kefir/src/interop/to-es-observable.js

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

import {extend} from '../utils/objects'
import {VALUE, ERROR, END} from '../constants'
import $$observable from './symbol'

function ESObservable(observable) {
  this._observable = observable.takeErrors(1)
}

extend(ESObservable.prototype, {
  subscribe(observerOrOnNext, onError, onComplete) {
    const observer =
      typeof observerOrOnNext === 'function'
        ? {next: observerOrOnNext, error: onError, complete: onComplete}
        : observerOrOnNext

    const fn = event => {
      if (event.type === END) {
        closed = true
      }

      if (event.type === VALUE && observer.next) {
        observer.next(event.value)
      } else if (event.type === ERROR && observer.error) {
        observer.error(event.value)
      } else if (event.type === END && observer.complete) {
        observer.complete(event.value)
      }
    }

    this._observable.onAny(fn)
    let closed = false

    const subscription = {
      unsubscribe: () => {
        closed = true
        this._observable.offAny(fn)
      },
      get closed() {
        return closed
      },
    }
    return subscription
  },
})

// Need to assign directly b/c Symbols aren't enumerable.
ESObservable.prototype[$$observable] = function() {
  return this
}

export default function toESObservable() {
  return new ESObservable(this)
}