Utils

A collection of utils implemented in TypeScript.

test coverage report

Getting started

npm install acd-utils

Then you can import these:

• result
• maybe

Result

import { err, ok, result, Result } from 'acd-utils'

err

Returns an Err

example

type Error = {
  code: number
}

const error: Error = {
  code: 400,
}

const err: Err = err(error)

ok

Returns an Ok

example

type Data = {
  values: number[]
}

const data: Data = {
  values: [1, 2],
}

const success: Ok = ok(data)

result

Wraps a value of two possible types (Ok | Err) and returns a Result object allowing you to unfold the value to handle both cases.

An instance of Result<E, S> is either an instance of Err or Ok. The first type is used for failure (E), the second for success (S).

Sort of like a really really lightweight unlawful Result monad.

Methods available on the Result object are:

• fold, takes two functions
  • a first function that will get executed if the value is an Err
  • a second function, that will get executed if the value is an Ok

example

import { err, ok, Result, result } from 'acd-utils'

type Item = {
  id: number
  label: string
}

type Error = {
  code: number
}

async function httpGet<Res, Err>(url: string): Promise<Result<Err, Res>> {
  const { error, data } = await fetch(url).then(i => i.json())
  
  return result(error ? err(error) : ok(data as Res))
}

const data = await httpGet<Item, Error>('someUrl')

data.fold(
  e => `the error code is ${e.code}`,
  item => `label is ${item.label}`,
)

Maybe

import { maybe, maybeAll } from 'acd-utils'

maybe

Wraps a potentially nullable value and returns a Box object, allowing you to manipulate the value safely as if it was defined.

Sort of like a really lightweight unlawful Maybe monad.

Methods available on the Box object are:

• map, takes your value as an argument, allowing you to update it safely
• filter, takes your value as an argument, allowing you to return a predicate
• flatMap, if value is defined, calls the function you give on the item in the Box and returns its result
• fold, takes two functions
  • a first function that will get executed if the value is undefined or null, allowing you to return a fallback value.
  • a second function that will get called with the value if defined. The result of this function will be then returned.
• getOrElse, expects a fallback value in case of the initial value was undefined or null
• get, returns your value

map

example

const word: string | undefined = undefined
const result = maybe(word)
  .map(w => w.toUpperCase())
  .map(w => w + '!')
  .get()
// result === undefined

const word2: string | undefined = 'hello'
const result2 = maybe(word2)
  .map(w => w.toUpperCase())
  .map(w => w + '!')
  .get()
// result2 === 'HELLO!'

filter

example

const word: string | undefined = undefined
const result = maybe(word)
  .filter(w => w.length > 2)
  .map(w => w + '!')
  .get()
// result === undefined

const word2: string | undefined = 'ok'
const result2 = maybe(word2)
  .filter(w => w.length > 2)
  .map(w => w + '!')
  .get()
// result2 === undefined

const word3: string | undefined = 'hello'
const result3 = maybe(word3)
  .filter(w => w.length > 2)
  .map(w => w + '!')
  .get()
// result3 === 'hello!'

flatMap

example

type Obj = {
  label?: string
}

const obj: Obj | undefined = {
  label: 'some label'
}

const result = maybe(obj)
  .flatMap(obj => maybe(obj.label).map(label => label.toUpperCase()))
  .get()
// result === 'SOME LABEL'

const obj2: Obj | undefined = undefined

const result2 = maybe(obj2)
  .flatMap(obj => maybe(obj.label).map(label => label.toUpperCase()))
  .get()
// result2 === undefined

fold

example

type Obj = {
  label: string
}

const obj: Obj | undefined = {
  label: 'some label'
}

const result = maybe(obj)
  .fold(
    () => 'oops',
    ({ label }) => label.toUpperCase()
  )
// result === 'SOME LABEL

const obj2: Obj | undefined = undefined

const result2 = maybe(obj2)
  .fold(
    () => 'oops',
    ({ label }) => label.toUpperCase()
  )
// result2 === 'oops'

getOrElse

example

const word: string | undefined = undefined
const result = maybe(word)
  .map(w => w.toUpperCase())
  .map(w => w + '!')
  .getOrElse('fallback')
// result === 'fallback'

const word2: string | undefined = 'hello'
const result2 = maybe(word2)
  .map(w => w.toUpperCase())
  .map(w => w + '!')
  .getOrElse('fallback')
// result2 === 'HELLO!'

get

example

const word: string | undefined = undefined
const result = maybe(word)
  .map(w => w.toUpperCase())
  .map(w => w + '!')
  .get()
// result === undefined

const word2: string | undefined = 'hello'
const result2 = maybe(word2)
  .map(w => w.toUpperCase())
  .map(w => w + '!')
  .get()
// result2 === 'HELLO!'

maybeAll

Wraps a tuple (up to 5 elements) containing potentially nullable values and returns a Box object (containing your tuple), allowing you to manipulate the values safely, as if they were all defined.

For the map, filter methods, or the second function of the fold method to be executed, all values inside the tuple must be defined.

Sort of like a really lightweight unlawful Maybe monad.

Methods available on the Box object are:

• map, takes your value as an argument, allowing you to update it safely
• filter, takes your value as an argument, allowing you to return a predicate
• fold, takes two functions
  • a first function that will get executed if the value is undefined or null, allowing you to return a fallback value.
  • a second function that will get called with the value if defined. The result of this function will be then returned.
• getOrElse, expects a fallback value in case of the initial value was undefined or null
• get, returns your value

example

const word: string | undefined = undefined
const num: number | undefined = 36
const result = maybeAll([word, num])
  .filter(([w]) => w.length > 4)
  .map(([w, n]) => `${String(n)} ${w}`)
  .getOrElse('wu')
// result === 'wu'

const word2: string | undefined = 'chambers'
const num2: number | undefined = 36
const result2= maybeAll([word2, num2])
  .filter(([w]) => w.length > 4)
  .map(([w, n]) => `${String(n)} ${w}`)
  .getOrElse('wu')
// result2 === '36 chambers'

This project was inspired by:

• fp-ts
• space-lift

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