@arrows/composition
Table of contents
Introduction
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.
Installation
Via NPM:
npm i @arrows/composition
Via Yarn:
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):
import composition from '@arrows/composition'
import { pipe } from '@arrows/composition'
import pipe from '@arrows/composition/pipe'
API reference
chain
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
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)
chainRight
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
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)
compose
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
const { compose } = require('@arrows/composition')
const addPrefixes = compose(
(text) => `prefix1-${text}`,
(text) => `prefix2-${text}`,
)
addPrefixes('arrows') // -> "prefix1-prefix2-arrows"
curry
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
const { curry } = require('@arrows/composition')
const rawAdd = (a, b) => a + b
const add = curry(rawAdd)
add(1, 2) // -> 3
add(1)(2) // -> 3
pipe
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
const { pipe } = require('@arrows/composition')
const addSuffixes = pipe(
(text) => `${text}-suffix1`,
(text) => `${text}-suffix2`,
)
addSuffixes('arrows') // -> "arrows-suffix1-suffix2"
pipe.now
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
const { pipe } = require('@arrows/composition')
const result = pipe.now(
'arrows',
(text) => `${text}-suffix1`,
(text) => `${text}-suffix2`,
) // -> "arrows-suffix1-suffix2"
rail
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:
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:
const { rail } = require('../../lib/index')
const addUser = rail(
(user) => ({ type: 'user', data: user }),
(entry) => {
console.log(`Saving ${entry.data.name} to the database.`)
// Returns undefined, argument will be automatically
// passed to the next function.
},
(entry) => `Saved user: ${entry.data.name}`,
)
const user = { name: 'Joe' }
console.log(addUser(user))
/* Output:
Saving Joe to the database.
Saved user: Joe
*/
rail.async
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:
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"
railRight
Works like rail, but executes functions from right to left.
railRight.async
Works like railAsync, but executes functions from right to left.
tap
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:
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
*/
License
Project is under open, non-restrictive ISC license.