kefir/src/interop/to-promise.js

Reactive Programming library for JavaScript inspired by Bacon.js and RxJS with focus on high performance and low memory usage

import {VALUE, END} from '../constants'

function getGlodalPromise() {
  if (typeof Promise === 'function') {
    return Promise
  } else {
    throw new Error("There isn't default Promise, use shim or parameter")
  }
}

export default function(obs, Promise = getGlodalPromise()) {
  let last = null
  return new Promise((resolve, reject) => {
    obs.onAny(event => {
      if (event.type === END && last !== null) {
        ;(last.type === VALUE ? resolve : reject)(last.value)
        last = null
      } else {
        last = event
      }
    })
  })
}