondPredicate inputs.

This predicate function will return true, if any of the two input predicates return true.

const firstPredicate = x => x > 10
const secondPredicate = x => x % 2 === 0
const predicate = R.either(firstPredicate, secondPredicate)

const result = [
  predicate(15),
  predicate(8),
  predicate(7),
]
// => [true, true, false]

Try this R.either example in Rambda REPL

R.either source

export function either(firstPredicate, secondPredicate){
  if (arguments.length === 1){
    return _secondPredicate => either(firstPredicate, _secondPredicate)
  }

  return (...input) =>
    Boolean(firstPredicate(...input) || secondPredicate(...input))
}

Tests

import { either } from './either.js'

test('with multiple inputs', () => {
  const between = function (
    a, b, c
  ){
    return a < b && b < c
  }
  const total20 = function (
    a, b, c
  ){
    return a + b + c === 20
  }
  const fn = either(between, total20)
  expect(fn(
    7, 8, 5
  )).toBeTrue()
})

test('skip evaluation of the second expression', () => {
  let effect = 'not evaluated'
  const F = function (){
    return true
  }
  const Z = function (){
    effect = 'Z got evaluated'
  }
  either(F, Z)()

  expect(effect).toBe('not evaluated')
})

test('case 1', () => {
  const firstFn = val => val > 0
  const secondFn = val => val * 5 > 10

  expect(either(firstFn, secondFn)(1)).toBeTrue()
})

test('case 2', () => {
  const firstFn = val => val > 0
  const secondFn = val => val === -10
  const fn = either(firstFn)(secondFn)

  expect(fn(-10)).toBeTrue()
})

empty

Try this R.empty example in Rambda REPL

endsWith

endsWith<T extends string>(question: T, str: string): boolean

When iterable is a string, then it behaves as String.prototype.endsWith. When iterable is a list, then it uses R.equals to determine if the target list ends in the same way as the given target.

const str = 'foo-bar'
const list = [{a:1}, {a:2}, {a:3}]

const result = [
  R.endsWith('bar', str),
  R.endsWith([{a:1}, {a:2}], list)
]
// => [true, true]

Try this R.endsWith example in Rambda REPL

R.endsWith source

import { isArray } from './_internals/isArray.js'
import { equals } from './equals.js'

export function endsWith(target, iterable){
  if (arguments.length === 1) return _iterable => endsWith(target, _iterable)

  if (typeof iterable === 'string'){
    return iterable.endsWith(target)
  }
  if (!isArray(target)) return false

  const diff = iterable.length - target.length
  let correct = true
  const filtered = target.filter((x, index) => {
    if (!correct) return false
    const result = equals(x, iterable[ index + diff ])
    if (!result) correct = false

    return result
  })

  return filtered.length === target.length
}

Tests

import { endsWith as endsWithRamda } from 'ramda'

import { compareCombinations } from './_internals/testUtils.js'
import { endsWith } from './endsWith.js'

test('with string', () => {
  expect(endsWith('bar', 'foo-bar')).toBeTrue()
  expect(endsWith('baz')('foo-bar')).toBeFalse()
})

test('use R.equals with array', () => {
  const list = [ { a : 1 }, { a : 2 }, { a : 3 } ]
  expect(endsWith({ a : 3 }, list)).toBeFalse(),
  expect(endsWith([ { a : 3 } ], list)).toBeTrue()
  expect(endsWith([ { a : 2 }, { a : 3 } ], list)).toBeTrue()
  expect(endsWith(list, list)).toBeTrue()
  expect(endsWith([ { a : 1 } ], list)).toBeFalse()
})

export const possibleTargets = [
  NaN,
  [ NaN ],
  /foo/,
  [ /foo/ ],
  Promise.resolve(1),
  [ Promise.resolve(1) ],
  Error('foo'),
  [ Error('foo') ],
]

export const possibleIterables = [
  [ Promise.resolve(1), Promise.resolve(2) ],
  [ /foo/, /bar/ ],
  [ NaN ],
  [ Error('foo'), Error('bar') ],
]

describe('brute force', () => {
  compareCombinations({
    fn          : endsWith,
    fnRamda     : endsWithRamda,
    firstInput  : possibleTargets,
    secondInput : possibleIterables,
    callback    : errorsCounters => {
      expect(errorsCounters).toMatchInlineSnapshot(`
        {
          "ERRORS_MESSAGE_MISMATCH": 0,
          "ERRORS_TYPE_MISMATCH": 0,
          "RESULTS_MISMATCH": 0,
          "SHOULD_NOT_THROW": 0,
          "SHOULD_THROW": 0,
          "TOTAL_TESTS": 32,
        }
      `)
    },
  })
})

eqBy

Try this R.eqBy example in Rambda REPL

eqProps

It returns true if property prop in obj1 is equal to property prop in obj2 according to R.equals.

Try this R.eqProps example in Rambda REPL

equals

equals<T>(x: T, y: T): boolean

It deeply compares x and y and returns true if they are equal.

💥 It doesn't handle cyclical data structures and functions

R.equals(
  [1, {a:2}, [{b: 3}]],
  [1, {a:2}, [{b: 3}]]
) // => true

Try this R.equals example in Rambda REPL

R.equals source

import { isArray } from './_internals/isArray.js'
import { type } from './type.js'

export function _lastIndexOf(valueToFind, list){
  if (!isArray(list))
    throw new Error(`Cannot read property 'indexOf' of ${ list }`)

  const typeOfValue = type(valueToFind)
  if (![ 'Array', 'NaN', 'Object', 'RegExp' ].includes(typeOfValue))
    return list.lastIndexOf(valueToFind)

  const { length } = list
  let index = length
  let foundIndex = -1

  while (--index > -1 && foundIndex === -1)
    if (equals(list[ index ], valueToFind))
      foundIndex = index

  return foundIndex
}

export function _indexOf(valueToFind, list){
  if (!isArray(list))
    throw new Error(`Cannot read property 'indexOf' of ${ list }`)

  const typeOfValue = type(valueToFind)
  if (![ 'Array', 'NaN', 'Object', 'RegExp' ].includes(typeOfValue))
    return list.indexOf(valueToFind)

  let index = -1
  let foundIndex = -1
  const { length } = list

  while (++index < length && foundIndex === -1)
    if (equals(list[ index ], valueToFind))
      foundIndex = index

  return foundIndex
}

function _arrayFromIterator(iter){
  const list = []
  let next
  while (!(next = iter.next()).done)
    list.push(next.value)

  return list
}

function _compareSets(a, b){
  if (a.size !== b.size)
    return false

  const aList = _arrayFromIterator(a.values())
  const bList = _arrayFromIterator(b.values())

  const filtered = aList.filter(aInstance => _indexOf(aInstance, bList) === -1)

  return filtered.length === 0
}

function compareErrors(a, b){
  if (a.message !== b.message) return false
  if (a.toString !== b.toString) return false

  return a.toString() === b.toString()
}

function parseDate(maybeDate){
  if (!maybeDate.toDateString) return [ false ]

  return [ true, maybeDate.getTime() ]
}

function parseRegex(maybeRegex){
  if (maybeRegex.constructor !== RegExp) return [ false ]

  return [ true, maybeRegex.toString() ]
}

export function equals(a, b){
  if (arguments.length === 1) return _b => equals(a, _b)

  if (Object.is(a, b)) return true

  const aType = type(a)

  if (aType !== type(b)) return false
  if (aType === 'Function')
    return a.name === undefined ? false : a.name === b.name

  if ([ 'NaN', 'Null', 'Undefined' ].includes(aType)) return true

  if ([ 'BigInt', 'Number' ].includes(aType)){
    if (Object.is(-0, a) !== Object.is(-0, b)) return false

    return a.toString() === b.toString()
  }

  if ([ 'Boolean', 'String' ].includes(aType))
    return a.toString() === b.toString()

  if (aType === 'Array'){
    const aClone = Array.from(a)
    const bClone = Array.from(b)

    if (aClone.toString() !== bClone.toString())
      return false

    let loopArrayFlag = true
    aClone.forEach((aCloneInstance, aCloneIndex) => {
      if (loopArrayFlag)
        if (
          aCloneInstance !== bClone[ aCloneIndex ] &&
          !equals(aCloneInstance, bClone[ aCloneIndex ])
        )
          loopArrayFlag = false

    })

    return loopArrayFlag
  }

  const aRegex = parseRegex(a)
  const bRegex = parseRegex(b)

  if (aRegex[ 0 ])
    return bRegex[ 0 ] ? aRegex[ 1 ] === bRegex[ 1 ] : false
  else if (bRegex[ 0 ]) return false

  const aDate = parseDate(a)
  const bDate = parseDate(b)

  if (aDate[ 0 ])
    return bDate[ 0 ] ? aDate[ 1 ] === bDate[ 1 ] : false
  else if (bDate[ 0 ]) return false

  if (a instanceof Error){
    if (!(b instanceof Error)) return false

    return compareErrors(a, b)
  }

  if (aType === 'Set')
    return _compareSets(a, b)

  if (aType === 'Object'){
    const aKeys = Object.keys(a)

    if (aKeys.length !== Object.keys(b).length)
      return false

    let loopObjectFlag = true
    aKeys.forEach(aKeyInstance => {
      if (loopObjectFlag){
        const aValue = a[ aKeyInstance ]
        const bValue = b[ aKeyInstance ]

        if (aValue !== bValue && !equals(aValue, bValue))
          loopObjectFlag = false

      }
    })

    return loopObjectFlag
  }

  return false
}

Tests

import { equals as equalsRamda } from 'ramda'

import { compareCombinations } from './_internals/testUtils.js'
import { variousTypes } from './benchmarks/_utils.js'
import { equals } from './equals.js'

test('compare functions', () => {
  function foo(){}
  function bar(){}
  const baz = () => {}

  const expectTrue = equals(foo, foo)
  const expectFalseFirst = equals(foo, bar)
  const expectFalseSecond = equals(foo, baz)

  expect(expectTrue).toBeTrue()
  expect(expectFalseFirst).toBeFalse()
  expect(expectFalseSecond).toBeFalse()
})

test('with array of objects', () => {
  const list1 = [ { a : 1 }, [ { b : 2 } ] ]
  const list2 = [ { a : 1 }, [ { b : 2 } ] ]
  const list3 = [ { a : 1 }, [ { b : 3 } ] ]

  expect(equals(list1, list2)).toBeTrue()
  expect(equals(list1, list3)).toBeFalse()
})

test('with regex', () => {
  expect(equals(/s/, /s/)).toBeTrue()
  expect(equals(/s/, /d/)).toBeFalse()
  expect(equals(/a/gi, /a/gi)).toBeTrue()
  expect(equals(/a/gim, /a/gim)).toBeTrue()
  expect(equals(/a/gi, /a/i)).toBeFalse()
})

test('not a number', () => {
  expect(equals([ NaN ], [ NaN ])).toBeTrue()
})

test('new number', () => {
  expect(equals(new Number(0), new Number(0))).toBeTrue()
  expect(equals(new Number(0), new Number(1))).toBeFalse()
  expect(equals(new Number(1), new Number(0))).toBeFalse()
})

test('new string', () => {
  expect(equals(new String(''), new String(''))).toBeTrue()
  expect(equals(new String(''), new String('x'))).toBeFalse()
  expect(equals(new String('x'), new String(''))).toBeFalse()
  expect(equals(new String('foo'), new String('foo'))).toBeTrue()
  expect(equals(new String('foo'), new String('bar'))).toBeFalse()
  expect(equals(new String('bar'), new String('foo'))).toBeFalse()
})

test('new Boolean', () => {
  expect(equals(new Boolean(true), new Boolean(true))).toBeTrue()
  expect(equals(new Boolean(false), new Boolean(false))).toBeTrue()
  expect(equals(new Boolean(true), new Boolean(false))).toBeFalse()
  expect(equals(new Boolean(false), new Boolean(true))).toBeFalse()
})

test('new Error', () => {
  expect(equals(new Error('XXX'), {})).toBeFalse()
  expect(equals(new Error('XXX'), new TypeError('XXX'))).toBeFalse()
  expect(equals(new Error('XXX'), new Error('YYY'))).toBeFalse()
  expect(equals(new Error('XXX'), new Error('XXX'))).toBeTrue()
  expect(equals(new Error('XXX'), new TypeError('YYY'))).toBeFalse()
  expect(equals(new Error('XXX'), new Error('XXX'))).toBeTrue()
})

test('with dates', () => {
  expect(equals(new Date(0), new Date(0))).toBeTrue()
  expect(equals(new Date(1), new Date(1))).toBeTrue()
  expect(equals(new Date(0), new Date(1))).toBeFalse()
  expect(equals(new Date(1), new Date(0))).toBeFalse()
  expect(equals(new Date(0), {})).toBeFalse()
  expect(equals({}, new Date(0))).toBeFalse()
})

test('ramda spec', () => {
  expect(equals({}, {})).toBeTrue()

  expect(equals({
    a : 1,
    b : 2,
  },
  {
    a : 1,
    b : 2,
  })).toBeTrue()

  expect(equals({
    a : 2,
    b : 3,
  },
  {
    a : 2,
    b : 3,
  })).toBeTrue()

  expect(equals({
    a : 2,
    b : 3,
  },
  {
    a : 3,
    b : 3,
  })).toBeFalse()

  expect(equals({
    a : 2,
    b : 3,
    c : 1,
  },
  {
    a : 2,
    b : 3,
  })).toBeFalse()
})

test('works with boolean tuple', () => {
  expect(equals([ true, false ], [ true, false ])).toBeTrue()
  expect(equals([ true, false ], [ true, true ])).toBeFalse()
})

test('works with equal objects within array', () => {
  const objFirst = {
    a : {
      b : 1,
      c : 2,
      d : [ 1 ],
    },
  }
  const objSecond = {
    a : {
      b : 1,
      c : 2,
      d : [ 1 ],
    },
  }

  const x = [ 1, 2, objFirst, null, '', [] ]
  const y = [ 1, 2, objSecond, null, '', [] ]
  expect(equals(x, y)).toBeTrue()
})

test('works with different objects within array', () => {
  const objFirst = { a : { b : 1 } }
  const objSecond = { a : { b : 2 } }

  const x = [ 1, 2, objFirst, null, '', [] ]
  const y = [ 1, 2, objSecond, null, '', [] ]
  expect(equals(x, y)).toBeFalse()
})

test('works with undefined as second argument', () => {
  expect(equals(1, undefined)).toBeFalse()

  expect(equals(undefined, undefined)).toBeTrue()
})

test('compare sets', () => {
  const toCompareDifferent = new Set([ { a : 1 }, { a : 2 } ])
  const toCompareSame = new Set([ { a : 1 }, { a : 2 }, { a : 1 } ])
  const testSet = new Set([ { a : 1 }, { a : 2 }, { a : 1 } ])
  expect(equals(toCompareSame, testSet)).toBeTruthy()
  expect(equals(toCompareDifferent, testSet)).toBeFalsy()
  expect(equalsRamda(toCompareSame, testSet)).toBeTruthy()
  expect(equalsRamda(toCompareDifferent, testSet)).toBeFalsy()
})

test('compare simple sets', () => {
  const testSet = new Set([ '2', '3', '3', '2', '1' ])
  expect(equals(new Set([ '3', '2', '1' ]), testSet)).toBeTruthy()
  expect(equals(new Set([ '3', '2', '0' ]), testSet)).toBeFalsy()
})

test('various examples', () => {
  expect(equals([ 1, 2, 3 ])([ 1, 2, 3 ])).toBeTrue()

  expect(equals([ 1, 2, 3 ], [ 1, 2 ])).toBeFalse()

  expect(equals(1, 1)).toBeTrue()

  expect(equals(1, '1')).toBeFalse()

  expect(equals({}, {})).toBeTrue()

  expect(equals({
    a : 1,
    b : 2,
  },
  {
    a : 1,
    b : 2,
  })).toBeTrue()

  expect(equals({
    a : 1,
    b : 2,
  },
  {
    a : 1,
    b : 1,
  })).toBeFalse()

  expect(equals({
    a : 1,
    b : false,
  },
  {
    a : 1,
    b : 1,
  })).toBeFalse()

  expect(equals({
    a : 1,
    b : 2,
  },
  {
    a : 1,
    b : 2,
    c : 3,
  })).toBeFalse()

  expect(equals({
    x : {
      a : 1,
      b : 2,
    },
  },
  {
    x : {
      a : 1,
      b : 2,
      c : 3,
    },
  })).toBeFalse()

  expect(equals({
    a : 1,
    b : 2,
  },
  {
    a : 1,
    b : 3,
  })).toBeFalse()

  expect(equals({ a : { b : { c : 1 } } }, { a : { b : { c : 1 } } })).toBeTrue()

  expect(equals({ a : { b : { c : 1 } } }, { a : { b : { c : 2 } } })).toBeFalse()

  expect(equals({ a : {} }, { a : {} })).toBeTrue()

  expect(equals('', '')).toBeTrue()

  expect(equals('foo', 'foo')).toBeTrue()

  expect(equals('foo', 'bar')).toBeFalse()

  expect(equals(0, false)).toBeFalse()

  expect(equals(/\s/g, null)).toBeFalse()

  expect(equals(null, null)).toBeTrue()

  expect(equals(false)(null)).toBeFalse()
})

test('with custom functions', () => {
  function foo(){
    return 1
  }
  foo.prototype.toString = () => ''
  const result = equals(foo, foo)

  expect(result).toBeTrue()
})

test('with classes', () => {
  class Foo{}
  const foo = new Foo()
  const result = equals(foo, foo)

  expect(result).toBeTrue()
})

test('with negative zero', () => {
  expect(equals(-0, -0)).toBeTrue()
  expect(equals(-0, 0)).toBeFalse()
  expect(equals(0, 0)).toBeTrue()
  expect(equals(-0, 1)).toBeFalse()
})

test('with big int', () => {
  const a = BigInt(9007199254740991)
  const b = BigInt(9007199254740991)
  const c = BigInt(7007199254740991)
  expect(equals(a, b)).toBeTrue()
  expect(equals(a, c)).toBeFalse()
})

describe('brute force', () => {
  compareCombinations({
    callback : errorsCounters => {
      expect(errorsCounters).toMatchInlineSnapshot(`
{
  "ERRORS_MESSAGE_MISMATCH": 0,
  "ERRORS_TYPE_MISMATCH": 0,
  "RESULTS_MISMATCH": 0,
  "SHOULD_NOT_THROW": 0,
  "SHOULD_THROW": 0,
  "TOTAL_TESTS": 289,
}
`)
    },
    firstInput  : variousTypes,
    fn          : equals,
    fnRamda     : equalsRamda,
    secondInput : variousTypes,
  })
})

evolve

evolve<T, U>(rules: ((x: T) => U)[], list: T[]): U[]

It takes object or array of functions as set of rules. These rules are applied to the iterable input to produce the result.

💥 Error handling of this method differs between Ramda and Rambda. Ramda for some wrong inputs returns result and for other - it returns one of the inputs. Rambda simply throws when inputs are not correct. Full details for this mismatch are listed in source/_snapshots/evolve.spec.js.snap file.

const rules = {
  foo : add(1),
  bar : add(-1),
}
const input = {
  a   : 1,
  foo : 2,
  bar : 3,
}
const result = evolve(rules, input)
const expected = {
  a   : 1,
  foo : 3,
  bar : 2,
})
// => `result` is equal to `expected`

Try this R.evolve example in Rambda REPL

R.evolve source

import { isArray } from './_internals/isArray.js'
import { mapArray, mapObject } from './map.js'
import { type } from './type.js'

export function evolveArray(rules, list){
  return mapArray(
    (x, i) => {
      if (type(rules[ i ]) === 'Function'){
        return rules[ i ](x)
      }

      return x
    },
    list,
    true
  )
}

export function evolveObject(rules, iterable){
  return mapObject((x, prop) => {
    if (type(x) === 'Object'){
      const typeRule = type(rules[ prop ])
      if (typeRule === 'Function'){
        return rules[ prop ](x)
      }
      if (typeRule === 'Object'){
        return evolve(rules[ prop ], x)
      }

      return x
    }
    if (type(rules[ prop ]) === 'Function'){
      return rules[ prop ](x)
    }

    return x
  }, iterable)
}

export function evolve(rules, iterable){
  if (arguments.length === 1){
    return _iterable => evolve(rules, _iterable)
  }
  const rulesType = type(rules)
  const iterableType = type(iterable)

  if (iterableType !== rulesType){
    throw new Error('iterableType !== rulesType')
  }

  if (![ 'Object', 'Array' ].includes(rulesType)){
    throw new Error(`'iterable' and 'rules' are from wrong type ${ rulesType }`)
  }

  if (iterableType === 'Object'){
    return evolveObject(rules, iterable)
  }

  return evolveArray(rules, iterable)
}

Tests

import { evolve as evolveRamda } from 'ramda'

import { add } from '../rambda.js'
import { compareCombinations, compareToRamda } from './_internals/testUtils.js'
import { evolve } from './evolve.js'

test('happy', () => {
  const rules = {
    foo    : add(1),
    nested : { bar : x => Object.keys(x).length },
  }
  const input = {
    a      : 1,
    foo    : 2,
    nested : { bar : { z : 3 } },
  }
  const result = evolve(rules, input)
  expect(result).toEqual({
    a      : 1,
    foo    : 3,
    nested : { bar : 1 },
  })
})

test('nested rule is wrong', () => {
  const rules = {
    foo    : add(1),
    nested : { bar : 10 },
  }
  const input = {
    a      : 1,
    foo    : 2,
    nested : { bar : { z : 3 } },
  }
  const result = evolve(rules)(input)
  expect(result).toEqual({
    a      : 1,
    foo    : 3,
    nested : { bar : { z : 3 } },
  })
})

test('is recursive', () => {
  const rules = {
    nested : {
      second : add(-1),
      third  : add(1),
    },
  }
  const object = {
    first  : 1,
    nested : {
      second : 2,
      third  : 3,
    },
  }
  const expected = {
    first  : 1,
    nested : {
      second : 1,
      third  : 4,
    },
  }
  const result = evolve(rules, object)
  expect(result).toEqual(expected)
})

test('ignores primitive values', () => {
  const rules = {
    n : 2,
    m : 'foo',
  }
  const object = {
    n : 0,
    m : 1,
  }
  const expected = {
    n : 0,
    m : 1,
  }
  const result = evolve(rules, object)
  expect(result).toEqual(expected)
})

test('with array', () => {
  const rules = [ add(1), add(-1) ]
  const list = [ 100, 1400 ]
  const expected = [ 101, 1399 ]
  const result = evolve(rules, list)
  expect(result).toEqual(expected)
})

const rulesObject = { a : add(1) }
const rulesList = [ add(1) ]
const possibleIterables = [ null, undefined, '', 42, [], [ 1 ], { a : 1 } ]
const possibleRules = [ ...possibleIterables, rulesList, rulesObject ]

describe('brute force', () => {
  compareCombinations({
    firstInput : possibleRules,
    callback   : errorsCounters => {
      expect(errorsCounters).toMatchInlineSnapshot(`
        {
          "ERRORS_MESSAGE_MISMATCH": 0,
          "ERRORS_TYPE_MISMATCH": 4,
          "RESULTS_MISMATCH": 0,
          "SHOULD_NOT_THROW": 51,
          "SHOULD_THROW": 0,
          "TOTAL_TESTS": 63,
        }
      `)
    },
    secondInput : possibleIterables,
    fn          : evolve,
    fnRamda     : evolveRamda,
  })
})

excludes

Opposite of R.includes

R.equals is used to determine equality.

Try this R.excludes example in Rambda REPL

F

F(): boolean

F() // => false

Try this R.F example in Rambda REPL

R.F source

export function F(){
  return false
}

filter

filter<T>(predicate: Predicate<T>): (input: T[]) => T[]

It filters list or object input using a predicate function.

const list = [3, 4, 3, 2]
const listPredicate = x => x > 2

const object = {abc: 'fo', xyz: 'bar', baz: 'foo'}
const objectPredicate = (x, prop) => x.length + prop.length > 5

const result = [
  R.filter(listPredicate, list),
  R.filter(objectPredicate, object)
]
// => [ [3, 4], { xyz: 'bar', baz: 'foo'} ]

Try this R.filter example in Rambda REPL

R.filter source

import { isArray } from './_internals/isArray.js'

export function filterObject(predicate, obj){
  const willReturn = {}

  for (const prop in obj){
    if (predicate(
      obj[ prop ], prop, obj
    )){
      willReturn[ prop ] = obj[ prop ]
    }
  }

  return willReturn
}

export function filterArray(
  predicate, list, indexed = false
){
  let index = 0
  const len = list.length
  const willReturn = []

  while (index < len){
    const predicateResult = indexed ?
      predicate(list[ index ], index) :
      predicate(list[ index ])
    if (predicateResult){
      willReturn.push(list[ index ])
    }

    index++
  }

  return willReturn
}

export function filter(predicate, iterable){
  if (arguments.length === 1)
    return _iterable => filter(predicate, _iterable)
  if (!iterable){
    throw new Error('Incorrect iterable input')
  }

  if (isArray(iterable)) return filterArray(
    predicate, iterable, false
  )

  return filterObject(predicate, iterable)
}

Tests

import { filter as filterRamda } from 'ramda'

import { filter } from './filter.js'
import { T } from './T.js'

const sampleObject = {
  a : 1,
  b : 2,
  c : 3,
  d : 4,
}

test('happy', () => {
  const isEven = n => n % 2 === 0

  expect(filter(isEven, [ 1, 2, 3, 4 ])).toEqual([ 2, 4 ])
  expect(filter(isEven, {
    a : 1,
    b : 2,
    d : 3,
  })).toEqual({ b : 2 })
})

test('predicate when input is object', () => {
  const obj = {
    a : 1,
    b : 2,
  }
  const predicate = (
    val, prop, inputObject
  ) => {
    expect(inputObject).toEqual(obj)
    expect(typeof prop).toBe('string')

    return val < 2
  }
  expect(filter(predicate, obj)).toEqual({ a : 1 })
})

test('with object', () => {
  const isEven = n => n % 2 === 0
  const result = filter(isEven, sampleObject)
  const expectedResult = {
    b : 2,
    d : 4,
  }

  expect(result).toEqual(expectedResult)
})

test('bad inputs difference between Ramda and Rambda', () => {
  expect(() => filter(T, null)).toThrowWithMessage(Error,
    'Incorrect iterable input')
  expect(() => filter(T)(undefined)).toThrowWithMessage(Error,
    'Incorrect iterable input')
  expect(() => filterRamda(T, null)).toThrowWithMessage(TypeError,
    'Cannot read properties of null (reading \'fantasy-land/filter\')')
  expect(() => filterRamda(T, undefined)).toThrowWithMessage(TypeError,
    'Cannot read properties of undefined (reading \'fantasy-land/filter\')')
})

filterArray

filterArray<T>(predicate: Predicate<T>): (input: T[]) => T[]

const result = R.filterArray(
  x => x > 1,
  [1, 2, 3]
)
// => [1, 3]

Try this R.filterArray example in Rambda REPL

filterAsync

filterAsync<T>(fn: AsyncPredicate<T>, list: T[]): Promise<T[]>

Asynchronous version of R.filter

const predicate = async x => {
  await R.delay(100)
  return x % 2 === 1
}
const result = await R.filterAsync(predicate, [ 1, 2, 3 ])
// => [ 1, 3 ]

Try this R.filterAsync example in Rambda REPL

R.filterAsync source

import { isArray } from './_internals/isArray.js'
import { filter } from './filter.js'
import { mapAsync } from './mapAsync.js'

export function filterAsyncFn(predicate, listOrObject){
  return new Promise((resolve, reject) => {
    mapAsync(predicate, listOrObject)
      .then(predicateResult => {
        if (isArray(predicateResult)){
          const filtered = listOrObject.filter((_, i) => predicateResult[ i ])

          return resolve(filtered)
        }
        const filtered = filter((_, prop) => predicateResult[ prop ],
          listOrObject)

        return resolve(filtered)
      })
      .catch(reject)
  })
}

export function filterAsync(predicate, listOrObject){
  if (arguments.length === 1){
    return async _listOrObject => filterAsyncFn(predicate, _listOrObject)
  }

  return new Promise((resolve, reject) => {
    filterAsyncFn(predicate, listOrObject).then(resolve)
      .catch(reject)
  })
}

Tests

import { delay } from './delay.js'
import { filterAsync } from './filterAsync.js'

test('happy', async () => {
  const predicate = async (x, i) => {
    expect(i).toBeNumber()
    await delay(100)

    return x % 2 === 1
  }
  const result = await filterAsync(predicate)([ 1, 2, 3 ])
  expect(result).toEqual([ 1, 3 ])
})

test('with object', async () => {
  const predicate = async (x, prop) => {
    expect(prop).toBeString()
    await delay(100)

    return x % 2 === 1
  }
  const result = await filterAsync(predicate, {
    a : 1,
    b : 2,
    c : 3,
    d : 4,
    e : 5,
  })

  expect(result).toEqual({
    a : 1,
    c : 3,
    e : 5,
  })
})

filterIndexed

Same as R.filter, but it passes index/property as second argument to the predicate, when looping over arrays/objects.

filterObject

filterObject<T>(predicate: ObjectPredicate<T>): (x: Dictionary<T>) => Dictionary<T>

const obj = {a: 1, b:2}
const result = R.filterObject(
  x => x > 1,
  obj
)
// => {b: 2}

Try this R.filterObject example in Rambda REPL

find

find<T>(predicate: (x: T) => boolean, list: T[]): T | undefined

It returns the first element of list that satisfy the predicate.

If there is no such element, it returns undefined.

const predicate = x => R.type(x.foo) === 'Number'
const list = [{foo: 'bar'}, {foo: 1}]

const result = R.find(predicate, list)
// => {foo: 1}

Try this R.find example in Rambda REPL

R.find source

export function find(predicate, list){
  if (arguments.length === 1) return _list => find(predicate, _list)

  let index = 0
  const len = list.length

  while (index < len){
    const x = list[ index ]
    if (predicate(x)){
      return x
    }

    index++
  }
}

Tests

import { find } from './find.js'
import { propEq } from './propEq.js'

const list = [ { a : 1 }, { a : 2 }, { a : 3 } ]

test('happy', () => {
  const fn = propEq(2, 'a')
  expect(find(fn, list)).toEqual({ a : 2 })
})

test('with curry', () => {
  const fn = propEq(4, 'a')
  expect(find(fn)(list)).toBeUndefined()
})

test('with empty list', () => {
  expect(find(() => true, [])).toBeUndefined()
})

findAsync

Asynchronous version of R.find.

Try this R.findAsync example in Rambda REPL

findIndex

findIndex<T>(predicate: (x: T) => boolean, list: T[]): number

It returns the index of the first element of list satisfying the predicate function.

If there is no such element, then -1 is returned.

const predicate = x => R.type(x.foo) === 'Number'
const list = [{foo: 'bar'}, {foo: 1}]

const result = R.findIndex(predicate, list)
// => 1

Try this R.findIndex example in Rambda REPL

R.findIndex source

export function findIndex(predicate, list){
  if (arguments.length === 1) return _list => findIndex(predicate, _list)

  const len = list.length
  let index = -1

  while (++index < len){
    if (predicate(list[ index ])){
      return index
    }
  }

  return -1
}

Tests

import { findIndex } from './findIndex.js'
import { propEq } from './propEq.js'

const list = [ { a : 1 }, { a : 2 }, { a : 3 } ]

test('happy', () => {
  expect(findIndex(propEq(2, 'a'), list)).toBe(1)
  expect(findIndex(propEq(1, 'a'))(list)).toBe(0)
  expect(findIndex(propEq(4, 'a'))(list)).toBe(-1)
})

findLast

findLast<T>(fn: (x: T) => boolean, list: T[]): T | undefined

It returns the last element of list satisfying the predicate function.

If there is no such element, then undefined is returned.

const predicate = x => R.type(x.foo) === 'Number'
const list = [{foo: 0}, {foo: 1}]

const result = R.findLast(predicate, list)
// => {foo: 1}

Try this R.findLast example in Rambda REPL

R.findLast source

export function findLast(predicate, list){
  if (arguments.length === 1) return _list => findLast(predicate, _list)

  let index = list.length

  while (--index >= 0){
    if (predicate(list[ index ])){
      return list[ index ]
    }
  }

  return undefined
}

Tests

import { findLast } from './findLast.js'

test('happy', () => {
  const result = findLast(x => x > 1, [ 1, 1, 1, 2, 3, 4, 1 ])
  expect(result).toBe(4)

  expect(findLast(x => x === 0, [ 0, 1, 1, 2, 3, 4, 1 ])).toBe(0)
})

test('with curry', () => {
  expect(findLast(x => x > 1)([ 1, 1, 1, 2, 3, 4, 1 ])).toBe(4)
})

const obj1 = { x : 100 }
const obj2 = { x : 200 }
const a = [ 11, 10, 9, 'cow', obj1, 8, 7, 100, 200, 300, obj2, 4, 3, 2, 1, 0 ]
const even = function (x){
  return x % 2 === 0
}
const gt100 = function (x){
  return x > 100
}
const isStr = function (x){
  return typeof x === 'string'
}
const xGt100 = function (o){
  return o && o.x > 100
}

test('ramda 1', () => {
  expect(findLast(even, a)).toBe(0)
  expect(findLast(gt100, a)).toBe(300)
  expect(findLast(isStr, a)).toBe('cow')
  expect(findLast(xGt100, a)).toEqual(obj2)
})

test('ramda 2', () => {
  expect(findLast(even, [ 'zing' ])).toBeUndefined()
})

test('ramda 3', () => {
  expect(findLast(even, [ 2, 3, 5 ])).toBe(2)
})

test('ramda 4', () => {
  expect(findLast(even, [])).toBeUndefined()
})

findLastIndex

findLastIndex<T>(predicate: (x: T) => boolean, list: T[]): number

It returns the index of the last element of list satisfying the predicate function.

If there is no such element, then -1 is returned.

const predicate = x => R.type(x.foo) === 'Number'
const list = [{foo: 0}, {foo: 1}]

const result = R.findLastIndex(predicate, list)
// => 1

Try this R.findLastIndex example in Rambda REPL

R.findLastIndex source

export function findLastIndex(fn, list){
  if (arguments.length === 1) return _list => findLastIndex(fn, _list)

  let index = list.length

  while (--index >= 0){
    if (fn(list[ index ])){
      return index
    }
  }

  return -1
}

Tests

import { findLastIndex } from './findLastIndex.js'

test('happy', () => {
  const result = findLastIndex(x => x > 1, [ 1, 1, 1, 2, 3, 4, 1 ])

  expect(result).toBe(5)

  expect(findLastIndex(x => x === 0, [ 0, 1, 1, 2, 3, 4, 1 ])).toBe(0)
})

test('with curry', () => {
  expect(findLastIndex(x => x > 1)([ 1, 1, 1, 2, 3, 4, 1 ])).toBe(5)
})

const obj1 = { x : 100 }
const obj2 = { x : 200 }
const a = [ 11, 10, 9, 'cow', obj1, 8, 7, 100, 200, 300, obj2, 4, 3, 2, 1, 0 ]
const even = function (x){
  return x % 2 === 0
}
const gt100 = function (x){
  return x > 100
}
const isStr = function (x){
  return typeof x === 'string'
}
const xGt100 = function (o){
  return o && o.x > 100
}

test('ramda 1', () => {
  expect(findLastIndex(even, a)).toBe(15)
  expect(findLastIndex(gt100, a)).toBe(9)
  expect(findLastIndex(isStr, a)).toBe(3)
  expect(findLastIndex(xGt100, a)).toBe(10)
})

test('ramda 2', () => {
  expect(findLastIndex(even, [ 'zing' ])).toBe(-1)
})

test('ramda 3', () => {
  expect(findLastIndex(even, [ 2, 3, 5 ])).toBe(0)
})

test('ramda 4', () => {
  expect(findLastIndex(even, [])).toBe(-1)
})

flatten

flatten<T>(list: any[]): T[]

It deeply flattens an array.

const result = R.flatten([
  1, 
  2, 
  [3, 30, [300]], 
  [4]
])
// => [ 1, 2, 3, 30, 300, 4 ]

Try this R.flatten example in Rambda REPL

R.flatten source

import { isArray } from './_internals/isArray.js'

export function flatten(list, input){
  const willReturn = input === undefined ? [] : input

  for (let i = 0; i < list.length; i++){
    if (isArray(list[ i ])){
      flatten(list[ i ], willReturn)
    } else {
      willReturn.push(list[ i ])
    }
  }

  return willReturn
}

Tests

import { flatten } from './flatten.js'

test('happy', () => {
  expect(flatten([ 1, 2, 3, [ [ [ [ [ 4 ] ] ] ] ] ])).toEqual([ 1, 2, 3, 4 ])

  expect(flatten([ 1, [ 2, [ [ 3 ] ] ], [ 4 ] ])).toEqual([ 1, 2, 3, 4 ])

  expect(flatten([ 1, [ 2, [ [ [ 3 ] ] ] ], [ 4 ] ])).toEqual([ 1, 2, 3, 4 ])

  expect(flatten([ 1, 2, [ 3, 4 ], 5, [ 6, [ 7, 8, [ 9, [ 10, 11 ], 12 ] ] ] ])).toEqual([ 1, 2, 3, 4, 5, 6, 7, 8, 9, 10, 11, 12 ])
})

test('readme example', () => {
  const result = flatten([ 1, 2, [ 3, 30, [ 300 ] ], [ 4 ] ])
  expect(result).toEqual([ 1, 2, 3, 30, 300, 4 ])
})

flip

It returns function which calls fn with exchanged first and second argument.

💥 Rambda's flip will throw if the arity of the input function is greater or equal to 5.

Try this R.flip example in Rambda REPL

forEach

forEach<T>(fn: Iterator<T, void>, list: T[]): T[]

It applies iterable function over all members of list and returns list.

💥 It works with objects, unlike Ramda.

const sideEffect = {}
const result = R.forEach(
  x => sideEffect[`foo${x}`] = x
)([1, 2])

sideEffect // => {foo1: 1, foo2: 2}
result // => [1, 2]

Try this R.forEach example in Rambda REPL

R.forEach source

import { isArray } from './_internals/isArray.js'
import { forEachObjIndexedFn } from './forEachObjIndexed.js'

export function forEach(fn, iterable){
  if (arguments.length === 1) return _list => forEach(fn, _list)
  if (iterable === undefined) return

  if (isArray(iterable)){
    let index = 0
    const len = iterable.length

    while (index < len){
      fn(iterable[ index ])
      index++
    }
  } else return forEachObjIndexedFn(fn, iterable)

  return iterable
}

Tests

import { forEach } from './forEach.js'
import { type } from './type.js'

test('happy', () => {
  const sideEffect = {}
  forEach(x => sideEffect[ `foo${ x }` ] = x + 10)([ 1, 2 ])

  expect(sideEffect).toEqual({
    foo1 : 11,
    foo2 : 12,
  })
})

test('iterate over object', () => {
  const obj = {
    a : 1,
    b : [ 1, 2 ],
    c : { d : 7 },
    f : 'foo',
  }
  const result = {}
  const returned = forEach((
    val, prop, inputObj
  ) => {
    expect(type(inputObj)).toBe('Object')
    result[ prop ] = `${ prop }-${ type(val) }`
  })(obj)

  const expected = {
    a : 'a-Number',
    b : 'b-Array',
    c : 'c-Object',
    f : 'f-String',
  }

  expect(result).toEqual(expected)
  expect(returned).toEqual(obj)
})

test('with empty list', () => {
  const list = []
  const result = forEach(x => x * x)(list)

  expect(result).toEqual(list)
})

test('with wrong input', () => {
  const list = undefined
  const result = forEach(x => x * x)(list)

  expect(result).toBeUndefined()
})

test('returns the input', () => {
  const list = [ 1, 2, 3 ]
  const result = forEach(x => x * x)(list)

  expect(result).toEqual(list)
})

forEachIndexed

forEachObjIndexed

fromPairs

It transforms a listOfPairs to an object.

Try this R.fromPairs example in Rambda REPL

getter

getter<T>(keyOrKeys: string | string[] | undefined): T

The set of methods R.setter, R.getter and R.reset allow different parts of your logic to access communicate indirectly via shared cache object.

Usually these methods show that you might need to refactor to classes. Still, they can be helpful meanwhile.

R.getter: It provides access to the cache object. If undefined is used as a key, this method will return the whole cache object. If string is passed, then it will return cache value for this key. If array of string is passed, then it assume that this is array of keys and it will return the corresponding cache values for these keys.

R.setter: It allows cache object's keys to be changed. You can either set individual key-value pairs with R.setter(key, value) or you pass directly object, which will be merged with the cache object.

R.reset: It resets the cache object.

R.setter('foo','bar')
R.setter('a', 1)
R.getter(['foo','a']) // => {foo: 'bar', a: 1}

R.setter('a', 2)
R.getter('a') // => 2
R.reset()
R.getter('a') // => undefined

Try this R.getter example in Rambda REPL

R.getter source

import { mergeRight } from './mergeRight.js'
import { pick } from './pick.js'
import { type } from './type.js'

let holder = {}

/**
 * Pass string to get value
 * Pass array to get object of values
 * Pass undefined to get all data
 */
export function getter(key){
  const typeKey = type(key)

  if (typeKey === 'String') return holder[ key ]

  if (typeKey === 'Array') return pick(key, holder)

  return holder
}

export function setter(maybeKey, maybeValue){
  const typeKey = type(maybeKey)
  const typeValue = type(maybeValue)

  if (typeKey === 'String'){
    if (typeValue === 'Function'){
      return holder[ maybeKey ] = maybeValue(holder[ maybeKey ])
    }

    return holder[ maybeKey ] = maybeValue
  }

  if (typeKey !== 'Object') return

  holder = mergeRight(holder, maybeKey)
}

export function reset(){
  holder = {}
}

Tests

import { add } from './add.js'
import { getter, reset, setter } from './getter.js'

afterEach(() => {
  reset()
})

test('happy', () => {
  const key = 'foo'
  setter(key, 1)

  expect(getter(key)).toBe(1)
})

test('docs example', () => {
  setter('foo', 'bar')
  setter('a', 1)
  expect(getter([ 'foo', 'a' ])).toEqual({
    foo : 'bar',
    a   : 1,
  })

  setter('a', 2)
  expect(getter('a')).toBe(2)
  reset()
  expect(getter('a')).toBeUndefined()
})

test('when array is key in getter', () => {
  setter({
    a : 1,
    b : 2,
    c : 3,
  })

  expect(getter([ 'a', 'b' ])).toEqual({
    a : 1,
    b : 2,
  })
})

test('getter with undefined as key returns all', () => {
  const data = {
    a : 1,
    b : 2,
    c : 3,
  }

  setter(data)

  expect(getter()).toEqual(data)
})

test('function as setter value', () => {
  const data = {
    a : 1,
    b : 2,
    c : 3,
  }

  setter(data)
  setter('a', add(10))

  expect(getter()).toEqual({
    a : 11,
    b : 2,
    c : 3,
  })
})

test('setter fallbacks to undefined', () => {
  expect(setter()).toBeUndefined
})

glue

glue(input: string, glueString?: string): string

It transforms multiline string to single line by gluing together the separate lines with the glueString and removing the empty spaces. By default glueString is equal to single space, so if that is what you need, then you can just pass a single argument.

const result = R.glue(`
  foo
  bar
  baz
`)
// => 'foo bar baz'

Try this R.glue example in Rambda REPL

R.glue source

export function glue(input, glueChar){
  return input
    .split('\n')
    .filter(x => x.trim().length > 0)
    .map(x => x.trim())
    .join(glueChar === undefined ? ' ' : glueChar)
}

Tests

import { glue } from './glue.js'

test('empty string as a glue', () => {
  const result = glue(`
    foo
    bar
    baz
  `,
  '')

  const expectedResult = 'foobarbaz'

  expect(result).toBe(expectedResult)
})

test('case 0', () => {
  const zero = 'node node_modules/jest'
  const first = '--runInBand'
  const last = '-- src/a.spec.js'
  const flag = false
  const result = glue(`
    ${ zero }
    ${ first }
    ${ flag ? '--env=node' : '' }
    ${ last }
  `)

  const expectedResult = `${ zero } ${ first } ${ last }`

  expect(result).toBe(expectedResult)
})

test('case 1', () => {
  const zero = 'node node_modules/jest'
  const first = '--runInBand'
  const last = '-- src/a.spec.js'
  const flag = true
  const result = glue(`
    ${ zero }
    ${ first }
    ${ flag ? '--env=node' : '' }
    ${ last }
  `)

  const expectedResult = `${ zero } ${ first } --env=node ${ last }`

  expect(result).toBe(expectedResult)
})

test('case 2', () => {
  const first = '--runInBand'
  const result = glue(`
    zero
    ${ first }
    last
  `)
  const expectedResult = `zero ${ first } last`

  expect(result).toBe(expectedResult)
})

test('case 3', () => {
  const result = glue(`
    foo
    bar
    baz
  `)

  const expectedResult = 'foo bar baz'

  expect(result).toBe(expectedResult)
})

test('with glue', () => {
  const result = glue(`
    foo
    bar
    baz
  `,
  '==')

  const expectedResult = 'foo==bar==baz'

  expect(result).toBe(expectedResult)
})

groupBy

It splits list according to a provided groupFn function and returns an object.

Try this R.groupBy example in Rambda REPL

groupWith

It returns separated version of list or string input, where separation is done with equality compareFn function.

Try this R.groupWith example in Rambda REPL

gt

Try this R.gt example in Rambda REPL

gte

Try this R.gte example in Rambda REPL

has

has<T>(prop: string, obj: T): boolean

It returns true if obj has property prop.

const obj = {a: 1}

const result = [
  R.has('a', Record<string, unknown>),
  R.has('b', Record<string, unknown>)
]
// => [true, false]

Try this R.has example in Rambda REPL

R.has source

export function has(prop, obj){
  if (arguments.length === 1) return _obj => has(prop, _obj)

  if (!obj) return false

  return obj.hasOwnProperty(prop)
}

Tests

import { has } from './has.js'

test('happy', () => {
  expect(has('a')({ a : 1 })).toBeTrue()
  expect(has('b', { a : 1 })).toBeFalse()
})

test('with non-object', () => {
  expect(has('a', undefined)).toBeFalse()
  expect(has('a', null)).toBeFalse()
  expect(has('a', true)).toBeFalse()
  expect(has('a', '')).toBeFalse()
  expect(has('a', /a/)).toBeFalse()
})

hasIn

Try this R.hasIn example in Rambda REPL

hasPath

hasPath<T>(
  path: string | string[],
  input: object
): boolean

It will return true, if input object has truthy path(calculated with R.path).

const path = 'a.b'
const pathAsArray = ['a', 'b']
const obj = {a: {b: []}}

const result = [
  R.hasPath(path, Record<string, unknown>),
  R.hasPath(pathAsArray, Record<string, unknown>),
  R.hasPath('a.c', Record<string, unknown>),
]
// => [true, true, false]

Try this R.hasPath example in Rambda REPL

R.hasPath source

import { path } from './path.js'

export function hasPath(pathInput, obj){
  if (arguments.length === 1){
    return objHolder => hasPath(pathInput, objHolder)
  }

  return path(pathInput, obj) !== undefined
}

Tests

import { hasPath } from './hasPath.js'

test('when true', () => {
  const path = 'a.b'
  const obj = { a : { b : [] } }

  const result = hasPath(path)(obj)
  const expectedResult = true

  expect(result).toEqual(expectedResult)
})

test('when false', () => {
  const path = 'a.b'
  const obj = {}

  const result = hasPath(path, obj)
  const expectedResult = false

  expect(result).toEqual(expectedResult)
})

head

head(str: string): string

It returns the first element of list or string input.

const result = [
  R.head([1, 2, 3]),
  R.head('foo') 
]
// => [1, 'f']

Try this R.head example in Rambda REPL

R.head source

export function head(listOrString){
  if (typeof listOrString === 'string') return listOrString[ 0 ] || ''

  return listOrString[ 0 ]
}

Tests

import { head } from './head.js'

test('head', () => {
  expect(head([ 'fi', 'fo', 'fum' ])).toBe('fi')
  expect(head([])).toBeUndefined()
  expect(head('foo')).toBe('f')
  expect(head('')).toBe('')
})

identical

It returns true if its arguments a and b are identical.

Otherwise, it returns false.

💥 Values are identical if they reference the same memory. NaN is identical to NaN; 0 and -0 are not identical.

Try this R.identical example in Rambda REPL

identity

identity<T>(input: T): T

It just passes back the supplied input argument.

💥 Logic

R.identity(7) // => 7

Try this R.identity example in Rambda REPL

R.identity source

export function identity(x){
  return x
}

Tests

import { identity } from './identity.js'

test('happy', () => {
  expect(identity(7)).toBe(7)
  expect(identity(true)).toBeTrue()
  expect(identity({ a : 1 })).toEqual({ a : 1 })
})

ifElse

ifElse<T, TFiltered extends T, TOnTrueResult, TOnFalseResult>(
  pred: (a: T) => a is TFiltered,
  onTrue: (a: TFiltered) => TOnTrueResult,
  onFalse: (a: Exclude<T, TFiltered>) => TOnFalseResult,
): (a: T) => TOnTrueResult | TOnFalseResult

It expects condition, onTrue and onFalse functions as inputs and it returns a new function with example name of fn.

When fn`` is called with inputargument, it will return eitheronTrue(input)oronFalse(input)depending oncondition(input)` evaluation.

const fn = R.ifElse(
 x => x>10,
 x => x*2,
 x => x*10
)

const result = [ fn(8), fn(18) ]
// => [80, 36]

Try this R.ifElse example in Rambda REPL

R.ifElse source

import { curry } from './curry.js'

function ifElseFn(
  condition, onTrue, onFalse
){
  return (...input) => {
    const conditionResult =
      typeof condition === 'boolean' ? condition : condition(...input)

    if (conditionResult === true){
      return onTrue(...input)
    }

    return onFalse(...input)
  }
}

export const ifElse = curry(ifElseFn)

Tests

import { always } from './always.js'
import { has } from './has.js'
import { identity } from './identity.js'
import { ifElse } from './ifElse.js'
import { prop } from './prop.js'

const condition = has('foo')
const v = function (a){
  return typeof a === 'number'
}
const t = function (a){
  return a + 1
}
const ifFn = x => prop('foo', x).length
const elseFn = () => false

test('happy', () => {
  const fn = ifElse(condition, ifFn)(elseFn)

  expect(fn({ foo : 'bar' })).toBe(3)
  expect(fn({ fo : 'bar' })).toBeFalse()
})

test('ramda spec', () => {
  const ifIsNumber = ifElse(v)
  expect(ifIsNumber(t, identity)(15)).toBe(16)
  expect(ifIsNumber(t, identity)('hello')).toBe('hello')
})

test('pass all arguments', () => {
  const identity = function (a){
    return a
  }
  const v = function (){
    return true
  }
  const onTrue = function (a, b){
    expect(a).toBe(123)
    expect(b).toBe('abc')
  }
  ifElse(
    v, onTrue, identity
  )(123, 'abc')
})

test('accept constant as condition', () => {
  const fn = ifElse(true)(always(true))(always(false))

  expect(fn()).toBeTrue()
})

test('accept constant as condition - case 2', () => {
  const fn = ifElse(
    false, always(true), always(false)
  )

  expect(fn()).toBeFalse()
})

test('curry 1', () => {
  const fn = ifElse(condition, ifFn)(elseFn)

  expect(fn({ foo : 'bar' })).toBe(3)
  expect(fn({ fo : 'bar' })).toBeFalse()
})

test('curry 2', () => {
  const fn = ifElse(condition)(ifFn)(elseFn)

  expect(fn({ foo : 'bar' })).toBe(3)
  expect(fn({ fo : 'bar' })).toBeFalse()
})

test('simple arity of 1', () => {
  const condition = x => x > 5
  const onTrue = x => x + 1
  const onFalse = x => x + 10
  const result = ifElse(
    condition, onTrue, onFalse
  )(1)
  expect(result).toBe(11)
})

test('simple arity of 2', () => {
  const condition = (x, y) => x + y > 5
  const onTrue = (x, y) => x + y + 1
  const onFalse = (x, y) => x + y + 10
  const result = ifElse(
    condition, onTrue, onFalse
  )(1, 10)
  expect(result).toBe(12)
})

ifElseAsync

ifElseAsync<T, U>(
  condition: (x: T) => Promise<boolean>, 
  onTrue: (x: T) => U, 
  onFalse: (x: T) => U, 
  ): (x: T) => Promise<U>

Asynchronous version of R.ifElse. Any of condition, ifFn and elseFn can be either asynchronous or synchronous function.

const condition = async x => {
  await R.delay(100)
  return x > 1
}
const ifFn = async x => {
  await R.delay(100)
  return x + 1
}
const elseFn = async x => {
  await R.delay(100)
  return x - 1
}

const result = await R.ifElseAsync(
  condition,
  ifFn,
  elseFn  
)(1)
// => 0

Try this R.ifElseAsync example in Rambda REPL

R.ifElseAsync source

function createThenable(fn){
  return async function (...input){
    return fn(...input)
  }
}

export function ifElseAsync(
  condition, ifFn, elseFn
){
  return (...inputs) =>
    new Promise((resolve, reject) => {
      const conditionPromise = createThenable(condition)
      const ifFnPromise = createThenable(ifFn)
      const elseFnPromise = createThenable(elseFn)

      conditionPromise(...inputs)
        .then(conditionResult => {
          const promised =
            conditionResult === true ? ifFnPromise : elseFnPromise

          promised(...inputs)
            .then(resolve)
            .catch(reject)
        })
        .catch(reject)
    })
}

Tests

import { delay } from './delay.js'
import { ifElseAsync } from './ifElseAsync.js'

test('arity of 1 - condition is async', async () => {
  const condition = async x => {
    await delay(100)

    return x > 4
  }
  const whenTrue = x => x + 1
  const whenFalse = x => x + 10
  const fn = ifElseAsync(
    condition, whenTrue, whenFalse
  )
  const result = await Promise.all([ fn(5), fn(1) ])
  expect(result).toEqual([ 6, 11 ])
})

test('arity of 1 - condition is sync', async () => {
  const condition = x => x > 4
  const whenTrue = async x => {
    await delay(100)

    return x + 1
  }
  const whenFalse = async x => {
    await delay(100)

    return x + 10
  }
  const fn = ifElseAsync(
    condition, whenTrue, whenFalse
  )
  const result = await Promise.all([ fn(5), fn(1) ])
  expect(result).toEqual([ 6, 11 ])
})

test('arity of 1 - all inputs are async', async () => {
  const condition = async x => {
    await delay(100)

    return x > 4
  }
  const whenTrue = async x => {
    await delay(100)

    return x + 1
  }
  const whenFalse = async x => {
    await delay(100)

    return x + 10
  }
  const fn = ifElseAsync(
    condition, whenTrue, whenFalse
  )
  const result = await Promise.all([ fn(5), fn(1) ])
  expect(result).toEqual([ 6, 11 ])
})

test('arity of 2 - condition is async', async () => {
  const condition = async (x, y) => {
    await delay(100)

    return x + y > 4
  }
  const whenTrue = (x, y) => x + y + 1
  const whenFalse = (x, y) => x + y + 10
  const fn = ifElseAsync(
    condition, whenTrue, whenFalse
  )
  const result = await Promise.all([ fn(14, 20), fn(1, 3) ])
  expect(result).toEqual([ 35, 14 ])
})

test('arity of 2 - condition is sync', async () => {
  const condition = (x, y) => x + y > 4
  const whenTrue = async (x, y) => {
    await delay(100)

    return x + y + 1
  }
  const whenFalse = async (x, y) => {
    await delay(100)

    return x + y + 10
  }
  const fn = ifElseAsync(
    condition, whenTrue, whenFalse
  )
  const result = await Promise.all([ fn(14, 20), fn(1, 3) ])
  expect(result).toEqual([ 35, 14 ])
})

test('arity of 2 - all inputs are async', async () => {
  const condition = async (x, y) => {
    await delay(100)

    return x + y > 4
  }
  const whenTrue = async (x, y) => {
    await delay(100)

    return x + y + 1
  }
  const whenFalse = async (x, y) => {
    await delay(100)

    return x + y + 10
  }
  const fn = ifElseAsync(
    condition, whenTrue, whenFalse
  )
  const result = await Promise.all([ fn(14, 20), fn(1, 3) ])
  expect(result).toEqual([ 35, 14 ])
})

inc

It increments a number.

Try this R.inc example in Rambda REPL

includes

includes<T extends string>(valueToFind: T, input: string): boolean

If input is string, then this method work as native String.includes.

If input is array, then R.equals is used to define if valueToFind belongs to the list.

const result = [
  R.includes('oo', 'foo'),
  R.includes({a: 1}, [{a: 1}])
]
// => [true, true ]

Try this R.includes example in Rambda REPL

R.includes source

import { isArray } from './_internals/isArray.js'
import { _indexOf } from './equals.js'

export function includes(valueToFind, iterable){
  if (arguments.length === 1)
    return _iterable => includes(valueToFind, _iterable)
  if (typeof iterable === 'string'){
    return iterable.includes(valueToFind)
  }
  if (!iterable){
    throw new TypeError(`Cannot read property \'indexOf\' of ${ iterable }`)
  }
  if (!isArray(iterable)) return false

  return _indexOf(valueToFind, iterable) > -1
}

Tests

import { includes as includesRamda } from 'ramda'

import { includes } from './includes.js'

test('with string as iterable', () => {
  const str = 'foo bar'

  expect(includes('bar')(str)).toBeTrue()
  expect(includesRamda('bar')(str)).toBeTrue()
  expect(includes('never', str)).toBeFalse()
  expect(includesRamda('never', str)).toBeFalse()
})

test('with array as iterable', () => {
  const arr = [ 1, 2, 3 ]

  expect(includes(2)(arr)).toBeTrue()
  expect(includesRamda(2)(arr)).toBeTrue()

  expect(includes(4, arr)).toBeFalse()
  expect(includesRamda(4, arr)).toBeFalse()
})

test('with list of objects as iterable', () => {
  const arr = [ { a : 1 }, { b : 2 }, { c : 3 } ]

  expect(includes({ c : 3 }, arr)).toBeTrue()
  expect(includesRamda({ c : 3 }, arr)).toBeTrue()
})

test('with NaN', () => {
  const result = includes(NaN, [ NaN ])
  const ramdaResult = includesRamda(NaN, [ NaN ])
  expect(result).toBeTrue()
  expect(ramdaResult).toBeTrue()
})

test('with wrong input that does not throw', () => {
  const result = includes(1, /foo/g)
  const ramdaResult = includesRamda(1, /foo/g)
  expect(result).toBeFalse()
  expect(ramdaResult).toBeFalse()
})

test('throws on wrong input - match ramda behaviour', () => {
  expect(() => includes(2, null)).toThrowWithMessage(TypeError,
    'Cannot read property \'indexOf\' of null')
  expect(() => includesRamda(2, null)).toThrowWithMessage(TypeError,
    'Cannot read properties of null (reading \'indexOf\')')
  expect(() => includes(2, undefined)).toThrowWithMessage(TypeError,
    'Cannot read property \'indexOf\' of undefined')
  expect(() => includesRamda(2, undefined)).toThrowWithMessage(TypeError,
    'Cannot read properties of undefined (reading \'indexOf\')')
})

indexBy

It generates object with properties provided by condition and values provided by list array.

If condition is a function, then all list members are passed through it.

If condition is a string, then all list members are passed through R.path(condition).

Try this R.indexBy example in Rambda REPL

indexOf

It returns the index of the first element of list equals to valueToFind.

If there is no such element, it returns -1.

💥 It uses R.equals for list of objects/arrays or native indexOf for any other case.

Try this R.indexOf example in Rambda REPL

init

init<T extends unknown[]>(input: T): T extends readonly [...infer U, any] ? U : [...T]

It returns all but the last element of list or string input.

const result = [
  R.init([1, 2, 3]) , 
  R.init('foo')  // => 'fo'
]
// => [[1, 2], 'fo']

Try this R.init example in Rambda REPL

R.init source

import baseSlice from './_internals/baseSlice.js'

export function init(listOrString){
  if (typeof listOrString === 'string') return listOrString.slice(0, -1)

  return listOrString.length ?
    baseSlice(
      listOrString, 0, -1
    ) :
    []
}

Tests

import { init } from './init.js'

test('with array', () => {
  expect(init([ 1, 2, 3 ])).toEqual([ 1, 2 ])
  expect(init([ 1, 2 ])).toEqual([ 1 ])
  expect(init([ 1 ])).toEqual([])
  expect(init([])).toEqual([])
  expect(init([])).toEqual([])
  expect(init([ 1 ])).toEqual([])
})

test('with string', () => {
  expect(init('foo')).toBe('fo')
  expect(init('f')).toBe('')
  expect(init('')).toBe('')
})

innerJoin

It returns a new list by applying a predicate function to all elements of list1 and list2 and keeping only these elements where predicate returns true.

Try this R.innerJoin example in Rambda REPL

insert

Try this R.insert example in Rambda REPL

insertAll

Try this R.insertAll example in Rambda REPL

interpolate

interpolate(inputWithTags: string, templateArguments: object): string

It generates a new string from inputWithTags by replacing all {{x}} occurrences with values provided by templateArguments.

const inputWithTags = 'foo is {{bar}} even {{a}} more'
const templateArguments = {"bar":"BAR", a: 1}

const result = R.interpolate(inputWithTags, templateArguments)
const expected = 'foo is BAR even 1 more'
// => `result` is equal to `expected`

Try this R.interpolate example in Rambda REPL

R.interpolate source

const getOccurrences = input => input.match(/{{\s*.+?\s*}}/g)

const getOccurrenceProp = occurrence =>
  occurrence.replace(/{{\s*|\s*}}/g, '')

const replace = ({ inputHolder, prop, replacer }) => {
  const regexBase = `{{${ prop }}}`
  const regex = new RegExp(regexBase, 'g')

  return inputHolder.replace(regex, replacer)
}

export function interpolate(input, templateInput){
  if (arguments.length === 1){
    return _templateInput => interpolate(input, _templateInput)
  }

  const occurrences = getOccurrences(input)
  if (occurrences === null) return input
  let inputHolder = input

  for (const occurrence of occurrences){
    const prop = getOccurrenceProp(occurrence)

    inputHolder = replace({
      inputHolder,
      prop,
      replacer : templateInput[ prop ],
    })
  }

  return inputHolder
}

Tests

import { interpolate } from './interpolate.js'

test('within bracets', () => {
  const input = 'foo is { {{bar}} } even {{a}} more'
  const templateInput = {
    bar : 'BAR',
    a   : 1,
  }

  const result = interpolate(input, templateInput)
  const expectedResult = 'foo is { BAR } even 1 more'

  expect(result).toEqual(expectedResult)
})

test('happy', () => {
  const input = 'foo is {{bar}} even {{a}} more'
  const templateInput = {
    bar : 'BAR',
    a   : 1,
  }

  const result = interpolate(input, templateInput)
  const expectedResult = 'foo is BAR even 1 more'

  expect(result).toEqual(expectedResult)
})

test('no interpolation + curry', () => {
  const input = 'foo is bar even more'
  const templateInput = { bar : 'BAR' }

  const result = interpolate(input)(templateInput)
  const expectedResult = 'foo is bar even more'

  expect(result).toEqual(expectedResult)
})

test('with missing template input', () => {
  const input = 'foo is {{bar}} even {{a}} more'
  const templateInput = {
    baz : 'BAR',
    a   : 1,
  }

  const result = interpolate(input, templateInput)
  const expectedResult = 'foo is undefined even 1 more'

  expect(result).toEqual(expectedResult)
})

test('with arbitrary expression', () => {
  const input = '1 + 2 = {{ 1 + 2 }}'
  const templateInput = {}

  const result = interpolate(input, templateInput)

  expect(result).toEqual(input)
})

intersection

It loops through listA and listB and returns the intersection of the two according to R.equals.

💥 There is slight difference between Rambda and Ramda implementation. Ramda.intersection(['a', 'b', 'c'], ['c', 'b']) result is "[ 'c', 'b' ]", but Rambda result is "[ 'b', 'c' ]".

Try this R.intersection example in Rambda REPL

intersperse

It adds a separator between members of list.

Try this R.intersperse example in Rambda REPL

is

It returns true if x is instance of targetPrototype.

Try this R.is example in Rambda REPL

isEmpty

isEmpty<T>(x: T): boolean

It returns true if x is empty.

const result = [
  R.isEmpty(''),
  R.isEmpty({ x : 0 })
]
// => [true, false]

Try this R.isEmpty example in Rambda REPL

R.isEmpty source

import { type } from './type.js'

export function isEmpty(input){
  const inputType = type(input)
  if ([ 'Undefined', 'NaN', 'Number', 'Null' ].includes(inputType))
    return false
  if (!input) return true

  if (type(input.isEmpty) === 'Function') {
	return input.isEmpty();
  } else if (input.isEmpty) {
	return !!input.isEmpty;
  }

  if (inputType === 'Object'){
    return Object.keys(input).length === 0
  }

  if (inputType === 'Array'){
    return input.length === 0
  }

  return false
}

Tests

import { isEmpty } from './isEmpty.js'

test('happy', () => {
  expect(isEmpty(undefined)).toBeFalse()
  expect(isEmpty('')).toBeTrue()
  expect(isEmpty(null)).toBeFalse()
  expect(isEmpty(' ')).toBeFalse()
  expect(isEmpty(new RegExp(''))).toBeFalse()
  expect(isEmpty([])).toBeTrue()
  expect(isEmpty([ [] ])).toBeFalse()
  expect(isEmpty({})).toBeTrue()
  expect(isEmpty({ x : 0 })).toBeFalse()
  expect(isEmpty(0)).toBeFalse()
  expect(isEmpty(NaN)).toBeFalse()
  expect(isEmpty([ '' ])).toBeFalse()
  expect(isEmpty({ isEmpty: false})).toBeFalse()
  expect(isEmpty({ isEmpty: () => false})).toBeFalse()
  expect(isEmpty({ isEmpty: true})).toBeTrue()
  expect(isEmpty({ isEmpty: () => true})).toBeTrue()
})

isNil

isNil(x: any): x is null | undefined

It returns true if x is either null or undefined.

const result = [
  R.isNil(null),
  R.isNil(1),
]
// => [true, false]

Try this R.isNil example in Rambda REPL

R.isNil source

export function isNil(x){
  return x === undefined || x === null
}

Tests

import { isNil } from './isNil.js'

test('happy', () => {
  expect(isNil(null)).toBeTrue()

  expect(isNil(undefined)).toBeTrue()

  expect(isNil([])).toBeFalse()
})

isNotNil

Try this R.isNotNil example in Rambda REPL

isPromise

isPromise(input: any): boolean

isType

isType(targetType: RambdaTypes, input: any): boolean

It returns true if targetType is equal to type of input according to R.type.

R.isType('Async',R.delay(1000))
// => true

Try this R.isType example in Rambda REPL

R.isType source

import { type } from './type.js'

export function isType(xType, x){
  if (arguments.length === 1){
    return xHolder => isType(xType, xHolder)
  }

  return type(x) === xType
}

Tests

import { delay } from './delay.js'
import { isType } from './isType.js'

const list = [ 1, 2, 3 ]

test('array', () => {
  expect(isType('Array', list)).toBeTruthy()
  expect(isType('Array')([])).toBeTruthy()
})

test('promise', () => {
  expect(isType('Promise', Promise.resolve(1))).toBeTruthy()
})

test('async', () => {
  async function fn(){}

  expect(isType('Promise', fn)).toBeTruthy()
})

test('with R.delay', () => {
  expect(isType('Function', delay)).toBeTruthy()
  expect(isType('Promise', delay(100))).toBeTruthy()
})

isValid

isValid({input: object, schema: Schema}: IsValid): boolean

It checks if input is following schema specifications.

If validation fails, it returns false.

Please check the detailed explanation as it is hard to write a short description for this method.

💥 Independently, somebody else came with very similar idea called superstruct

const input = {a: ['foo', 'bar']}
const invalidInput = {a: ['foo', 'bar', 1]}
const schema = {a: [String]}
const result = [
  R.isValid({schema, input}),
  R.isValid({schema, input: invalidInput})
]
// => [true, false]

Try this R.isValid example in Rambda REPL

R.isValid source

import { isArray } from './_internals/isArray.js'
import { all } from './all.js'
import { any } from './any.js'
import { includes } from './includes.js'
import { init } from './init.js'
import { test } from './test.js'
import { toLower } from './toLower.js'
import { type } from './type.js'

export function isPrototype(input){
  const currentPrototype = input.prototype
  const list = [ Number, String, Boolean, Promise ]
  let toReturn = false
  let counter = -1
  while (++counter < list.length && !toReturn){
    if (currentPrototype === list[ counter ].prototype) toReturn = true
  }

  return toReturn
}

export function prototypeToString(input){
  const currentPrototype = input.prototype
  const list = [ Number, String, Boolean, Promise ]
  const translatedList = [ 'Number', 'String', 'Boolean', 'Promise' ]
  let found
  let counter = -1

  while (++counter < list.length){
    if (currentPrototype === list[ counter ].prototype) found = counter
  }

  return translatedList[ found ]
}

const typesWithoutPrototype = [ 'any', 'promise', 'async', 'function' ]

export function fromPrototypeToString(rule){
  if (
    isArray(rule) ||
    rule === undefined ||
    rule === null ||
    rule.prototype === undefined ||
    typesWithoutPrototype.includes(rule)
  ){
    return {
      rule,
      parsed : false,
    }
  }
  if (String.prototype === rule.prototype){
    return {
      rule   : 'string',
      parsed : true,
    }
  }
  if (Boolean.prototype === rule.prototype){
    return {
      rule   : 'boolean',
      parsed : true,
    }
  }
  if (Number.prototype === rule.prototype){
    return {
      rule   : 'number',
      parsed : true,
    }
  }

  return {
    rule   : type(rule.prototype).toLowerCase(),
    parsed : true,
  }
}

function getRuleAndType(schema, requirementRaw){
  const ruleRaw = schema[ requirementRaw ]
  const typeIs = type(ruleRaw)
  const { rule, parsed } = fromPrototypeToString(ruleRaw)

  return {
    rule,
    ruleType : parsed ? 'String' : typeIs,
  }
}

export function isValid({ input, schema }){
  if (input === undefined || schema === undefined) return false

  let flag = true
  const boom = boomFlag => {
    if (!boomFlag){
      flag = false
    }
  }

  for (const requirementRaw in schema){
    if (flag){
      const isOptional = requirementRaw.endsWith('?')
      const requirement = isOptional ? init(requirementRaw) : requirementRaw

      const { rule, ruleType } = getRuleAndType(schema, requirementRaw)
      const inputProp = input[ requirement ]
      const inputPropType = type(input[ requirement ])

      const ok = isOptional && inputProp !== undefined || !isOptional

      if (!ok || rule === 'any' && inputProp != null || rule === inputProp)
        continue

      if (ruleType === 'Object'){
        /**
         * This rule is standalone schema, so we recursevly call `isValid`
         */
        const isValidResult = isValid({
          input  : inputProp,
          schema : rule,
        })
        boom(isValidResult)
      } else if (ruleType === 'String'){
        /**
         * Rule is actual rule such as 'number', so the two types are compared
         */
        boom(toLower(inputPropType) === rule)
      } else if (typeof rule === 'function'){
        /**
         * Rule is function so we pass to it the input
         */
        boom(rule(inputProp))
      } else if (ruleType === 'Array' && inputPropType === 'String'){
        /**
         * Enum case | rule is like a: ['foo', 'bar']
         */
        boom(includes(inputProp, rule))
      } else if (
        ruleType === 'Array' &&
        rule.length === 1 &&
        inputPropType === 'Array'
      ){
        /**
         * 1. array of type | rule is like a: ['number']
         * 2. rule is like a: [{foo: 'string', bar: 'number'}]
         */
        const [ currentRule ] = rule
        const currentRuleType = type(currentRule)

        //Check if rule is invalid
        boom(currentRuleType === 'String' ||
            currentRuleType === 'Object' ||
            isPrototype(currentRule))

        if (currentRuleType === 'Object' && flag){
          /**
           * 2. rule is like a: [{from: 'string'}]
           */
          const isValidResult = all(inputPropInstance =>
            isValid({
              input  : inputPropInstance,
              schema : currentRule,
            }),
          inputProp)
          boom(isValidResult)
        } else if (flag){
          /**
           * 1. array of type
           */

          const actualRule =
            currentRuleType === 'String' ?
              currentRule :
              prototypeToString(currentRule)
          const isInvalidResult = any(inputPropInstance =>
            type(inputPropInstance).toLowerCase() !==
              actualRule.toLowerCase(),
          inputProp)
          boom(!isInvalidResult)
        }
      } else if (ruleType === 'RegExp' && inputPropType === 'String'){
        boom(test(rule, inputProp))
      } else {
        boom(false)
      }
    }
  }

  return flag
}

Tests

import { delay } from './delay.js'
import { isPrototype, isValid } from './isValid.js'

test('is prototype', () => {
  expect(isPrototype(Promise)).toBeTrue()
  expect(isPrototype(Number)).toBeTrue()
  expect(isPrototype(Boolean)).toBeTrue()
  expect(isPrototype(String)).toBeTrue()
  expect(isPrototype(0)).toBeFalse()
})

test('prototype inside array', () => {
  const input = { a : [ 1, 2, 3, 4 ] }
  const schema = { a : [ Number ] }
  expect(isValid({
    input,
    schema,
  })).toBeTruthy()
})

test('with Promise prototype', () => {
  const input = { a : [ delay(1), delay(2) ] }
  const schema = { a : [ Promise ] }
  expect(isValid({
    input,
    schema,
  })).toBeTruthy()
})

test('object prototype as rule - true', () => {
  const input = { a : {} }
  const schema = { a : Object }
  expect(isValid({
    input,
    schema,
  })).toBeTruthy()
})

test('list of functions', () => {
  const input = { a : [ () => {}, delay ] }
  const schema = { a : [ 'function' ] }

  expect(isValid({
    input,
    schema,
  })).toBeTruthy()
})

test('function schema type can be only string', () => {
  const input = { a : [ () => {}, delay ] }
  const schema = { a : [ Function ] }

  expect(isValid({
    input,
    schema,
  })).toBeFalsy()
})

test('object prototype as rule - false', () => {
  const input = { a : null }
  const schema = { a : Object }
  expect(isValid({
    input,
    schema,
  })).toBeFalsy()
})

test('number prototype as rule - true', () => {
  const input = { a : 1 }
  const schema = { a : Number }
  expect(isValid({
    input,
    schema,
  })).toBeTruthy()
})

test('array prototype as rule - true', () => {
  const input = { a : [ 1, 2, 3 ] }
  const schema = { a : Array }
  expect(isValid({
    input,
    schema,
  })).toBeTruthy()
})

test('array prototype as rule - false', () => {
  const input = { a : null }
  const schema = { a : Array }
  expect(isValid({
    input,
    schema,
  })).toBeFalsy()
})

test('string prototype as rule - true', () => {
  const input = { a : 'foo' }
  const schema = { a : String }
  expect(isValid({
    input,
    schema,
  })).toBeTruthy()
})

test('string prototype as rule - false', () => {
  const input = { a : null }
  const schema = { a : String }
  expect(isValid({
    input,
    schema,
  })).toBeFalsy()
})

test('boolean prototype as rule - true', () => {
  const input = { a : true }
  const schema = { a : Boolean }
  expect(isValid({
    input,
    schema,
  })).toBeTruthy()
})

test('boolean prototype as rule - false', () => {
  const input = { a : null }
  const schema = { a : Boolean }
  expect(isValid({
    input,
    schema,
  })).toBeFalsy()
})

test('regex prototype cannot be rule - true', () => {
  const input = { a : /foo/g }
  const schema = { a : new RegExp('foo') }
  expect(isValid({
    input,
    schema,
  })).toBeFalsy()
})

test('undefined as a rule - true', () => {
  const input = { a : undefined }
  const schema = { a : undefined }
  expect(isValid({
    input,
    schema,
  })).toBeTruthy()
})

test('undefined as a rule - false', () => {
  const input = { a : null }
  const schema = { a : undefined }
  expect(isValid({
    input,
    schema,
  })).toBeFalsy()
})

test('null as a rule - true', () => {
  const input = { a : null }
  const schema = { a : null }
  expect(isValid({
    input,
    schema,
  })).toBeTruthy()
})

test('null as a rule - false', () => {
  const input = { a : undefined }
  const schema = { a : null }
  expect(isValid({
    input,
    schema,
  })).toBeFalsy()
})

test('`any` safeguard against `null`', () => {
  const input = { a : null }
  const schema = { a : 'any' }
  expect(isValid({
    input,
    schema,
  })).toBeFalsy()
})

test('`any` safeguard against `undefined`', () => {
  const input = { a : undefined }
  const schema = { a : 'any' }
  expect(isValid({
    input,
    schema,
  })).toBeFalsy()
})

test('type can be `"any"`', () => {
  const input = { a : () => {} }
  const schema = { a : 'any' }
  expect(isValid({
    input,
    schema,
  })).toBeTruthy()
})

test('type can be `"function"`', () => {
  const input = { a : () => {} }
  const schema = { a : 'function' }
  expect(isValid({
    input,
    schema,
  })).toBeTruthy()
})

test('type can be `promise`', () => {
  const input = {
    a : delay(1999),
    b : async () => {},
  }
  const schema = {
    a : 'promise',
    b : 'promise',
  }
  expect(isValid({
    input,
    schema,
  })).toBeTruthy()
})

test('type can be `promise` list', () => {
  const input = { a : [ delay(1999) ] }
  const schema = { a : [ 'promise' ] }
  expect(isValid({
    input,
    schema,
  })).toBeTruthy()
})

test('function as schema - false', () => {
  const input = {
    a : {
      ab : () => true,
      ac : 3,
    },
    c : [ 1, 2 ],
  }
  const schema = {
    'a' : {
      ab : /fo/,
      ac : 'number',
    },
    'b?' : 'string',
    'c'  : [ 'number' ],
  }
  expect(isValid({
    input,
    schema,
  })).toBeFalsy()
})

test('regex ok', () => {
  const input = {
    a : {
      ab : 'foo',
      ac : 3,
    },
    c : [ 1, 2 ],
  }
  const schema = {
    'a' : {
      ab : /fo/,
      ac : 'number',
    },
    'b?' : 'string',
    'c'  : [ 'number' ],
  }
  expect(isValid({
    input,
    schema,
  })).toBeTruthy()
})

test('regex !ok', () => {
  const input = {
    a : {
      ab : 'foo',
      ac : 3,
    },
    c : [ 1, 2 ],
  }
  const schema = {
    'a' : {
      ab : /ba/,
      ac : 'number',
    },
    'b?' : 'string',
    'c'  : [ 'number' ],
  }
  expect(isValid({
    input,
    schema,
  })).toBeFalsy()
})

test('optional props is missing', () => {
  const input = {
    a : {
      ab : 'foo',
      ac : 3,
    },
    c : [ 1, 2 ],
  }
  const schema = {
    'a' : {
      ab : 'string',
      ac : 'number',
    },
    'b?' : 'string',
    'c'  : [ 'number' ],
  }
  expect(isValid({
    input,
    schema,
  })).toBeTruthy()
})

test('optional props is wrong type', () => {
  const input = {
    a : {
      ab : 'foo',
      ac : 3,
    },
    b : [],
    c : [ 1, 2 ],
  }
  const schema = {
    'a' : {
      ab : 'string',
      ac : 'number',
    },
    'b?' : 'string',
    'c'  : [ 'number' ],
  }
  expect(isValid({
    input,
    schema,
  })).toBeFalsy()
})

test('optional props - nested', () => {
  const input = {
    a : {
      ab : 'foo',
      ac : 3,
    },
    b : [],
    c : [ 1, 2 ],
  }
  const schema = {
    a : {
      'ab'  : 'string',
      'ac?' : 'number',
    },
    b : 'array',
    c : [ 'number' ],
  }
  expect(isValid({
    input,
    schema,
  })).toBeTruthy()
})

test('optional props is missing - nested', () => {
  const input = {
    a : { ab : 'foo' },
    b : [],
    c : [ 1, 2 ],
  }
  const schema = {
    a : {
      'ab'  : 'string',
      'ac?' : 'number',
    },
    b : 'array',
    c : [ 'number' ],
  }
  expect(isValid({
    input,
    schema,
  })).toBeTruthy()
})

test('optional props is wrong type - nested', () => {
  const input = {
    a : {
      ab : 'foo',
      ac : 'bar',
    },
    b : [],
    c : [ 1, 2 ],
  }
  const schema = {
    a : {
      'ab'  : 'string',
      'ac?' : 'number',
    },
    b : 'array',
    c : [ 'number' ],
  }
  expect(isValid({
    input,
    schema,
  })).toBeFalsy()
})

test('nested schema', () => {
  const input = {
    a : {
      b : 'str',
      c : 3,
      d : 'str',
    },
    b : 'foo',
  }
  const schema = {
    a : {
      b : 'string',
      c : 'number',
      d : 'string',
    },
    b : 'string',
  }

  expect(isValid({
    input,
    schema,
  })).toBeTruthy()

  const invalidInputFirst = {
    a : {
      b : 'str',
      c : 3,
      d : 'str',
    },
    b : 5,
  }

  expect(isValid({
    input : invalidInputFirst,
    schema,
  })).toBeFalsy()

  const invalidInputSecond = {
    a : {
      b : 'str',
      c : 'str',
      d : 'str',
    },
    b : 5,
  }

  expect(isValid({
    input : invalidInputSecond,
    schema,
  })).toBeFalsy()

  const invalidInputThird = {
    a : { b : 'str' },
    b : 5,
  }

  expect(isValid({
    input : invalidInputThird,
    schema,
  })).toBeFalsy()
})

test('array of type', () => {
  const input = {
    a : [ 1, 2 ],
    b : 'foo',
  }
  const schema = {
    a : [ 'number' ],
    b : 'string',
  }

  expect(isValid({
    input,
    schema,
  })).toBeTruthy()

  const invalidInput = {
    a : [ 1, '1' ],
    b : 'foo',
  }

  expect(isValid({
    input : invalidInput,
    schema,
  })).toBeFalsy()
})

test('function as rule', () => {
  const input = {
    a : [ 1, 2, 3, 4 ],
    b : 'foo',
  }
  const invalidInput = {
    a : [ 4 ],
    b : 'foo',
  }

  const schema = {
    a : x => x.length > 2,
    b : 'string',
  }

  expect(isValid({
    input,
    schema,
  })).toBeTruthy()

  expect(isValid({
    input : invalidInput,
    schema,
  })).toBeFalsy()
})

test('input prop is undefined', () => {
  const input = { b : 3 }
  const schema = { a : 'number' }

  expect(isValid({
    input,
    schema,
  })).toBeFalsy()
})

test('enum', () => {
  const input = { a : 'foo' }
  const invalidInput = { a : '' }

  const schema = { a : [ 'foo', 'bar', 'baz' ] }

  expect(isValid({
    input,
    schema,
  })).toBeTruthy()

  expect(isValid({
    input : invalidInput,
    schema,
  })).toBeFalsy()
})

test('readme example', () => {
  const basicSchema = { a : [ 'string' ] }
  const schema = {
    b : [ basicSchema ],
    c : {
      d : { e : 'boolean' },
      f : 'array',
    },
    g : [ 'foo', 'bar', 'baz' ],
  }
  const input = {
    b : [ { a : [ 'led', 'zeppelin' ] } ],
    c : {
      d : { e : true },
      f : [ 'any', 1, null, 'value' ],
    },
    g : 'foo',
  }

  expect(isValid({
    input,
    schema,
  })).toBeTruthy()
})

test('should allow additional properties', () => {
  const input = {
    title : 'You shook me',
    year  : 1969,
  }

  expect(isValid({
    input,
    schema : { title : 'string' },
  })).toBeTruthy()
})

test('accepts values as schemas', () => {
  const input = {
    title : 'You shook me',
    genre : 'Blues',
    year  : 1969,
  }
  const schema = {
    title : 'You shook me',
    year  : 1969,
  }
  expect(isValid({
    input,
    schema,
  })).toBeTruthy()
})

test('compatible schemas with nested object', () => {
  const input = {
    foo : 'bar',
    baz : { a : { b : 'c' } },
  }
  const invalidInputFirst = {
    foo : 'bar',
    baz : { a : { b : 1 } },
  }
  const invalidInputSecond = {
    foo : 'bar',
    baz : { a : { b : [] } },
  }
  const invalidInputThird = {
    foo : 'bar',
    baz : { a : { b : null } },
  }
  const schema = {
    foo : 'string',
    baz : { a : { b : 'string' } },
  }

  expect(isValid({
    input,
    schema,
  })).toBeTruthy()

  expect(isValid({
    input : invalidInputFirst,
    schema,
  })).toBeFalsy()
  expect(isValid({
    input : invalidInputSecond,
    schema,
  })).toBeFalsy()
  expect(isValid({
    input : invalidInputThird,
    schema,
  })).toBeFalsy()
})

test('should return true when schema is empty object', () => {
  expect(isValid({
    input  : { a : 1 },
    schema : {},
  })).toBeTruthy()
})

test('when schema is undefined', () => {
  expect(isValid({
    input  : { a : 1 },
    schema : undefined,
  })).toBeFalsy()
})

test('should return false with invalid schema rule', () => {
  const input = {
    foo : 'bar',
    a   : {},
  }
  const inputSecond = { foo : 'bar' }

  const schema = {
    foo : 'string',
    baz : { a : {} },
  }

  expect(isValid({
    input,
    schema,
  })).toBeFalsy()

  expect(isValid({
    input : inputSecond,
    schema,
  })).toBeFalsy()
})

test('array of schemas', () => {
  const input = {
    b : [
      {
        a : 'led',
        b : 1,
      },
      {
        a : 'dancing',
        b : 1,
      },
    ],
  }
  const basicSchema = {
    a : String,
    b : Number,
  }
  const schema = { b : [ basicSchema ] }
  const result = isValid({
    input,
    schema,
  })

  expect(result).toBeTruthy()
})

isValidAsync

isValidAsync(x: IsValidAsync): Promise<boolean>

Asynchronous version of R.isValid

const input = {a: 1, b: 2}
const invalidInput = {a: 1, b: 'foo'}
const schema = {a: Number, b: async x => {
  await R.delay(100)
  return typeof x === 'number'
}}

const result = await Promise.all([
  R.isValidAsync({schema, input}),
  R.isValidAsync({schema, input: invalidInput})
])
// => [true, false]

Try this R.isValidAsync example in Rambda REPL

R.isValidAsync source

import { forEach } from './forEach.js'
import { isPromise } from './isPromise.js'
import { isValid } from './isValid.js'

export async function isValidAsync({ schema, input }){
  const asyncSchema = {}
  const simpleSchema = {}
  forEach((rule, prop) => {
    if (isPromise(rule)){
      asyncSchema[ prop ] = rule
    } else {
      simpleSchema[ prop ] = rule
    }
  }, schema)

  if (Object.keys(asyncSchema).length === 0)
    return isValid({
      input,
      schema,
    })

  if (
    !isValid({
      input,
      schema : simpleSchema,
    })
  )
    return false

  let toReturn = true

  for (const singleRuleProp in asyncSchema){
    if (toReturn){
      const validated = await asyncSchema[ singleRuleProp ](input[ singleRuleProp ])
      if (!validated) toReturn = false
    }
  }

  return toReturn
}

Tests

import { result } from 'lodash'

import { delay } from './delay.js'
import { isValidAsync } from './isValidAsync.js'

const simplePredicate = async x => {
  await delay(100)

  return x > 5
}

test('happy', async () => {
  const input = {
    a          : 1,
    b          : 7,
    c          : 9,
    additional : 'foo',
  }
  const invalidInput = {
    a : 1,
    b : 2,
    c : 9,
  }
  const schema = {
    a : Number,
    b : simplePredicate,
    c : simplePredicate,
  }
  const invalidSchema = {
    a : Boolean,
    b : simplePredicate,
    c : simplePredicate,
  }
  const result = await isValidAsync({
    input,
    schema,
  })
  const invalidResult = await isValidAsync({
    input,
    schema : invalidSchema,
  })
  const withInvalidInput = await isValidAsync({
    input : invalidInput,
    schema,
  })
  expect(result).toBeTruthy()
  expect(invalidResult).toBeFalsy()
  expect(withInvalidInput).toBeFalsy()
})

test('without async rules', async () => {
  const input = {
    a : 1,
    b : 7,
  }
  const schema = {
    a : Number,
    b : x => x > 2,
  }
  const invalidSchema = {
    a : Number,
    b : Boolean,
  }
  const result = await isValidAsync({
    input,
    schema,
  })
  const invalidResult = await isValidAsync({
    input,
    schema : invalidSchema,
  })

  expect(result).toBeTruthy()
  expect(invalidResult).toBeFalsy()
})

test('readme example', async () => {
  const input = {
    a : 1,
    b : 2,
  }
  const invalidInput = {
    a : 1,
    b : 'foo',
  }
  const schema = {
    a : Number,
    b : async x => {
      await delay(100)

      return typeof x === 'number'
    },
  }
  const result = await Promise.all([
    isValidAsync({
      schema,
      input,
    }),
    isValidAsync({
      schema,
      input : invalidInput,
    }),
  ])
  expect(result).toEqual([ true, false ])
})

join

join<T>(glue: string, list: T[]): string

It returns a string of all list instances joined with a glue.

R.join('-', [1, 2, 3])  // => '1-2-3'

Try this R.join example in Rambda REPL

R.join source

export function join(glue, list){
  if (arguments.length === 1) return _list => join(glue, _list)

  return list.join(glue)
}

Tests

import { join } from './join.js'

test('curry', () => {
  expect(join('|')([ 'foo', 'bar', 'baz' ])).toBe('foo|bar|baz')

  expect(join('|', [ 1, 2, 3 ])).toBe('1|2|3')

  const spacer = join(' ')

  expect(spacer([ 'a', 2, 3.4 ])).toBe('a 2 3.4')
})

juxt

juxt<A extends any[], R1>(fns: [(...a: A) => R1]): (...a: A) => [R1]

It applies list of function to a list of inputs.

const getRange = juxt([ Math.min, Math.max, Math.min ])
const result = getRange(
  3, 4, 9, -3
)
// => [-3, 9, -3]

Try this R.juxt example in Rambda REPL

R.juxt source

export function juxt(listOfFunctions){
  return (...args) => listOfFunctions.map(fn => fn(...args))
}

Tests

import { juxt } from './juxt.js'

test('happy', () => {
  const fn = juxt([ Math.min, Math.max, Math.min ])
  const result = fn(
    3, 4, 9, -3
  )
  expect(result).toEqual([ -3, 9, -3 ])
})

keys

keys<T extends object>(x: T): (keyof T & string)[]

It applies Object.keys over x and returns its keys.

R.keys({a:1, b:2})  // => ['a', 'b']

Try this R.keys example in Rambda REPL

R.keys source

export function keys(x){
  return Object.keys(x)
}

Tests

import { keys } from './keys.js'

test('happy', () => {
  expect(keys({ a : 1 })).toEqual([ 'a' ])
})

last

last(str: ''): undefined

It returns the last element of input, as the input can be either a string or an array.

const result = [
  R.last([1, 2, 3]),
  R.last('foo'),
]
// => [3, 'o']

Try this R.last example in Rambda REPL

R.last source

export function last(listOrString){
  if (typeof listOrString === 'string'){
    return listOrString[ listOrString.length - 1 ] || ''
  }

  return listOrString[ listOrString.length - 1 ]
}

Tests

import { last } from './last.js'

test('with list', () => {
  expect(last([ 1, 2, 3 ])).toBe(3)
  expect(last([])).toBeUndefined()
})

test('with string', () => {
  expect(last('abc')).toBe('c')
  expect(last('')).toBe('')
})

lastIndexOf

lastIndexOf<T>(target: T, list: T[]): number

It returns the last index of target in list array.

R.equals is used to determine equality between target and members of list.

If there is no such index, then -1 is returned.

const list = [1, 2, 3, 1, 2, 3]
const result = [
  R.lastIndexOf(2, list),
  R.lastIndexOf(4, list),
]
// => [4, -1]

Try this R.lastIndexOf example in Rambda REPL

R.lastIndexOf source

import { _lastIndexOf } from './equals.js'

export function lastIndexOf(valueToFind, list){
  if (arguments.length === 1){
    return _list => _lastIndexOf(valueToFind, _list)
  }

  return _lastIndexOf(valueToFind, list)
}

Tests

import { lastIndexOf as lastIndexOfRamda } from 'ramda'

import { compareCombinations } from './_internals/testUtils.js'
import { possibleIterables, possibleTargets } from './indexOf.spec.js'
import { lastIndexOf } from './lastIndexOf.js'

test('with NaN', () => {
  expect(lastIndexOf(NaN, [ NaN ])).toBe(0)
})

test('will throw with bad input', () => {
  expect(lastIndexOfRamda([], true)).toBe(-1)
  expect(() => indexOf([], true)).toThrowErrorMatchingInlineSnapshot('"indexOf is not defined"')
})

test('without list of objects - no R.equals', () => {
  expect(lastIndexOf(3, [ 1, 2, 3, 4 ])).toBe(2)
  expect(lastIndexOf(10)([ 1, 2, 3, 4 ])).toBe(-1)
})

test('list of objects uses R.equals', () => {
  const listOfObjects = [ { a : 1 }, { b : 2 }, { c : 3 } ]
  expect(lastIndexOf({ c : 4 }, listOfObjects)).toBe(-1)
  expect(lastIndexOf({ c : 3 }, listOfObjects)).toBe(2)
})

test('list of arrays uses R.equals', () => {
  const listOfLists = [ [ 1 ], [ 2, 3 ], [ 2, 3, 4 ], [ 2, 3 ], [ 1 ], [] ]
  expect(lastIndexOf([], listOfLists)).toBe(5)
  expect(lastIndexOf([ 1 ], listOfLists)).toBe(4)
  expect(lastIndexOf([ 2, 3, 4 ], listOfLists)).toBe(2)
  expect(lastIndexOf([ 2, 3, 5 ], listOfLists)).toBe(-1)
})

test('with string as iterable', () => {
  expect(() => lastIndexOf('a', 'abc')).toThrowErrorMatchingInlineSnapshot('"Cannot read property \'indexOf\' of abc"')
  expect(lastIndexOfRamda('a', 'abc')).toBe(0)
})

describe('brute force', () => {
  compareCombinations({
    fn          : lastIndexOf,
    fnRamda     : lastIndexOfRamda,
    firstInput  : possibleTargets,
    secondInput : possibleIterables,
    callback    : errorsCounters => {
      expect(errorsCounters).toMatchInlineSnapshot(`
        {
          "ERRORS_MESSAGE_MISMATCH": 0,
          "ERRORS_TYPE_MISMATCH": 34,
          "RESULTS_MISMATCH": 0,
          "SHOULD_NOT_THROW": 51,
          "SHOULD_THROW": 0,
          "TOTAL_TESTS": 170,
        }
      `)
    },
  })
})

length

length<T>(input: T[]): number

It returns the length property of list or string input.

const result = [
  R.length([1, 2, 3, 4]),
  R.length('foo'),
]
// => [4, 3]

Try this R.length example in Rambda REPL

R.length source

import { isArray } from './_internals/isArray.js'

export function length(x){
  if (isArray(x)) return x.length
  if (typeof x === 'string') return x.length

  return NaN
}

Tests

import { length as lengthRamda } from 'ramda'

import { length } from './length.js'

test('happy', () => {
  expect(length('foo')).toBe(3)
  expect(length([ 1, 2, 3 ])).toBe(3)
  expect(length([])).toBe(0)
})

test('with empty string', () => {
  expect(length('')).toBe(0)
})

test('with bad input returns NaN', () => {
  expect(length(0)).toBeNaN()
  expect(length({})).toBeNaN()
  expect(length(null)).toBeNaN()
  expect(length(undefined)).toBeNaN()
})

test('with length as property', () => {
  const input1 = { length : '123' }
  const input2 = { length : null }
  const input3 = { length : '' }

  expect(length(input1)).toBeNaN()
  expect(lengthRamda(input1)).toBeNaN()
  expect(length(input2)).toBeNaN()
  expect(lengthRamda(input2)).toBeNaN()
  expect(length(input3)).toBeNaN()
  expect(lengthRamda(input3)).toBeNaN()
})

lens

lens<S, A>(getter: (s: S) => A, setter: (a: A, s: S) => S): Lens<S, A>

It returns a lens for the given getter and setter functions.

The getter gets the value of the focus; the setter sets the value of the focus.

The setter should not mutate the data structure.

const xLens = R.lens(R.prop('x'), R.assoc('x'));

R.view(xLens, {x: 1, y: 2}) // => 1
R.set(xLens, 4, {x: 1, y: 2}) // => {x: 4, y: 2}
R.over(xLens, R.negate, {x: 1, y: 2}) // => {x: -1, y: 2}

Try this R.lens example in Rambda REPL

R.lens source

export function lens(getter, setter){
  return function (functor){
    return function (target){
      return functor(getter(target)).map(focus => setter(focus, target))
    }
  }
}

lensEq

lensEq(lens: Function, value: any, data: any): boolean

It returns true if data structure focused by the given lens equals to the target value.

R.equals is used to determine equality.

💥 Idea for this method comes from ramda-adjunct library

const list = [ 1, 2, 3 ]
const lens = R.lensIndex(0)
const result = R.lensEq(
  lens, 1, list
)
// => true

Try this R.lensEq example in Rambda REPL

R.lensEq source

import { curry } from './curry.js'
import { equals } from './equals.js'
import { view } from './view.js'

function lensEqFn(
  lens, target, input
){
  return equals(view(lens, input), target)
}

export const lensEq = curry(lensEqFn)

Tests

import { lensEq } from './lensEq.js'
import { lensIndex } from './lensIndex.js'
import { lensPath } from './lensPath.js'

test('with list', () => {
  const list = [ 1, 2, 3 ]
  const lens = lensIndex(0)
  expect(lensEq(
    lens, 1, list
  )).toBeTrue()
  expect(lensEq(lens, 2)(list)).toBeFalse()
})

test('with R.lensPath', () => {
  const input = { a : { b : { c : 1 } } }
  const target = { c : 1 }
  const lens = lensPath('a.b')

  expect(lensEq(lens)(target)(input)).toBeTrue()
  expect(lensEq(
    lens, target, { c : 2 }
  )).toBeFalse()
})

lensIndex

lensIndex<A>(n: number): Lens<A[], A>

It returns a lens that focuses on specified index.

const list = ['a', 'b', 'c']
const headLens = R.lensIndex(0)

R.view(headLens, list) // => 'a'
R.set(headLens, 'x', list) // => ['x', 'b', 'c']
R.over(headLens, R.toUpper, list) // => ['A', 'b', 'c']

Try this R.lensIndex example in Rambda REPL

R.lensIndex source

import { lens } from './lens.js'
import { nth } from './nth.js'
import { update } from './update.js'

export function lensIndex(index){
  return lens(nth(index), update(index))
}

Tests

import { compose } from './compose.js'
import { keys } from './keys.js'
import { lensIndex } from './lensIndex.js'
import { over } from './over.js'
import { set } from './set.js'
import { view } from './view.js'

const testList = [ { a : 1 }, { b : 2 }, { c : 3 } ]

test('focuses list element at the specified index', () => {
  expect(view(lensIndex(0), testList)).toEqual({ a : 1 })
})

test('returns undefined if the specified index does not exist', () => {
  expect(view(lensIndex(10), testList)).toBeUndefined()
})

test('sets the list value at the specified index', () => {
  expect(set(
    lensIndex(0), 0, testList
  )).toEqual([ 0, { b : 2 }, { c : 3 } ])
})

test('applies function to the value at the specified list index', () => {
  expect(over(
    lensIndex(2), keys, testList
  )).toEqual([ { a : 1 }, { b : 2 }, [ 'c' ] ])
})

test('can be composed', () => {
  const nestedList = [ 0, [ 10, 11, 12 ], 1, 2 ]
  const composedLens = compose(lensIndex(1), lensIndex(0))

  expect(view(composedLens, nestedList)).toBe(10)
})

test('set s (get s) === s', () => {
  expect(set(
    lensIndex(0), view(lensIndex(0), testList), testList
  )).toEqual(testList)
})

test('get (set s v) === v', () => {
  expect(view(lensIndex(0), set(
    lensIndex(0), 0, testList
  ))).toBe(0)
})

test('get (set(set s v1) v2) === v2', () => {
  expect(view(lensIndex(0),
    set(
      lensIndex(0), 11, set(
        lensIndex(0), 10, testList
      )
    ))).toBe(11)
})

lensPath

It returns a lens that focuses on specified path.

Try this R.lensPath example in Rambda REPL

lensProp

lensProp<S, K extends keyof S = keyof S>(prop: K): Lens<S, S[K]>

It returns a lens that focuses on specified property prop.

const xLens = R.lensProp('x');
const input = {x: 1, y: 2}

R.view(xLens, input) // => 1

R.set(xLens, 4, input) 
// => {x: 4, y: 2}

R.over(xLens, R.negate, input) 
// => {x: -1, y: 2}

Try this R.lensProp example in Rambda REPL

R.lensProp source

import { assoc } from './assoc.js'
import { lens } from './lens.js'
import { prop } from './prop.js'

export function lensProp(key){
  return lens(prop(key), assoc(key))
}

Tests

import { compose } from './compose.js'
import { identity } from './identity.js'
import { inc } from './inc.js'
import { lensProp } from './lensProp.js'
import { over } from './over.js'
import { set } from './set.js'
import { view } from './view.js'

const testObj = {
  a : 1,
  b : 2,
  c : 3,
}

test('focuses object the specified object property', () => {
  expect(view(lensProp('a'), testObj)).toBe(1)
})

test('returns undefined if the specified property does not exist', () => {
  expect(view(lensProp('X'), testObj)).toBeUndefined()
})

test('sets the value of the object property specified', () => {
  expect(set(
    lensProp('a'), 0, testObj
  )).toEqual({
    a : 0,
    b : 2,
    c : 3,
  })
})

test('adds the property to the object if it doesn\'t exist', () => {
  expect(set(
    lensProp('d'), 4, testObj
  )).toEqual({
    a : 1,
    b : 2,
    c : 3,
    d : 4,
  })
})

test('applies function to the value of the specified object property', () => {
  expect(over(
    lensProp('a'), inc, testObj
  )).toEqual({
    a : 2,
    b : 2,
    c : 3,
  })
})

test('applies function to undefined and adds the property if it doesn\'t exist', () => {
  expect(over(
    lensProp('X'), identity, testObj
  )).toEqual({
    a : 1,
    b : 2,
    c : 3,
    X : undefined,
  })
})

test('can be composed', () => {
  const nestedObj = {
    a : { b : 1 },
    c : 2,
  }
  const composedLens = compose(lensProp('a'), lensProp('b'))

  expect(view(composedLens, nestedObj)).toBe(1)
})

test('set s (get s) === s', () => {
  expect(set(
    lensProp('a'), view(lensProp('a'), testObj), testObj
  )).toEqual(testObj)
})

test('get (set s v) === v', () => {
  expect(view(lensProp('a'), set(
    lensProp('a'), 0, testObj
  ))).toBe(0)
})

test('get (set(set s v1) v2) === v2', () => {
  expect(view(lensProp('a'),
    set(
      lensProp('a'), 11, set(
        lensProp('a'), 10, testObj
      )
    ))).toBe(11)
})

lensSatisfies

lensSatisfies<T, U>(predicate: (x: T) => boolean, lens: Lens, input: U): boolean

It returns true if data structure focused by the given lens satisfies the predicate.

💥 Idea for this method comes from ramda-adjunct library

const fn = R.lensSatisfies(x => x > 5, R.lensIndex(0))
const result = [
  fn([10, 20, 30]),
  fn([1, 2, 3]),
]
// => [true, false]

Try this R.lensSatisfies example in Rambda REPL

R.lensSatisfies source

import { curry } from './curry.js'
import { view } from './view.j