Declarative asynchonous control flow: promises, observables, futures

solution1.js

const wrapPromise = fn => (...args) =>
  new Promise(resolve => setTimeout(
    () => resolve(fn(...args)),
    Math.floor(Math.random() * 1500) + 250)
  )
const upper = wrapPromise(str => str.toUpperCase())
const underline = str => `__${str}__`
const exclamate = wrapPromise(str => str + '!')

// Util: Create promise chain
const chainPromises = (...fns) => val =>
  fns.reduce((ch, fn) => ch.then(fn), Promise.resolve(val))

// Create function chain with mixed sync and async functions
const chain1 = chainPromises(upper, underline, exclamate, console.log)

;['aap', 'noot', 'mies'].forEach(chain1)

solution2.js

const Observable = require('zen-observable')

const wrapPromise = fn => (...args) =>
  new Promise(resolve => setTimeout(
    () => resolve(fn(...args)),
    Math.floor(Math.random() * 1500) + 250)
  )
const upper = wrapPromise(str => str.toUpperCase())
const underline = str => `__${str}__`
const exclamate = wrapPromise(str => str + '!')

// Util: Promise to Observable
const wrapObservable = fn => (...args) =>
  new Observable(observer => {
    fn(...args).then(val => observer.next(val))
  })

// Create function chain with mixed sync and async functions
const chain2 = Observable.from(['wim', 'zus', 'jet'])
  .flatMap(wrapObservable(upper))
  .map(underline)
  .flatMap(wrapObservable(exclamate))

chain2.subscribe(console.log)

solution3.js

const { map, chain, pipe } = require('ramda')
const { Future, fork } = require('fluture')

const wrapFuture = fn => (...args) =>
  Future((_reject, resolve) => {
    setTimeout(
      () => resolve(fn(...args)),
      Math.floor(Math.random() * 1500) + 250
    )
  })
const upper = wrapFuture(str => str.toUpperCase())
const underline = str => `__${str}__`
const exclamate = wrapFuture(str => str + '!')

// Create function chain with mixed sync and async functions
const chain3 = pipe(
  Future.resolve,
  chain(upper),
  map(underline),
  chain(exclamate),
  fork(console.error)(console.log)
)

map(chain3)(['teun', 'vuur', 'gijs'])