[Wirte once algorithm for sync & async function]

example.js

import co from 'co' // or whatever like co
import fetch from './fetch_data_synchronously'
import fetchAsync from './fetch_data_asynchronously'

export function process() {
  const generator = processAlgorithmGenerator(fetch)
  let next = { done: false }
  while(!next.done) {
    next = generator.next(next.value)
  }
  return next.value
}

export function processAsync() {
  return co(processAlgorithmGenerator)(fetchAsync)
}

function* processAlgorithmGenerator(fetch) {
  const nes = []
  let index = 0
  while (true) {
    let ne = yield fetch(index)
    if (!ne) break
    nes.push(ne)
    index += 1
  }
  return nes
}