Functional composition library
!npm (scoped)
!CircleCI
!David (path)
!Codecov
!npm bundle size (scoped)
!GitHub
1. Introduction
2. Installation
3. API reference
- chain
- chainRight
- compose
- curry
- pipe
- pipe.now
- rail
- rail.async
- railRight
- railRight.async
- tap
4. License
The library contains a collection of higher-order functions for composing your applications with reusable functions.
All chain-like functions are manually chunked (segmented). It is a deliberate decision (to not use automatic currying) to allow a function to accept a variadic number of arguments in a segment, which leads in my opinion to a nicer to use API (and is faster as a bonus).
The library has built-in type definitions, which provide an excellent IDE support.
Via NPM:
``sh`
npm i @arrows/composition
Via Yarn:
`sh`
yarn add @arrows/composition
All modules can be imported independently (to reduce bundle size), here are some import methods (you can use either CommonJS or ES modules):
`js`
import composition from '@arrows/composition'
`js`
import { pipe } from '@arrows/composition'
`js`
import pipe from '@arrows/composition/pipe'
Allows you to build your own, chain-like functions
Executes provided functions from left to right, passing the result from one function to the other. Accepts a wrapping function which can execute additional instructions before executing each passed function.
#### Parameters
Arguments listed below have to be passed separately, as segments.
- wrappingFn - two-argument function thats is responsible for executing each function in a chain.
- ...fns - an arbitrary number of one-argument functions to be executed in a chain
- initialArg - initial argument, passed to the first function in a chain (through a wrapping function)
Arguments of a wrapping function:
- fn - function in a chain
- input - current value
- isLast - boolean flag indicating if a function is a last one in a chain
#### Returns
- Returns a final value.
#### Interface
`
(wrapping_function) => (fn, fn?, ..., fn?) => (initial_value) => result
#### Examples
`javascript
const { chain } = require('@arrows/composition')
// Create custom wrapping function:
const wrappingFn = (fn, input) => {
console.log(input)
return fn(input)
}
// Create reusable chain-like function:
const pipeWithLog = chain(wrappingFn)
// Create concrete function
const calculate = pipeWithLog((x) => x + 1, (x) => x * 2)
console.log(calculate(0))
// -> 0
// -> 1
// -> 2 (final result)
`
---
Works like chain, but executes functions from right to left.
#### Parameters
Arguments listed below have to be passed separately, as segments.
- wrappingFn - two-argument function thats is responsible for executing each function in a chain.
- ...fns - an arbitrary number of one-argument functions to be executed in a chain
- initialArg - initial argument, passed to the first function in a chain (through a wrapping function)
Arguments of a wrapping function:
- fn - function in a chain
- input - current value
- isLast - boolean flag indicating if a function is a last one in a chain
#### Returns
- Returns a final value.
#### Interface
`
(wrapping_function) => (fn, fn?, ..., fn?) => (initial_value) => result
#### Example
`javascript
const { chainRight } = require('@arrows/composition')
// Create custom wrapping function:
const wrappingFn = (fn, input) => {
console.log(input)
return fn(input)
}
// Create reusable chain-like function:
const composeWithLog = chainRight(wrappingFn)
// Create concrete function
const calculateRight = composeWithLog((x) => x + 1, (x) => x * 2)
console.log(calculateRight(0))
// -> 0
// -> 0
// -> 1 (final result)
`
---
Chains provided functions from right to left.
#### Parameters
Arguments listed below have to be passed separately, as segments.
- ...fns - an arbitrary number of one-argument functions to be executed in a chain
- initialArg - initial argument, passed to the first function in a chain
#### Returns
- Returns a final value.
#### Interface
`
(fn, fn?, ..., fn?) => (initial_value) => result
#### Example
`javascript
const { compose } = require('@arrows/composition')
const addPrefixes = compose(
(text) => prefix1-${text},prefix2-${text}
(text) => ,
)
addPrefixes('arrows') // -> "prefix1-prefix2-arrows"
`
---
Wraps function as an automatically curried one.
#### Parameters
- fn - an arbitrary function
#### Returns
- Returns a curried version of the function.
#### Interface
`
(fn) => curried_fn
#### Example
`javascript
const { curry } = require('@arrows/composition')
const rawAdd = (a, b) => a + b
const add = curry(rawAdd)
add(1, 2) // -> 3
add(1)(2) // -> 3
`
---
Chains provided functions from left to right.
#### Parameters
Arguments listed below have to be passed separately, as segments.
- ...fns - an arbitrary number of one-argument functions to be executed in a chain
- initialArg - initial argument, passed to the first function in a chain
#### Returns
- Returns a final value.
#### Interface
`
(fn, fn?, ..., fn?) => (initial_value) => result
#### Example
`javascript
const { pipe } = require('@arrows/composition')
const addSuffixes = pipe(
(text) => ${text}-suffix1,${text}-suffix2
(text) => ,
)
addSuffixes('arrows') // -> "arrows-suffix1-suffix2"
`
---
Chains provided functions from left to right, takes an initial value as a first argument.
Provides an alternative API with better type inference for immediately evaluated calculations.
#### Parameters
- initialArg - initial argument, passed to the first function in a chain...fns
- - an arbitrary number of one-argument functions to be executed in a chain
#### Returns
- Returns a final value.
#### Interface
`
(initial_value, fn, fn?, ..., fn?) => result
#### Example
`javascript
const { pipe } = require('@arrows/composition')
const result = pipe.now(
'arrows',
(text) => ${text}-suffix1,${text}-suffix2
(text) => ,`
) // -> "arrows-suffix1-suffix2"
---
Works like pipe, but additionally:
- if one of the functions throws or returns an error - returns that error,
- if one of the functions returns undefined - passes previous argument to the next function.
#### Parameters
Arguments listed below have to be passed separately, as segments.
- ...fns - an arbitrary number of one-argument functions to be executed in a chain
- initialArg - initial argument, passed to the first function in a chain
#### Returns
- Returns a final value.
#### Interface
`
(fn, fn?, ..., fn?) => (initial_value) => result
#### Examples
Automatically passing down an error:
`javascript
const { rail } = require('@arrows/composition')
const { filter, map, reduce } = require('@arrows/array')
const sumDogsAge = rail(
filter((pet) => pet.specie === 'dog'),
map((pet) => {
if (pet.age < 0) {
throw new Error('Wrong age!')
}
return pet.age
}),
reduce((a, b) => a + b, 0),
)
const pets = [
{ specie: 'dog', name: 'Charlie', age: 4 },
{ specie: 'cat', name: 'Luna', age: 6 },
{ specie: 'dog', name: 'Ollie', age: -10 },
]
const result = sumDogsAge(pets)
if (result instanceof Error) {
console.log('Oops!')
} else {
console.log(Sum: ${result})
}
// -> "Oops!"
`
Automatically passing previous argument, if function returns undefined:
`js
const { rail } = require('../../lib/index')
const addUser = rail(
(user) => ({ type: 'user', data: user }),
(entry) => {
console.log(Saving ${entry.data.name} to the database.)Saved user: ${entry.data.name}
// Returns undefined, argument will be automatically
// passed to the next function.
},
(entry) => ,
)
const user = { name: 'Joe' }
console.log(addUser(user))
/* Output:
Saving Joe to the database.
Saved user: Joe
*/
`
---
Works similar to rail, but additionally, if argument is a promise - resolves that promise before passing to the next function.
#### Parameters
Arguments listed below have to be passed separately, as segments.
- ...fns - an arbitrary number of one-argument functions to be executed in a chain
- initialArg - initial argument, passed to the first function in a chain
#### Returns
- Returns a final value wrapped in a promise.
#### Interface
`
(fn, fn?, ..., fn?) => (initial_value) => result
#### Example
Automatically passing down an error:
`javascript
const { railAsync } = require('../../lib/index')
const dbFake = {
id: 0,
save() {
const result = Promise.resolve(this.id)
this.id++
return result
},
}
const addArticle = railAsync(
(article) => ({ type: 'article', data: article }),
(entry) => dbFake.save(entry),
(id) => Article id: ${id},
)
const main = async () => {
const article = {
title: 'Railway oriented programming',
content: 'Lorem ipsum...',
}
const result = await addArticle(article)
console.log(result)
}
main() // -> "Article id: 0"
`
Works like rail, but executes functions from right to left.
Works like railAsync, but executes functions from right to left.
Executes provided function with provided argument and returns an argument without changes.
Useful for executing void functions without breaking the chain.
_Note: rail* functions handle this automatically, so you can use void functions directly._
#### Parameters
- fn - an arbitrary function
- arg - any value
#### Returns
- Returns argument as-is.
#### Interface
`
(fn, arg) => arg
Example:
`js
const { pipe, tap } = require('../../lib/index')
const { sort, reduce, _rest, _butLast } = require('@arrows/array')
const sumNotes = pipe(
sort((a, b) => a - b),
tap(console.log),
_rest,
tap(console.log),
_butLast,
tap(console.log),
reduce((a, b) => a + b, 0),
)
const notes = [16, 17.5, 19, 15, 18]
console.log(sumNotes(notes))
/* Output:
[ 15, 16, 17.5, 18, 19 ]
[ 16, 17.5, 18, 19 ]
[ 16, 17.5, 18 ]
51.5
*/
``
Project is under open, non-restrictive ISC license.