kefir/src/primary/from-events.js

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

import fromSubUnsub from './from-sub-unsub'

const pairs = [['addEventListener', 'removeEventListener'], ['addListener', 'removeListener'], ['on', 'off']]

export default function fromEvents(target, eventName, transformer) {
  let sub, unsub

  for (let i = 0; i < pairs.length; i++) {
    if (typeof target[pairs[i][0]] === 'function' && typeof target[pairs[i][1]] === 'function') {
      sub = pairs[i][0]
      unsub = pairs[i][1]
      break
    }
  }

  if (sub === undefined) {
    throw new Error(
      "target don't support any of " +
        'addEventListener/removeEventListener, addListener/removeListener, on/off method pair'
    )
  }

  return fromSubUnsub(
    handler => target[sub](eventName, handler),
    handler => target[unsub](eventName, handler),
    transformer
  ).setName('fromEvents')
}