Implement bluebird's Promise.map & Promise.filter with native Promise

Promise.js

Promise.map = function (iterable, mapper, options) {
  options = options || {}
  let concurrency = options.concurrency || Infinity

  let index = 0
  const results = []
  const iterator = iterable[Symbol.iterator]()
  const promises = []

  while (concurrency-- > 0) {
    const promise = wrappedMapper()
    if (promise) promises.push(promise)
    else break
  }

  return Promise.all(promises).then(() => results)

  function wrappedMapper () {
    const next = iterator.next()
    if (next.done) return null
    const i = index++
    const mapped = mapper(next.value, i)
    return Promise.resolve(mapped).then(resolved => {
      results[i] = resolved
      return wrappedMapper()
    })
  }
}

Promise.filter = function (iterable, filterer, options) {
  options = options || {}
  let concurrency = options.concurrency || Infinity

  let index = 0
  const results = []
  const predicates = []
  const iterator = iterable[Symbol.iterator]()
  const promises = []

  while (concurrency-- > 0) {
    const promise = wrappedFilterer()
    if (promise) promises.push(promise)
    else break
  }

  return Promise.all(promises).then(() => results.filter((v, i) => predicates[i]))

  function wrappedFilterer () {
    const next = iterator.next()
    if (next.done) return null
    const i = index++
    results.push(next.value)
    const predicate = filterer(next.value, i)
    return Promise.resolve(predicate).then(resolved => {
      predicates[i] = resolved
      return wrappedFilterer()
    })
  }
}