conductor/__tests__/compose.js

A modern & functional JavaScript utility library

const compose = require('../src/compose')
const delay = require('../src/delay')
const reduce = require('../src/reduce')

const add = (a, b) => a + b
const double = x => 2 * x
const add8 = x => x + 8
const minus4 = x => x - 4

const doubleAsync = x => Promise.resolve(double(x))
const add8Async = x => Promise.resolve(add8(x))
const minus4Async = x => Promise.resolve(minus4(x))
const toArray = (...args) => args // toArray.length === 0

describe('compose', () => {
  it('should compose synchronous functions (right-to-left)', () => {
    expect(
      compose(
        minus4,
        add8,
        double
      )(1)
    ).toBe(6)
  })

  it('should compose async functions', async () => {
    await expect(
      compose(
        minus4Async,
        delay(100),
        add8Async,
        doubleAsync
      )(1)
    ).resolves.toBe(6)
  })

  it('should compose both sync and async functions', async () => {
    await expect(
      compose(
        minus4,
        delay(100),
        add8,
        doubleAsync
      )(1)
    ).resolves.toBe(6)
  })

  it('should not break curryfication', () => {
    expect(
      compose(
        minus4,
        add
      )(2)(5)
    ).toBe(3)
    expect(
      compose(
        reduce(add, 0),
        toArray
      )(2, 3, 5)
    ).toBe(10)
  })
})