context-fp

Microscopic functional programming context for TypeScript

Motivation

if you tired from gygantic TypeScript DI containers, based on classes and decorators, you are in the right place
Just use functional programming and don't worry about context passing through functions, it's with you

Features

• 🤏 Microscopic, few kilobytes size and most of it is TypeScript generics
• 💉 Dependency injection without classes and decorators, only functions
• 🤌 Functions cached during workflow, no excess cost of CPU
• 💡 Smart type inference, only describe type of context and rest will be inferred
• ♻️ Unit tests friendly, feel free to call any function directly in the workflow
• 📦 Tiny Redux like state manager also attached

How to

Basic example

import { cfp } from 'context-fp'
import assert from 'node:assert'

type Context = { numbers: number[] }

const positiveNumbers = ({ numbers }: Context) => numbers.filter(n => n > 0)

const numbersPrefix = () => 'Here is numbers:'

const positiveNumbersAsString = cfp(
  numbersPrefix,
  positiveNumbers,
  (prefix, numbers) => `${prefix} ${numbers.toString()}`
)

assert.strictEqual(
  positiveNumbersAsString({ numbers: [-1, -5, 7, 0, 4] }),
  'Here is numbers: 7,4'
)

Calculations cached example

import { cfp } from 'context-fp'
import assert from 'node:assert'

let called = 0

const positiveNumbers = ({ numbers }: { numbers: number[] }) =>
  (called++, numbers.filter(n => n > 0))

const positiveNumbersLength = cfp(positiveNumbers, ns => ns.length)

const positiveNumbersAsString = cfp(
  positiveNumbers,
  positiveNumbersLength,
  (ns, l) => `${ns.toString()}; length - ${l}`
)

assert.strictEqual(
  positiveNumbersAsString({ numbers: [-1, -5, 7, 0, 4] }),
  '7,4; length - 2'
)
assert.strictEqual(called, 1)

Unit tests example

import { cfp } from 'context-fp'
import assert from 'node:assert'

type Context = { numbers: number[] }

const positiveNumbers = ({ numbers }: Context) => numbers.filter(n => n > 0)

const numbersPrefix = () => 'Here is numbers:'

const positiveNumbersAsString = cfp(
  numbersPrefix,
  positiveNumbers,
  (prefix, numbers) => `${prefix} ${numbers.toString()}`
)

assert.strictEqual(
  positiveNumbersAsString.raw('Here is numbers:', [7, 4]),
  'Here is numbers: 7,4'
)

Dependency injection example

import { cfp } from 'context-fp'
import assert from 'node:assert'

const fetchUserFromDB = async (): Promise<{ name: string }> => {
  // some production implementation
}

const fetchUser = ({ fetchUser }: { fetchUser?: typeof fetchUserFromDB }) =>
  fetchUser?.() ?? fetchUserFromDB()

const helloWorldUser = cfp(
  fetchUser,
  user => user.then(({ name }) => `Hello world, ${name}!`)
)

assert.strictEqual(
  await helloWorldUser({ fetchUser: async () => ({ name: 'Vasya' }) }),
  'Hello world, Vasya!'
)

State manager example

import { cfp, sfp } from 'context-fp'
import assert from 'node:assert'

const numbers = ({ incNumber }: { incNumber: number }) =>
  sfp((ns: number[], n: number) => [...ns, n + incNumber], [])

const addNumber1 = cfp(numbers, ns => ns(1))
const addNumber2 = cfp(numbers, ns => ns(2))
const addNumber3 = cfp(numbers, ns => ns(3))

const numbersToString = cfp(
  numbers,
  addNumber1,
  addNumber2,
  addNumber3,
  ns => ns().toString()
)

assert.strictEqual(numbersToString({ incNumber: 1 }), '2,3,4')

See also

• context-fp-go - Functional programming context for Golang
• functx - Functional programming context for Gleam